Laboratory evaluation of urea cycle disorders

The urea cycle disorders (UCDs) represent a group of inherited metabolic di seases with hyperammonemia as the primary laboratory abnormality Affected i ndividuals may become comatose or die if not treated rapidly. Diagnosis of a UCD requires a high index of suspicion and judicious use of the laborator y. It is important to rule out other conditions causing hyperammonemia that may require different treatment. The astute clinician may suspect a specif ic UCD in the appropriate clinical setting, but only laboratory results can confirm a specific diagnosis. The importance of the laboratory in helping the clinician to differentiate among various causes of hyperammonemia, in c onfirming a specific UCD, in carrier testing, and in prenatal diagnostic te sting is highlighted in this review.