Labs

Rapid Review

• Background
  • The typical basic serum toxin panel checks for the presence of several common toxins, including ethyl alcohol (ethanol), salicylates (aspirin) and acetaminophen (Tylenol)
• When to Order
  • Suspected acetaminophen overdose or any suicide attempt potentially involving PO ingestion. 
• Interpretation
  • Normal Range (Adults and Children)
    • 10-30 mcg/mL
  • Toxic ingestion 4 hours after ingestion
    • > 140 – 150 mcg/mL
  • Toxic ingestion 12 hours after ingestion
    • > 50 mcg/mL

Pearls

• Acetaminophen levels typically peak between 30 minutes and 2 hours, but may be delayed in neonates due to prolonged gastric emptying.
• When applied to the Rumack-Matthew nomagram, acetaminophen levels obtained 4-15 hours after a single ingestion are the most predictive of hepatoxicity.

Deep Dive

• Acetaminophen Level (EBM Consult)

Rapid Review

• Background
  • Albumin is the most abundant protein in plasma, playing a pivotal role in controlling oncotic pressure. It is mainly synthesized in the liver and is considered to be a true measurement of hepatic function.
• When to Order
  • Suspected liver disease
  • Suspected kidney disease
• Interpretation
  • Normal Range
    • 3.5-5.5 g/dL
  • Hyperalbuminemia
    • Dehydration, high-protein diet
  • Hypoalbuminemia
    • Liver disease, ascites, burns, malnutrition, malabsorption syndromes

Deep Dive

• Severity of SARS-COV-2 infection and albumin levels recorded at the first emergency department evaluation (PubMed)

Rapid Review

• Background
  • Alkaline phosphatase is an enzyme responsible for transferring metabolites across cell membranes. It is mostly used to detect liver injury, though it is considered more specific to the biliary tract. ALP can be elevated via several processes throughout the body (bone, intestines, kidney, placenta), so it is recommended to also order Gamma-glutamyl transpeptidase to narrow the differential.
• When to Order
  • Suspected hepatic injury
  • Suspected biliary disease
• Interpretation
  • Elevated ALP + Elevated GGT
    • Hepatic origin
      • Hepatitis, biliary cirrhosis, choledocholithiasis
  • Elevated ALP + Normal GGT
    • Non-hepatic origin
      • Metastatic disease, healing fracture, osteomalacia, renal failure, heart failure, hyperparathyroid

Pearls

• Alkaline phosphatase levels will typically be elevated before the rise in bilirubin during biliary obstruction. 
• Approximately 30-40% of patients with cholecystitis will have an elevated alkaline phosphatase. 

Deep Dive

• Liver Function Tests Decoded (Taming the SRU)

Rapid Review

• Background
  • Amylase is a digestive enzyme produced in the pancreas and salivary glands. In addition to lipase, It is commonly used as a marker of acute pancreatitis. Elevated amylase can also be seen in biliary obstruction, trauma, or diseases in the salivary glands or intestinal tract. It can also be due to non-pancreatic causes such as diseases of the salivary glands or intestinal tract.
• When to Order
  • Abdominal pain, suspicion for acute pancreatitis
• Interpretation
  • Normal Range
    • 60 – 120 Somogyi units/dL or 30 – 220 units/L (SI units)
  • Acute pancreatitis
    • Level > 4 times ULN within 48 hours is highly suggestive of diagnosis

Pearls

• Amylase has largely been replaced by lipase for the evaluation of pancreatitis due to better specificity. 
• Amylase levels typically peak within 24-36 hours of initial insult of disease, and fall within 48 hours.

Deep Dive

• Eliminating Amylase Testing from the Evaluation of Pancreatitis in the Emergency Department (PubMed)

Rapid Review

• Background
  • An arterial blood gas (ABG) measures the acidity of the blood as well as the presence of oxygen and carbon dioxide. It can be used to evaluate the acid-base status of the body, check for hypercapnia (high CO2), and evaluate for hypoxia (low oxygen levels).
• Findings/Interpretation
  • Respiratory Acidosis
    • pH ↓  CO2 ↑  Bicarb (normal)
    • Causes include hypoventilation, COPD, asthma
  • Respiratory Alkalosis
    • pH ↑ CO2 ↓  Bicarb (normal)
    • Causes include hyperventilation, altitude sickness, hepatic failure, anxiety
  • Metabolic Acidosis
    • pH ↓  CO2 (normal)  Bicarb ↓
    • Causes include DKA, sepsis, severe diarrhea
  • Metabolic Alkalosis
    • pH ↑ CO2 (normal)  Bicarb ↑
    • Causes include severe vomiting, Cushing’s disease, nasogastric tube suction, diuretics

Pearls

• If there is concern for first stick accuracy, ultrasound can help identify the best site.
• Arterial blood gas measurements should still be used for critically ill acidotic patients, but for routine DKA or COPD patients, a venous blood gas is acceptable. 

Deep Dive

• VBG vs ABG in the ED (NUEM)

Rapid Review

• Background
  • Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are hepatic enzymes that are released in response to hepatocellular injury. AST is additionally expressed in the brain, skeletal muscle, heart, and kidney, whereas ALT is considered to be more specific to liver damage.
• When to Order
  • Suspected liver disease (jaundice, pale stool, AMS, abdominal pain)
  • Suspected acetaminophen overdose 
• Interpretation
  • Mild Transaminase Elevation (< 5X upper limit of normal)
    • Drug-induced liver injury (aspirin, statins, barbiturates, herbs, HIV medication)
    • Alcohol-induced injury
    • Non-alcoholic fatty liver disease
    • Mononucleosis
  • Moderate Transaminase Elevation (5-10X upper limit of normal)
    • Alcoholic hepatitis
    • Biliary tract disease (gallstones, biliary infection, cholangitis)
  • Severe Transaminase Elevation (>10X upper limit of normal)
    • Viral Hepatitis
    • Acetaminophen toxicity
    • Ischemic hepatitis (“shock liver”)

Pearls

• Vitamin B6 depletion can artificially lower ALT and AST levels. 
• Liver diseases that cause higher levels of AST compared to ALT include liver tumors, cirrhosis, and alcohol induced liver damage. 

Deep Dive

• Elevated Liver Enzymes: ED-focused Management Pearls & Pitfalls (emDocs)

Rapid Review

• Background
  • The basic chemistry panel – also called BMP or Chem 7 – evaluates several key electrolytes in the blood as well as marker of renal function. This includes sodium (Na), potassium (K), chloride (Cl), carbon dioxide (CO2), blood urea nitrogen (BUN), creatinine and glucose
• Findings/Interpretation
  • Hypernatremia
    • Dehydration, diabetes insipidus, Cushing’s disease
  • Hyponatremia
    • Excess body water (CHF, renal failure, etc.), hypothyroidism, vomiting, diarrhea, pancreatitis
  • Hyperkalemia
    • Renal failure, Addison’s disease, dehydration, ACE inhibitors, spironolactone
  • Hypokalemia
    • Diuretics, NG suctioning, vomiting, diarrhea, metabolic alkalosis
  • Hypercalcemia
    • Hyperparathyroidism, malignancy, renal failure, thiazides, Addison’s disease, vitamin D intoxication
  • Hypocalcemia
    • Hypoparathyroidism, vitamin D deficiency, alcoholism, sepsis, pancreatitis, hypomagnesemia
  • Hyperchloremia
    • Diarrhea, hyperalimentation
  • Hypochloremia
    • Vomiting, renal disease, diabetic ketoacidosis
  • Hyperglycemia
    • Diabetes, Cushing’s syndrome, pancreatitis, thiazide diuretics
  • Hypoglycemia
    • Liver disease, malnutrition, sepsis, endocrine tumors
  • Azotemia
    • Renal injury/failure, CHF, aminoglycosides

Pearls

• Hyperglycemia can cause a falsely lowered sodium level. Every 100 mg/dL of glucose above the normal range decreases sodium by approximately 1.6 mmol/L
• Significantly levated potassium levels (without symptoms or EKG changes) may be erroneous values caused by hemolysis of the sample or prolonged tourniquet use during venipuncture.

Deep Dive

• Use of a Comprehensive Metabolic Panel Point-of-Care Test to Reduce Length of Stay in the Emergency Department: A Randomized Controlled Trial (Annals of Emergency Medicine)

Rapid Review

• Background
  • Bilirubin is a breakdown product of hemoglobin degradation. Unconjugated (indirect) bilirubin refers to bilirubin that is bound to albumin inside the vascular space. In the liver, it is then converted to its excretable, water-soluble format as conjugated (direct) bilirubin.
• When to Order
  • Suspected biliary disease
  • Suspected liver disease
• Interpretation
  • Normal Range
    • Total bilirubin: 0.3-1.0 mg/dL
    • Indirect bilirubin: 0.2-0.8 mg/dL
    • Direct bilirubin: 0.1-0.3 mg/dL
  • Unconjugated Hyperbilirubinemia
    • Indicates increased hemolysis. Common in newborns and sickle cell patients.
  • Conjugated Hyperbilirubinemia
    • Biliary obstruction, hepatocellular injuries, infections, drugs, sepsis

Pearls

• Jaundice typically becomes apparent once total bilirubin levels reach 2-3 mg/dL
• The total bilirubin level is not a sensitive marker for hepatic dysfunction. Total bilirubin can remain normal despite even the worst hepatic diseases.

Deep Dive

• Bilirubin Level (EBM-Consult)

Rapid Review

• Background
  • A blood culture is used to detect the presence and type of bacteria in the blood for the purpose of guiding antimicrobial therapy. The culture is grown in the lab for days until the bacteria can be identified. These can also be used to test for susceptibility to different antibiotics. Results are not available right away.
• When to Order
  • Patients who meet SIRS criteria
  • Unstable patients with suspected bacterial infections 
  • Concern for indwelling catheter/line infection
  • Febrile neutropenia or immunocompromised patients
• Interpretation
  • Negative growth
    • Normal in healthy patients, but cannot definitively rule out infection
  • Positive growth
    • Most common pathogens in the ED include E. coli, Klebsiella spp, Staphylococcus spp, Streptococcus spp, and Pseudomonas spp. (together make up 80% of all culture specimens)
    • Common contaminants include Staphylococcus epidermidis, Bacillus spp, Propionibacterium acnes, Corynebacterium spp, Streptococcus (Viridans), and Clostridium perfringens.

Pearls

• Blood cultures should be collected using aseptic technique and prior to beginning antibiotic therapy.
• False-positive blood cultures are common and are associated with 3-5 day increases in hospital length of stay and $4,000 to $9,000 in additional costs. Be selective in who you choose to get blood cultures on.

Deep Dive

• “So, Blood Cultures… or No?” – Use of Blood Cultures in the ED (emDocs)

Rapid Review

• Background
  • A blood type and screening test is a rapid lab test used to identify blood compatibility in case of the need for transfusion. The “Type” part identifies both the blood type (A,B,AB or O) and rhesus factor (+ or -). The “Screen” portion screens for common antibodies that may complicate blood transfusion (Rh, Kell, Duffy, etc.).
• When to Order
  • Any chance that a patient may require a blood transfusion
• Interpretation
  • O-
    • Can only receive O- blood
  • O+
    • Can receive O- or O+
  • A-
    • Can receive O- or A-
  • A+
    • Can receive O-, O+, A-, or A+
  • B-
    • Can receive O- or B-
  • B+
    • Can receive O-, O+, B-, B+
  • AB-
    • Can receive O-, A-, B-, or AB-
  • AB+
    • Can receive all blood types
  • Presence of minor antibody groups (Rh, Kell, Duffy)
    • May complicate transfusion. Requires a crossmatch with the donor blood.

Pearls

• Certain malignancies and bacterial infections may cause an A-type individual to be falsely categorized as B-type.
• A type and screen will test for ABO, Rh, and antibodies, but will NOT cross-match with donor blood to ensure compatibility. This requires a specific “Type and Cross” order. 

Deep Dive

• When to Group & Screen and Cross Match (Emergency Medicine Cases)

Rapid Review

• Background
  • Crossmatch involves combining the patient’s blood and the donor’s blood to observe for any adverse reaction (ex. clumping).  Blood from the blood bank that matches both the patient’s  major and minor antibody groups are then reserved for transfusion to the patient.
• When to Order
  • Any patient needing a blood transfusion that comes up positive for any minor antibody groups (Rh, Kelly, Duffy, etc.) on the type and screen test
• Interpretation
  • N/A

Pearls

• Type and cross should not be routinely obtained for every patient who may need a transfusion. Reserve this test for those who test positive for any of the minor antibody groups. 
• In a patient who needs an emergent blood transfusion, do NOT wait for the results of the cross match.

Deep Dive

• When to Group & Screen and Cross Match (Emergency Medicine Cases)

Rapid Review

• Background
  • Brain natriuretic peptide is a hormone released from cardiac cells that can be used to evaluate and manage ventricular dysfunction and fluid overload.
• When to Order
  • Suspected heart failure
  • Suspected pulmonary embolism
• Interpretation
  • BNP < 50 pg/mL
    • Indicates absence of CHF
  • BNP  100-400 pg/mL
    • May suggest CHF. May also be increased due to increased age, decreased BMI, cardiomegaly, atrial fibrillation, or low hemoglobin
  • BNP > 400 pg/mL
    • Strongly suggestive of CHF

Pearls

• Obesity can be cause falsely low levels of natriuretic peptides despite clinical findings of heart failure.
• BNPh has prognostic value for several conditions, including CAD, valvular disease, CKD, and CHF. In all cases, a higher BNP portends a poor prognosis.

Deep Dive

• BNP in the Emergency Department (First 10 EM)

Rapid Review

• Background
  • Ionized calcium measures the amount of free calcium in the blood. This is the most active form compared to calcium ions bound to other proteins. Ionized calcium is more accurate than a serum calcium level because it is unaffected by changes in serum albumin levels
• When to Order
  • Any critically ill patient
  • Signs of hypercalcemia or hyperparathyroidism
    • “Stones (renal), Bones (bone pain), Groans (abdominal pain), Moans (psychiatric overtones)
    • Bradydysrhythmias, AMS
  • Signs of hypocalcemia or hypoparathyroidism
    • Paresthesia, muscle spasms, Chovostek’s sign, Trousseau’s sign
    • AMS, QT prolongation, hypotension
• Interpretation
  • Hypercalcemia (> 7 mg/dL)
    • Causes include hyperparathyroidism, adrenal insufficiency, dehydration, rhabdomyolysis, prolonged immobilization, malignancy, thiazide diuretics
  • Hypocalcemia (< 2.0 mg/dL)
    • Causes include hypoparathyroidism, chronic renal failure, hypomagnesemia, hyperphosphatemia, severe pancreatitis, calcitonin, bisphosphonates, massive blood transfusion

Pearls

• Prolonged tourniquet time during venipuncture can falsey elevated calcium levels.
• A hight total calcium, but normal ionized calcium, is referred to as pseudohypercalcemia. This can be caused by hyperalbuminemia, multiple myeloma, or increased exogenous vitamin D intake.

Deep Dive

• Calcium Ionized (MedScape)

Rapid Review

• Background
  • The calcium test measures the total amount of calcium in the blood. Abnormal calcium levels can be due to problems with the parathyroid gland, kidney disease or certain cancers.
• When to Order
  • Any critically ill patient
  • Signs of hypercalcemia or hyperparathyroidism
    • “Stones (renal), Bones (bone pain), Groans (abdominal pain), Moans (psychiatric overtones)
    • Bradydysrhythmias, AMS
  • Signs of hypocalcemia or hypoparathyroidism
    • Paresthesia, muscle spasms, Chovostek’s sign, Trousseau’s sign
    • AMS, QT prolongation, hypotension
• Interpretation
  • Hypercalcemia (> 10.5 mg/dL)
    • Causes include hyperparathyroidism, adrenal insufficiency, dehydration, rhabdomyolysis, prolonged immobilization, malignancy, thiazide diuretics
  • Hypocalcemia (< 8.5 m mg/dL)
    • Causes include hypoparathyroidism, chronic renal failure, hypomagnesemia, hyperphosphatemia, severe pancreatitis, calcitonin, bisphosphonates, massive blood transfusion

Pearls

• Approximately 40% of serum calcium is bound to proteins, particularly albumin. This can greatly misrepresent results if albumin levels are distorted. For true measurement of free calcium circulating in the blood, you will need to order an “ionized calcium” level.
• A clenched fist, forearm exercise, or prolonged tourniquet time during venipuncture can falsey elevate calcium levels.

Deep Dive

• Serum Calcium (MedScape)

Rapid Review

• Background
  • The coagulation panel consists of two different measures of blood clotting. Prothrombin time (PT) and partial thromboplastin time (PTT) can be increased due to underlying conditions or blood thinning medications
• Findings/Interpretation
  • Prolonged PT (INR)
    • Warfarin (low dose)
    • Mild vitamin K deficiency
    • Factor VII deficiency
  • Prolonged APTT
    • Von Willebrand disease
    • Unfractionated heparin
    • Overcoagulation w/ low molecular weight heparin
    • Factor inhibitors
    • Factor VIII, IX, VI, or XII deficiency
    • Antiphosopholipid antibody
  • Prolonged PT(INR) and APTT
    • Liver disease
    • DIC
    • High hematocrit
    • Common pathway deficiency (X, V, II, fibrinogen)
    • Excess heparin
    • Severe vitamin K deficiency
    • Factor IIa inhibitors (dabigatran
    • Factor Xa inhibitors (rivaroxaban, apixaban)

Pearls

• Although coagulation panels are routinely sent for pre-operative screening,they rarely change management and an abnormal test does not accurately predict bleeding risk. 
• Ordering both a PT/INR and PTT is rarely needed. Only order both if there is active bleeding or a suspected coagulopathy (e.g. DIC)

Deep Dive

• When should you obtain coagulation tests in the emergency department? (emDocs)

Rapid Review

• Background
  • The complete blood count (CBC) measures multiple types of blood cells. This includes the number of white blood cells, considered a marker of infection or inflammation; amount and percentage of red blood cells, the oxygen carrying cells; and platelets which are a key component of blood clotting
• Findings/Interpretation
  • WBC
    • Leukocytosis
      • Infection, pain, surgery, hypoxia, trauma, burns, infarctions, uremia, DKA, drugs (epinephrine, corticosteroids, lithium, cocaine)
    • Leukopenia
      • Malignancy, B12 or folate deficiency, aplastic anemia, sepsis, autoimmune disorders, splenic sequestration, radiation exposure
  • Hemoglobin
    • Anemia
      • Hemorrhage, iron deficiency, chronic disease, cancer, HIV, nutritional deficiencies (iron, B12, folate, malnutrition), hemolytic disease, pregnancy.
    • Polycythemia
      • Dehydration, tobacco use, renal cell carcinoma, chronic heart/lung disease, living at high altitude, hydronephrosis, EPO-secreting tumor, myeloproliferative disease
  • MCV
    • Microcytosis
      • “TICS” (Thalassemia, iron-deficiency, chronic disease, sideroblastic anemia)
    • Macrocytosis
      • B12 deficiency, folate deficiency, alcohol, liver disease, hypothyroidism
  • Platelets
    • Thrombocytopenia
      • Splenic sequestration, DIC, heparin-induced, nutritional deficiency (B12 or folate), liver disease, metastatic tumors, aplastic anemia, myelodysplasia
    • Thrombocytosis
      • Infection/sepsis, solid organ malignancies, post-splenectomy, anemia, chronic inflammatory disorders (TB, sarcoidosis, auto-immune), polycythemia vera, myelofibrosis, chronic myeloid leukemia

Pearls

• A CBC w/ differential has the advantage of identifying the count of each type of white blood cell (ex. neutrophils, lymphocytes, monocytes, eosinophils, and basophils)
• A WBC with “left shift” refers to the increase of bands (immature neutrophils). This is representative of an infection in progress.

Deep Dive

• The CBC and the Man Behind the Curtain (Taming the SRU)

Rapid Review

• Background
  • Creatine kinase, also called creatine phosphokinase, is an enzyme found in muscle throughout the body. Elevated levels can be seen in conditions of muscle breakdown, such as rhabdomyolysis, myopathies, drug side effects or excessive exercise.
• When to Order
  • Assessment of muscle pain, weakness, or dark urine
  • Mechanisms suspicious for rhabdomyolysis (strenuous exercise, crush injury, seizure, lighting strike, immobilization, heat stroke, infection, illicit drug use)
• Interpretation
  • Normal
    • Male (55-170 units/L)
    • Female (30-135 units/L)
  • Elevated Creatinine Kinase
    • May indicated rhabdomyolysis, malignant hyperthermia, muscular dystrophy, drug-induced myopathy
    • Recent strenuous exercise will naturally elevate levels

Pearls

• Creatinine kinase levels rise within about 6 hours after muscle damage, peak at about 18 hours, and return to normal in 2-3 days.
• Intramuscular injections alone can cause elevated CK levels.

Deep Dive

• The Utility of Serum Creatinine Kinase in the Emergency Department (PubMed)

Rapid Review

• Background
  • Cerebrospinal fluid (CSF) is produced in the choroid plexuses of the ventricles in the brain and is found throughout the entire central nervous system (brain and spinal cord). CSF analysis involves the measurement of opening pressure, color, protein, glucose, gram stain, WBC, and RBCs
• When to Order
  • Suspected CNS infection (viral or bacterial)
  • Suspected subarachnoid hemorrhage
• Interpretation
  • Normal Findings
    • Opening Pressure: 5-20 cmH20
    • Appearance: clear, colorless
    • WBC: < 5
    • RBC: < 10
    • Protein: < 40 mg/dL
    • Glucose: > 60% serum glucose
  • Viral Infection
    • Opening Pressure: normal/elevated
    • Appearance: clear
    • WBC: elevated (10-2000)
    • RBC: normal
    • Protein: elevated
    • Glucose: >50%
  • Bacterial Infection
    • Opening Pressure: normal/elevated
    • Appearance: turbid, purulent
    • WBC: elevated (1000-5000)
    • RBC: normal
    • Protein: elevated
    • Glucose: decreased (< 50%)
  • Subarachnoid Hemorrhage
    • Opening Pressure: elevated
    • Appearance: blood stained/xanthochromic
    • WBC: normal/elevated
    • RBC: elevated
    • Protein: elevated
    • Glucose: normal

Pearls

• A “traumatic tap” (contamination of blood in the CSF sample) can muddy up the WBC count. However, you can correct this by using a calculation on MDCalc. In general, you are allowed 1 WBC for every 500 RBCs assuming the WBC count in the blood is normal. 
• CSF needs to be analyzed within 1 hour of collection. If delayed, cell counts may be falsey decreased due to adherence to the tubes.

Deep Dive

• What’s in a Tap: CSF Analysis (Taming the SRU)

Rapid Review

• Background
  • D-dimer is a product of fibrin degradation that becomes elevated during the lysis of clots. It reflects ongoing activation of the hemostatic system and is commonly used to evaluate for thrombotic conditions.
• When to Order
  • Suspected pulmonary embolism
  • Suspected deep vein thrombosis
• Interpretation
  • Normal (< 0.5 mcg/mL)
    • May sufficiently rule out pulmonary embolism or DVT if low pretest probability
  • Elevated D-Dimer (> 0.5 mcg/mL)
    • Requires further imaging to definitely diagnosis PE/DVT
    • May also be elevated in cancer, infection, trauma, pregnancy, thrombolytic therapy, burns, stroke, or liver disease

Pearls

• Generally speaking, D-dimer has a high sensitivity but low specificity. Do not order it unless you are prepared to take the next step after a positive result (e.g. CT angiogram or DVT Ultrasound)
• In patients with a high pretest probability of having pulmonary embolism or DVT, a D-dimer is useless. Just order the imaging!

Deep Dive

• D-Dimer How To (NUEM)

Rapid Review

• Background
  • Quantitative measurement of ethanol in the blood for the assessment of suspected recent alcohol ingestion. 
• When to Order
  • Suspected alcohol toxicity
  • Psychiatric emergency or history of coingestants
  • Presentation of coma or altered mental status
• Interpretation
  • Blood ethanol < 50
    • Not considered intoxicated
  • Blood ethanol 100 – 300
    • Acute intoxication
    • Gross motor impairment, dysphoria, blurred vision, confusion, loss of consciousness
  • Blood ethanol > 400
    • Considered lethal dose
    • Coma, respiratory depression/arrest

Pearls

• Do not allow an elevated ethanol level in a patient with AMS to keep you from considering other life-threatening differentials.
• The ethanol level may not always correlate with the clinical presentation of a patient with underlying alcoholism. These patients can often function at normal capacity with remarkably high levels.

Deep Dive

• Ethanol Level (MedScape)

Rapid Review

• Background
  • Lactate or lactic acid is used as a measure of tissue oxygenation and perfusion. Lactate is a normal product of cellular metabolism. Elevated lactate levels (type A) can be seen in conditions of hypoperfusion such as sepsis, hypovolemia, cardiac failure, seizure or cardiac arrest. Type B occurs without hypoperfusion and can be seen in diabetes, alcoholism and other conditions.
• Findings/Interpretation
  • Lactic Acidosis
    • Type A (tissue hypoperfusion)
      • Hypovolemia
      • Sepsis
      • Cardiac failure
    • Type B (decreased utilization)
      • DKA
      • Metformin
      • Alcoholism
      • Liver disease

Pearls

• An elevated lactate doesn’t always correlate with dangerous conditions. If the patient appears clinically well and hemodynamically stable, it’s reasonable to to give fluids and recheck a lactate level in 2 hours.
• A negative lactate doesn’t reliably rule out critical conditions. Correlate clinically.

Deep Dive

• Utility of Obtaining a Lactate Measurement in the ED (emDocs)

Rapid Review

• Background
  • Lipase is used as a marker of pancreatic damage or dysfunction. Elevated lipase as well as amylase is seen in pancreatitis, biliary obstruction or trauma. It can also be due to non-pancreatic causes such as diseases of the salivary glands or intestinal tract.
• When to Order
  • Suspected acute pancreatitis
• Interpretation
  • Normal Range
    • 0-160 units/L
  • Acute Pancreatitis
    • 2-3 times the upper limit of normal for patient
    • Lipase levels increase within 4-8 hours after onset, peaks at 24 hours, and decreases within 8-14 days

Pearls

• Lipase levels increase within 4-8 hours and peak at 24 hours. If lipase levels continue to increase beyond 14 days, this can indicate a poor prognosis or the presence of a pancreatic cyst.
• Lipase levels have largely replaced amylase levels for the evaluation of acute pancreatitis due to better sensitivity and specificity.

Deep Dive

• Lipase Level (Medscape)

Rapid Review

• Background
  • Magnesium is an intracellular cation needed for neuromuscular. It is also a cofactor for over 300 different enzymes, including those necessary for glucose control, energy production, and regulation of blood pressure/cardiac rhythm
• When to Order
  • Cardiac dysrhythmias
  • Suspected malnutrition/malabsorption
  • Neuromuscular signs/symptoms
• Interpretation
  • Normal Range
    • 1.3-2.1 mEq/L 
  • Hypomagnesemia (< 0.5 mEq/L)
    • Consider DKA, malabsorption, alcoholism, or hyperparathyroidism
  • Hypermagnesemia (> 3 mEq/L)
    • Consider Addison disease, renal insufficiency, hypothyroidism, or ingestion of magnesium-containing antacids

Pearls

• Approximately 99% of total body magnesium is locked up in muscles and bone. Because only 1% of magnesium is found in extracellular fluid, serum magnesium levels may not accurately reflect total body magnesium.
• Hypomagnesemia is often associated with other electrolyte abnormalities, such as hypocalcemia and hypokalemia.

Deep Dive

• The Significance of Routine Serum Magnesium Determination in the ED (Science Direct)

Rapid Review

• Background
  • The serum osmolality is a measure of the concentrations of solutes in the blood plasma. An elevated osmolality suggests the presence of other solutes, such as ethanol, toxic alcohols (methanol, ethylene glycol), ketoacidosis or lactic acidosis
• When to Order
  • To evaluate the etiology of hyponatremia
  • Screening for alcohol intoxication (via calculation of osmolar gap)
• Interpretation
  • Hypotonic (< 280 mOsm/kg)
    • Several potential causes, such as vomiting/diarrhea, SIADH, renal failure, adrenal insufficiency, diuretics.
    • Further testing (Urine Na and Urine Osmolality) required to narrow differential
  • Isotonic (280-295 mOsm/kg)
    • Consider hyperproteinemia or hyperlipidemia as causes.
  • Hypertonic (> 295 mOsm/kg)
    • Consider hyperglycemia, recent mannitol administration, or radiocontrast agents as causes.

Pearls

• To confirm the presence of an unmeasured solute in the blood (ex. toxic alcohol, sorbitol, mannitol), you can calculate an “Osmolar gap” (serum osmolality – calculated osmolarity).  Calculated osmolarity = (2 x [Na+]) + [glucose] + [urea])
• A serum osmolality level should always be interpreted in conjunction with a careful history and physical exam.

Deep Dive

• Serum Osmolality (Medscape)

Rapid Review

• Background
  • A peripheral smear is a blood slide that is manually reviewed by a pathologist to detect abnormal blood cells. It can detect a wide range of abnormal red blood cell, white blood cell and platelet issues. Most commonly used to evaluate for blood cancers and immature/abnormal white blood cell forms.
• When to Order
  • To further evaluate the etiology of cytopenic states (anemia, leukopenia, thrombocytopenia)
• Interpretation
  • RBC abnormalities
    • Fragmented cells (schistocytes, helmet cells)
      • Consider DIC, HUS, or TTP
    • Bite cells
      • Consider G6PD deficiency
    • Sickle cells
      • Sickle cell disease
    • Target cells
      • Consider liver disease, postsplenectomy states, or thalassemia
    • Reticulocytes
      • Premature cells indicated response to bleeding or hemolysis
    • Howell-Jolly bodies
      • Splenic absence or hypofunction.
  • WBC abnormalities
    • Blasts or tumor cells
      • Suggests underlying malignant hematologic disorder
    • Plasma cells
      • Suggests multiple myeloma or primary systemic amyloidosis
  • Platelet abnormalities
    • Large platelets
      • Consider DIC, TTP, HUS, or DITMA

Pearls

• Peripheral blood smears are inexpensive and have a quick turn around time. Maintain a low threshold for ordering this test in patients who present with cytopenic states.
• Blood smears can also be used to test for malaria. Consider this in febrile patients who have recently returned from tropical regions.

Deep Dive

• Peripheral Blood Film – A Review (PubMed)

Rapid Review

• Background
  • Measurement of phosphorus ion levels in the blood to evaluate the effects of certain disease states. Often useful for management of bone, parathyroid, and renal disease. 
• When to Order
  • Suspected calcium abnormalities
  • Diagnosis/monitoring of tumor lysis syndrome
  • Suspected rhabdomyolysis, sepsis, or DKA
• Interpretation
  • Reference Range
    • 3 – 4.5 mg/dL (adults)
    • 4.5 – 6.5 mg/dL (children)
    • 4.3 – 9.3 mg/dL (newborns)
  • Hypophosphatemia
    • Causes include vomiting, diarrhea, vitamin D deficiency, hyperparathyroidism, renal tubular damage, glucose/insulin administration
    • Levels < 1.5 mg/dL may cause hemolysis, muscle weakness, bone deformities, or coma. 
  • Hyperphosphatemia
    • Causes include CKD, renal failure, DKA, rhabdomyolysis, leukemia
    • Rapid elevations of phosphate can cause severe hypocalcemia (tetany, hypotension, seizures)

Pearls

• Phosphate and calcium levels are inversely related. As phosphate levels increase, calcium is decreased because phosphate binds to calcium and reduces the availability of free calcium in the blood.
• Phosphate levels have prognostic value in patients hospitalized for community acquired pneumonia. Patients with hypophosphatemia tend to have prolonged hospitalizations and increased mortality.

Deep Dive

• Utility of Calcium, Magnesium, and Phosphate Testing in the Emergency Department (PubMed)

Rapid Review

• Background
  • Thyroid-stimulating hormone (TSH) is a chemical released by the hypothalamus that directs the thyroid gland to produce additional hormones. This is used as a screening test for the evaluation and management of thyroid dysfunction.
• When to Order
  • Suspected hypothyroidism
    • Bradycardia, hypotension, constipation, fatigue/lethargy, depression, weight gain
  • Suspected hyperthyroidism
    • tachycardia, hypertension, nervousness, diarrhea, difficulty sleeping
• Interpretation
  • Normal Range
    • 0.5 – 5.0 microunits/mL (adults)
  • Low TSH
    • Consistent with hyperthyroidism
    • Graves disease, thyroiditis, thyroid cancer, drug induced (amiodarone, lithium, aspirin, iodine), or pituitary adenoma
  • High TSH
    • Consistent with hypothyroidism
    • Myxedema coma, thyroiditis, hashimoto disease, postsurgical, external radiation, infection, drugs (opiates)

Pearls

• TSH has a great sensitivity for both hypothyroidism and hyperthyroidism. In the majority of circumstances, a normal TSH effectively rules out both conditions.
• If the TSH is abnormal, a free T3/T4 should be sent to confirm. If your clinical suspicion is high, send them all at the same time.

Deep Dive

• Interpretation of Thyroid Studies in the Emergency Department (Taming the SRU)

Rapid Review

• Background
  • Troponins are protein molecules that can become elevated in the bloodstream following muscle breakdown in the heart. It is most commonly used to assess for evidence of myocardial injury, however it can also be elevated in cases of heart failure, renal disease, and other conditions. There are many types of troponins that can be measured, but a common type used in the emergency department is high sensitivity troponin I (hs-cTnI). Algorithms vary by department.
• When to Order
  • Suspicion for ACS 
• Interpretation (example of 1 algorithm for hs-cTnI)
  • <  4 ng/L
    • MI can be ruled out
  • 5 ng/L – 17 ng/L
    • Perform repeat troponin at 1 hour and 3 hours
    • If values  remain < 18,then MI can be ruled out
  • > 18 ng/L
    • Critical value for diagnosis of MI, if supported by clinical symptoms, EKG findings, or cardiac imaging results

Pearls

• An elevated troponin does not necessarily mean NSTEMI/STEMI.  Keep your differential open to other etiologies, such as pulmonary embolism, myocarditis, aortic dissection, stroke, and sepsis.
• Patients with chronic kidney disease often have a baseline elevation of troponin levels, presenting a diagnostic challenge. Be especially vigilant in this population.

Deep Dive

• High Sensitivity Cardiac Troponin T in a Multisite United States Cohort (REBEL EM)

Rapid Review

• Background
  • Uric acid is a byproduct of purine catabolism. The kidneys eliminate ⅔ of uric acid, while the GI tract excretes the other ⅓.  High uric acid levels can be seen in cancers and other lymphoproliferative disorders, as well as excess dietary intake. High levels chronically can lead to gout, in which uric acid crystals form in the joints.
• When to Order
  • Aid in the diagnosis of gout
  • Establishing etiology for kidney stones
  • Patient undergoing chemotherapy or radiation treatment
• Interpretation
  • Normal Range
    • Adult Male (4.0-8.5 mg/dL)
    • Adult Female (2.7-7.3 mg/dL)
    • Pediatric (2.5-5.5 mg/dL)
  • Elevated Uric Acid
    • Gout, elevated triglyceride levels, CKD/renal failure, anemia, hypothyroidism, dehydration, diuretics, excessive exercise, high purine diet
  • Decreased Uric Acid
    • SIADH, drugs (salicylates, probenecid, allopurinol, estrogen, indomethacin, phenothiazines), HIV infection, low purine diet

Pearls

• Uric acid levels are normal in approximately 63% of patients with acute gout attacks. A normal uric acid level does not exclude the disease.
• Excessive exercise and purine-rich diets (mussels, sardines, sweetbreads, bacon, turkey, scallops) can elevate uric acid levels. 

Deep Dive

• Uric Acid (Medscape)

Rapid Review

• Background
  • Urinalysis is a test that measures a number of parameters of the patient’s urine. This typically includes a gross visual examination (urine color/clarity), followed by a chemical examination (pH, specific gravity, glucose, ketones, nitrite, leukocyte esterase, bilirubin, proteins, blood), and finally a microscopic examination (WBCs, RBCs, epithelial cells, crystals, bacteria, yeast) 
• When to Order
  • Pain in abdomen/flank/pelvis
  • Altered mental status
  • Any urinary symptom
• Interpretation
  • Color
    • Normal range: (yellow)
    • Dark yellow urine may indicate dehydration
    • “Coca-cola” urine suspicious for rhabdomyolysis
    • Red urine may indicate hematuria, certain food/drug ingestions
  • Clarity/turbidity
    • Normal range (clear/cloudy)
    • Turbid urine indicates high amounts of material (casts, crystals, bacteria, proteinuria, or cellular debris)
  • pH
    • Normal range: (4.5-8.0)
    • Alkaline urine can be caused by UTI (proteus/klebsiella) or certain kidney stones (calcium oxalate/magnesium phosphate)
  • Specific gravity
    • Normal range: (1.005-1.025)
    • Elevated value may be due to dehydration or elevated proteins/ketoacids
    • Decreased value may indicate impaired urine concentrating ability (diabetes insipidus, ATN, or sickle cell nephropathy)
  • Glucose
    • Normal range: (<130 mg/d)
    • Elevated glucose commonly seen in diabetics and pregnancy
  • Ketones
    • Normal range: (None)
    • Presence of ketones may indicate dehydration, DKA, vomiting, starvation, or pregnancy
  • Nitrite
    • Normal range: (None)
    • Presence suggests gram negative bacteria. Likely UTI but cannot rule out if negative
  • Leukocyte Esterase
    • Normal range: (None)
    • Presence is 70% sensitive and 50% specific for detecting WBCs
  • Bilirubin
    • Normal range: (None)
    • Presence is associated with liver disease, hemolysis, or intestinal bacterial overgrowth
  • Protein
    • Normal range (<150 mg/d)
    • Transient elevated may be due to stress, fever, CHF, exercise, or seizure
    • Persistent elevation may be due to nephrotic syndrome, glomerulonephritis, ATN, AIN, or multiple myeloma
  • Blood
    • Normal range: (< 3 RBCs)
    • Presence indicates blood, though cannot differentiate from where in the urinary tract.
  • WBCs
    • Normal range: (<2-5 WBCs/hpf)
    • Presence indicates infection, inflammation, or contamination. Usually suggestive of urinary tract infection.
  • RBCs
    • Normal range: (<2 RBCs/hpf)
    • Presence may indicate kidney stones, pyelonephritis, UTI, cancer,foley trauma, or anticoagulants
  • Epithelial Cells
    • Squamous cells (when more than 15-20) indicates contaminated sample
    • Hyaline casts are non-specific
    • White cell casts suggests vaginal infection, acute pyelonephritis, or tubulointerstitial nephritis
    • Muddy-brown casts diagnostic for acute tubular necrosis (ATN)
    • Waxy and broad casts suggest advanced renal failure
    • Fatty casts suggest nephrotic syndrome
  • Crystals
    • Calcium oxalate = ethylene glycol ingestion
    • Uric acid = gout or tumor lysis syndrome
    • Cystine crystals = cystinuria
    • Magnesium phosphate = UTI caused by klebsiella or proteus
  • Bacteria
    • Normal range: (None)
    • Presence indicates infection or contamination. Correlate clinically and with other findings (nitrites, leukocyte esterase, etc.)
  • Yeast
    • Normal range: (None)
    • Presence indicates contamination or yeast infection. Correlate clinically.

Pearls

• If hemoglobin is present in a female’s urine sample, be sure to ask about possible contamination from menstrual cycle. 
• U-Bag (perineal bag) specimens have high contamination rates (up to 50%). Avoid using them for urinalysis/urine culture when able. 

Deep Dive

• Urinalysis/Urine Dipstick Components (emDocs)

Rapid Review

• Background
  • Urine cultures are used to detect the presence and type of bacteria in the urine.  They can also be used to test the susceptibility of different antibiotics. Takes 48 hours for final results.
• When to Order
  • Complex UTI’s (males, recent antibiotic therapy, pyelonephritis, instrumentation)
• Interpretation
  • Negative
    • No growth in 24-48 hours
  • Positive
    • Positive growth of single bacteria (> 100,000 CFUs/mL) highly suggestive of UTI
    • Most commonly E. coli (80%). Others include Staphyylococcus saprophyticus (5-15%), klebsiella, enterobacter, or proteus

Pearls

• Growth of 2 or more bacteria is likely due to contamination
• If urine specimens are left at room temperature for >2 hours, there is a high likelihood of false-positives due to contaminants

Deep Dive

• Evaluating the Impact of a Urinalysis to Reflex Culture Process Change in the Emergency Department at VA Hospital (PubMed)

Rapid Review

• Background
  • The urine toxicology screen is used to detect the presence of multiple drugs in the patient’s urine, including cocaine, cannabinoids, amphetamines, opiates, phencyclidine, and benzodiazepines. 
• When to Order
  • Unexplained AMS
• Interpretation
  • Cocaine
    • 2-4 day duration of detectability
    • High accuracy. False positives are rare
  • Cannabinoids
    • 3 day duration of detectability. Up to 30 days for long-term users.
    • Fairly accurate
    • Synthetic cannabinoids or passive inhalation will not typically cause positive screen
  • Amphetamines
    • 48 hour duration of detectability
    • Many medications (cold/flu medications, herbals) may cause false positive
  • Opiates
    • 2-4 day duration of detectability, depending on substance
    • Synthetic opiates (fentanyl/oxycodone) may not be detected.
  • Benzodiazepines
    • 3-30 day duration of detectability, depending on substance
    • Low false positive rate. 25-30% false negative rate
  • Phencyclidine (PCP)
    • 8 day duration of detectability
    • High false positive rate (structurally similar to many medications like diphenhydramine, bupropion, venlafaxine, dextromethorphan, ketamine, etc.)

Pearls

• Urine tox screens may be useful for altered pediatric patients or trauma patients in need of substance abuse counseling. However, ACEP does not recommend urine drug screening in cooperative adults with psychiatric symptoms, as it rarely affects ED management.
• Urine tox screens have high rates of both false positive and false negative results. Be careful ordering this test, as results can have profound social implications, including family relationships, reputation, sports participation, and legal convictions.

Deep Dive

• TOXCard: Urine Drug Screens (emDocs)