What laboratory tests should be ordered for a patient presenting with hypothermia?

Laboratory Tests for Patients Presenting with Hypothermia

For patients presenting with hypothermia, a comprehensive laboratory panel should include coagulation studies, complete blood count, metabolic panel, and arterial blood gases to assess for associated complications and guide management.

Core Laboratory Tests

• Core temperature measurement: Use the most accurate method available - intravascular, esophageal, or bladder thermistor provides the most accurate readings, followed by rectal, oral, and tympanic membrane measurements in that order 1
• Coagulation studies: PT/APTT to assess for hypothermia-induced coagulopathy, as a 1°C drop in temperature is associated with a 10% drop in coagulation factor function 1
• Complete blood count (CBC): To assess for anemia and monitor potential effects on blood cell counts, including platelet count which should be maintained above 50×10^9/l in patients with ongoing bleeding 1
• Comprehensive metabolic panel:
  • Electrolytes to assess for metabolic derangements 2
  • Liver and kidney function tests to monitor organ function 1
  • Blood glucose to rule out hypoglycemia as a cause or complication 3
• Arterial blood gases: To assess for metabolic acidosis, which is a common complication in hypothermic patients 3

Additional Tests Based on Clinical Presentation

• Cardiac biomarkers and ECG: To assess for myocardial injury, as hypothermia can cause cardiac dysfunction and arrhythmias 4
• Lactate levels: To assess tissue perfusion and severity of shock 1
• Toxicology screen: To rule out drug or alcohol intoxication as contributing factors, as these can accelerate heat loss 5
• Creatine kinase: To assess for rhabdomyolysis, which can occur in severe hypothermia 4

Important Considerations for Laboratory Testing

• Temperature correction: Coagulation tests (PT and APTT) should be performed at the patient's actual body temperature rather than the standard 37°C to accurately assess coagulopathy 1
• Timing of tests: Initial labs should be drawn before aggressive rewarming to establish baseline values 2
• Repeat testing: Laboratory tests should be repeated during rewarming to monitor for complications and guide management 6

Common Pitfalls and Caveats

• False normal coagulation tests: Standard coagulation tests performed at 37°C may appear normal despite significant coagulopathy at the patient's actual lower body temperature 1
• Misdiagnosis based on clinical presentation: Clinical symptoms may not correlate with core temperature severity; diagnosis and treatment should always be based on measured core temperature rather than clinical presentation alone 4
• Inadequate temperature measurement: Axillary measurements, temporal artery estimates, and chemical dot thermometers should not be used in critically ill hypothermic patients due to inaccuracy 1
• Overlooking secondary causes: Laboratory evaluation should include tests to identify potential underlying causes of hypothermia such as sepsis, endocrine disorders, or metabolic derangements 2, 3

Management Implications Based on Laboratory Findings

• Coagulopathy: If coagulation studies are abnormal, warming to normothermia is the primary treatment, as hypothermia-induced coagulopathy resolves with rewarming 1
• Acidosis: If metabolic acidosis is present, it typically improves with rewarming and should not be aggressively treated with bicarbonate unless severe 3
• Electrolyte abnormalities: Should be corrected gradually during rewarming to avoid complications 6