Laboratory evaluation for suspected inborn errors of metabolism

	Comments
Initial evaluation*
Blood tests
CBC with differential
Blood glucose
Electrolytes, BUN, creatinine, uric acid
Arterial blood gas
Plasma ammonia	Should be obtained from artery or vein without a tourniquet. The tube should be placed on ice for transport to the laboratory and analyzed immediately. If the plasma ammonia concentration is >100 micromol/L (1.7 mcg/mL), the measurement should be repeated immediately.
AST, ALT, bilirubin, PT	If the patient has signs of liver disease.
LDH, aldolase, creatine kinase
Urine tests
Color, odor
Urinalysis
Reducing substances
Myoglobin	If the patient has signs or symptoms of myopathy.
Specialized tests
Blood tests
Quantitative plasma amino acids	Plasma amino acid analysis must be performed quantitatively rather than qualitatively.
Lactate and pyruvate	Lactate and pyruvate should be measured in arterial blood and transported on ice.
Acylcarnitine profile	Analysis of acylcarnitine conjugates is performed by tandem mass spectrometry and can be measured in a plasma sample or a filter-paper bloodspot. Serum is preferred because of inherent problems in quantitating compounds from a filter-paper blood spot
Urine tests
Qualitative urine organic acids	Minimum of 2 to 5 mL in sterile container without preservative.
Additional tests in selected patients
Creatine/guanidinoacetate
Purine pyrimidine panel
Very-long-chain fatty acid profile
Alpha aminoadipic semialdehyde

CBC: complete blood count; BUN: blood urea nitrogen; AST: aspartate aminotransferase; ALT: alanine aminotransferase; PT: prothrombin time; LDH: lactate dehydrogenase.
* If possible, blood and urine samples should be obtained for both the initial and specialized tests at the time of presentation. Samples for specialized tests should be processed and stored appropriately for further testing if indicated.

Graphic 67745 Version 10.0

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Laboratory evaluation for suspected inborn errors of metabolism