Heat Stroke Workup

Updated: Jul 20, 2022
  • Author: Robert S Helman, MD; Chief Editor: Joe Alcock, MD, MS  more...
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Laboratory Studies

Arterial blood gas testing

Arterial blood gas analysis may reveal respiratory alkalosis due to direct central nervous system (CNS) stimulation and metabolic acidosis due to lactic acidosis. Hypoxia may be due to pulmonary atelectasis, aspiration pneumonitis, or pulmonary edema.

Lactic acidosis

Lactic acidosis commonly occurs following exertional heat stroke (EHS) but may signal a poor prognosis in patients with classic heat stroke.


Hypoglycemia may occur in patients with EHS and in patients with fulminant hepatic failure.



Hypernatremia due to reduced fluid intake and dehydration commonly is observed early in the course of disease but may be due to diabetes insipidus. Hyponatremia is observed in patients using hypotonic solutions, such as free water, and in patients using diuretics. It also may be due to excessive sweat sodium losses.


Hypokalemia is common in the early phases of heat stroke, and deficits of 500 mEq are not unusual. However, with increasing muscle damage, hyperkalemia may be observed.


Hypophosphatemia secondary to phosphaturia and hyperphosphatemia secondary to rhabdomyolysis, hypocalcemia secondary to increased calcium binding in damaged muscle, and hypomagnesemia also are observed commonly.

Hepatic function tests

Hepatic injury is a consistent finding in patients with heat stroke.

Aminotransferase (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]) llevels commonly rise to the tens of thousands during the early phases of heat stroke and peak at 48 hours, but they may take as long as 2 weeks to peak.

Jaundice may be striking and may be noted 36-72 hours after the onset of liver failure.

Muscle function tests

Creatinine kinase (CK), lactate dehydrogenase (LDH), aldolase, and myoglobin commonly are released from muscles when muscle necrosis occurs.

CK levels exceeding 100,000 IU/mL are common in patients with EHS.

Elevations in myoglobin may not be noted despite muscle necrosis because myoglobin is metabolized rapidly by the liver and excreted rapidly by the kidneys.

Complete blood cell count

Elevated white blood cell counts commonly are observed in patients with heat stroke, and levels as high as 40,000/μL have been reported. Platelet levels may be low.

Renal function tests

Elevations in serum uric acid levels, blood urea nitrogen, and serum creatinine are common in patients whose course is complicated by renal failure.


Remember that urinary benzidine dipsticks do not differentiate between blood, hemoglobin, and myoglobin. Urine dipstick analyses that are positive for blood must be followed by a microscopic urinalysis to determine the presence or absence of red blood cells. Proteinuria also is common.

Cerebrospinal fluid analysis

Cerebrospinal fluid (CSF) cell counts may show a nonspecific pleocytosis, and CSF protein levels may be elevated as high as 150 mg/dL.


Myoglobin causes a reddish brown discoloration of the urine but does not affect the color of plasma. This is in contrast to hemoglobin, which causes discoloration of both plasma and urine.



Procedures may include the following:

  • Endotracheal intubation

  • Pulmonary artery catheter insertion

  • Central venous line insertion

  • Nasogastric tube insertion

  • Compartment pressure measurements

  • Fasciotomy

  • Thoracostomy

  • Peritoneal lavage

  • Hemodialysis