What is the role of lab testing in the workup of Reye syndrome?

Updated: Apr 02, 2018
  • Author: Debra L Weiner, MD, PhD; Chief Editor: Kirsten A Bechtel, MD  more...
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An ammonia level as high as 1.5 times normal 24-48 hours after the onset of mental status changes is the most frequent laboratory abnormality. Ammonia tends to peak 56-60 hours after the onset of symptoms. The ammonia level may return to normal in stages 4 and 5.

Liver function tests

Levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) increase to 3 times normal but may return to normal by stages 4 or 5. Bilirubin levels are higher than 2 mg/dL (but usually lower than 3 mg/dL) in 10-15% of patients. If the direct bilirubin level is more than 15% of total or if the total bilirubin level exceeds 3 mg/dL, consider other diagnoses.

Lipase and amylase levels are elevated. The serum bicarbonate level is decreased secondary to vomiting. Blood urea nitrogen (BUN) and creatinine levels are elevated.

Lactic dehydrogenase (LDH) 

LDH may be high or low.


While glucose is usually normal, it may be low, particularly during stage 5 and in children younger than 1 year.

Electrolytes, blood urea nitrogen (BUN), creatinine

Sodium may be low due to syndrome of inappropriate antidiuretic hormone (SIADH) or elevated due to diabetes insipidus (DI). Serum bicarbonate is usually decreased due to vomiting. BUN and creatinine are usually elevated.  Anion gap is usually elevated due to metabolic acidosis.

Coagulation studies

Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are prolonged more than 1.5-fold in more than 50% of patients. Levels of factors I (fibrinogen), II, VII, IX, and X may be low because of the disruption of synthetic activities in the liver. Consumption may also contribute to low levels of coagulation factors. Platelet counts are usually normal.

Fatty acids, amino acids

Levels of free fatty acids and amino acids (eg, glutamine, alanine, and lysine) may be elevated.

Blood gas

Venous blood gas should be obtained to evaluate for metabolic acidosis.


Urine specific gravity is increased; 80% of patients have ketonuria.

Cerebral spinal fluid (CSF)

CSF WBC count, by disease definition, does not exceed 8 cells/µL. Opening pressure is usually normal but may be elevated, particularly in stages 3-5.

Recognize that these derangements are not specific for Reye syndrome and may suggest other etiologies that should be considered.

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