Table 1. Routine laboratory tests that should be always ordered when an IEM is suspected.

Test

Complete blood count with differential

Liver function tests

Renal function tests

*Ammonia

Blood gases

Anion gap

Glucose

Lactate

Urine and blood ketones

This table represents the most useful routine laboratory tests when suspecting an IEM in a patient with a metabolic stress state. Results of these tests may indicate the underlying pathophysiology and narrow the focus of additional testing to identify a metabolic disorder or category of disorders. *, red blood cells can produce and release ammonia into standing blood specimen. In addition, enzymes in blood can deaminate amino acids causing elevation of ammonia. Therefore, measurement of ammonia can be challenging. A free-flowing blood sample should be collected into preferable pre-chilled tubes. The sample should be transported on ice to the laboratory and separated as soon as possible, preferably within 15 minutes. Specimen should be analyzed as soon as possible. IEM, inborn errors of metabolism.