No other laboratory test can substitute for this measurement, nor will any suggest the need for it. Only clinical suspicion will indicate need. Certain primary genetic causes can be suspected on the basis of specific increases in amino acid levels, such as increased citrulline or argininosuccinic acid. By contrast, severe liver disease tends to cause a generalized increase in plasma amino acids. This test can help identify increases in such intermediates as propionic acid, methylmalonic acid, isovaleric acid, or other organic acids and point the way to diagnosis.
Blood lactate is useful in ruling out mitochondrial diseases.
Blood gases Patients with urea cycle disorders may be alkalotic due to stimulation of the respiratory drive by ammonia. Patients with urea cycle disorders are rarely acidotic. Severe refractory acidosis suggests organic acid disorder or mitochondrial disorder. Initial management should consist of cessation of protein intake with provision of as many nonprotein calories as practical, by intravenous or oral routes, or both if possible. More specific therapy depends on the etiology of the hyperammonemia.