Test Laboratory abnormality metabolic diseases a Indications, comments Aminoacidopathies Organic acidemias Tandem mass spectrometry, requires minimum mL blood, mL ideal b , heparin, or EDTA tube Obtain if metabolic catastrophe, neurologic, cardiac, GI/hepatic, musculoskeletal, psychiatric symptoms suggestive of possible IEM, metabolic acidosis, elevated anion gap, hypoglycemia, inappropriate ketonuria, hyperammonemia Blood Amino acids— quantitative (plasma or serum) Urea cycle defects Mitochondrial disorders Acylcarnitine profile (plasma or serum) Organic acidemias Fatty acid oxidation defects Mitochondrial disorders Primary carnitine deficiency Lactate, pyruvate Disorders of carbohydrate (deproteinized blood) utilization Mitochondrial disorders Carnitine deficiency may be due to primary defect in carnitine or carnitine transporter, or secondary due to organic acidemia or fatty acid oxidation defect; can also occur in normal children during dehydration Free and total carnitine may also be helpful if carnitine deficiency is suspected Samples must be free flow, deproteinized at bedside—1 mL into tubes with 2-mL perchloric or trichloroacetic acid, transport on ice Evaluate lactate, pyruvate, and ratio Lactate also increased in patient with hypoxia, poor perfusion, sepsis Urine Organic acids Aminoacidopathies Organic acidemias Fatty acid oxidation defects Mitochondrial disorders Peroxisomal disorders Acylglycines Organic acidemias Fatty acid oxidation defects Orotic acid Urea cycle defects (ornithine transcarbamylase deficiency) Urine best source for organic acids, minimum 2–5 mL, 10–20 mL ideal without preservative c Obtain if metabolic catastrophe, neurologic, cardiac, GI/hepatic, musculoskeletal, psychiatric, symptoms suggestive of possible IEM, metabolic acidosis, elevated anion gap, hypoglycemia, inappropriate ketonuria, hyperammonemia Should be performed only in conjunction with serum or plasma carnitines, minimum 2–5 mL without preservative c Send if hyperammonemia, minimum mL without preservative Cerebrospinal fluid Glucose, protein, lactate, Aminoacidopathies pyruvate, glycine, Organic acidemias serine, alanine, 1–4 mL, freeze −20°C or −70°C