Distinguishing biochemical findings of inborn errors of metabolism*

-: usually absent; ±: sometimes present; +: usually present; ++: always present; A: appropriate production of ketones for the degree of hypoglycemia (eg, ketones are appropriately absent in peroxisomal disorders because hypoglycemia is not a feature of these disorders); H: inappropriately high (eg, 4+ ketones are inappropriately high in the setting of a normal glucose level); L: inappropriately low (eg, ketones are inappropriately low if the blood glucose is <20 mg/dL and the urine ketones are only 1+ or 2+ because they should be significantly elevated in the setting of such extreme hypoglycemia).
* Within disease categories, not all diseases have all findings; for disorders with episodic decompensation, clinical and laboratory findings may be present only during acute crisis; for progressive disorders, findings may not be present early in the course of disease.