What labs should be ordered for a patient suspected of having heat stroke?

Laboratory Tests for Heat Stroke Patients

For patients with suspected heat stroke, comprehensive laboratory testing should include complete blood count, comprehensive metabolic panel, creatine kinase, coagulation studies, arterial blood gases, and urinalysis to assess for multi-organ dysfunction and guide management.

Core Laboratory Tests for All Heat Stroke Patients

Heat stroke is a medical emergency characterized by core body temperature above 40°C (104°F) with associated central nervous system dysfunction. Prompt laboratory evaluation is critical to assess severity and guide management.

Essential Laboratory Tests:

• Complete Blood Count (CBC)

  • Evaluates for thrombocytopenia, which occurs in up to 75.7% of heat stroke patients 1
  • Assesses for leukocytosis indicating systemic inflammatory response

• Comprehensive Metabolic Panel

  • Electrolytes (sodium, potassium, chloride)
    • Hyponatremia is common (78.4% of cases) 1
    • Hypokalemia may be present (significant difference compared to controls) 1
  • Renal function tests (BUN, creatinine)
    • Identifies acute kidney injury from rhabdomyolysis
  • Glucose
    • Hypoglycemia can mimic neurological symptoms of heat stroke
  • Liver function tests (AST, ALT)
    • Elevated in 70-78% of heat stroke patients 1
    • AST elevation is more pronounced than ALT in heat stroke 1

• Creatine Kinase (CK)

  • Critical for diagnosing rhabdomyolysis
  • Abnormal in 70.3-81.1% of cases 1
  • Elevated CK (>1000 IU/L) strongly correlates with multi-organ dysfunction 2

• Coagulation Studies

  • PT/INR, aPTT, fibrinogen, D-dimer
  • D-dimer elevated in 70.3% of cases 1
  • Identifies disseminated intravascular coagulation (DIC), a common complication

• Arterial Blood Gas Analysis

  • Evaluates acid-base status
  • Metabolic acidosis present in 81% of heat stroke patients 3
  • Respiratory alkalosis in 55% of cases 3
  • Abnormal PaCO₂ in 70.3% of patients 1

• Cardiac Markers

  • Troponin I (TnI)
    • Abnormal in 73% of heat stroke patients 1
  • Lactate dehydrogenase (LDH)
    • Elevated in 81.1% of cases 1

• Urinalysis

  • Evaluates for myoglobinuria
  • Assesses hydration status and renal function

Additional Tests Based on Clinical Presentation

• Toxicology Screen

  • For patients with altered mental status
  • Rules out substance use that may predispose to heat stroke

• Blood Cultures

  • If infection is suspected as contributing factor
  • Differentiates between heat stroke and sepsis

• Phosphate Level

  • Hypophosphatemia may develop during recovery phase 4

Monitoring Parameters

• Serial CK Measurements

  • Monitor trend as CK typically continues to rise after admission 1
  • Peak CK correlates with severity of rhabdomyolysis

• Serial Platelet Counts

  • Progressive thrombocytopenia indicates worsening DIC 1

• Repeat Electrolytes

  • Monitor during fluid resuscitation to prevent iatrogenic disturbances

Clinical Implications

The laboratory abnormalities in heat stroke reflect multi-organ dysfunction, with metabolic acidosis, elevated CK, and liver enzyme abnormalities being the strongest predictors of poor outcomes 2. Early identification of these abnormalities allows for targeted interventions to prevent complications.

Common Pitfalls to Avoid

• Delaying laboratory testing while focusing solely on cooling measures
• Overlooking coagulation studies which can identify early DIC
• Failing to monitor CK trends which continue to rise after initial presentation
• Not repeating laboratory tests as abnormalities may develop or worsen over time
• Missing hyponatremia which can contribute to neurological symptoms

Prompt laboratory evaluation combined with aggressive cooling measures and supportive care significantly improves outcomes in heat stroke patients.