Amino acid levels

Amino acid	High in plasma	Low in plasma	High in urine
Alanine	Disorders of pyruvate metabolism, urea cycle disorders, mitochondrial disorders	Untreated maple syrup urine disease	Disorders of pyruvate metabolism, urea cycle disorders, mitochondrial disorders
Alloisoleucine	Maple syrup urine disease	–	Maple syrup urine disease
Arginine	Argininemia	Argininosuccinic aciduria, citrullinemia, ornitine transcarbamylase deficiency, carbamylphosphatase deficiency, inadequate diet	Argininemia, cystinuria, lysinuric protein intolerance
Argininosuccinate	Argininosuccinic aciduria	–	Argininosuccinic aciduria
Aspartate	–	–	–
Citrulline	Citrullinemia, citrin deficiency, argininosuccinic aciduria	Ornitine transcarbamylase deficiency, carbamylphosphatase deficiency, inadequate diet	Citrullinemia, citrin deficiency, argininosuccinic aciduria
Cystine	–	Molybdenum cofactor deficiency/sulfate oxidase deficiency	Cystinuria
Glutamate	Improper sample handling	–	–
Glutamine	Urea cycle disorders/hyperammonemia	Improper sample handling	–
Glycine	Glycine encephalopathy, organic acidemias	–	Glycine encephalopathy, organic acidemias
Histidine	Histidinemia (benign condition)	–	Histidinemia (benign condition)
Homocystine (free)	Homocystinuria, disorders of vitamin B12 transport and synthesis	–	Cystathionine beta-synthetase deficiency, disorders of vitamin B12 transport and synthesis
Isoleucine	Maple syrup urine disease, fasting	–	Maple syrup urine disease
Leucine	Maple syrup urine disease, fasting	–	Maple syrup urine disease
Lysine	Citrin deficiency, hyperlysinemia (benign)	–	Cystinuria, lysinuric protein intolerance
Methionine	Homocystinuria, citrin deficiency, liver dysfunction	Disorders of vitamin B12 transport and synthesis	Cystathionine beta-synthetase deficiency, liver dysfunction
Ornithine	Ornitine aminotransferase deficiency, hyperornithinemia-hyperammonemia-homocitrullinemia (HHH) syndrome	–	Cystinuria, lysinuric protein intolerance, ornithine aminotransferase deficiency
Phenylalanine	Phenylketonuria	–	Phenylketonuria
Proline	Hyperprolinemia	–	Hyperprolinemia
Serine	–	3-phosphoglycerate dehydrogenase deficiency	–
Threonine	Citrin deficiency	–	–
Tryptophan	–	–	–
Tyrosine	Tyrosinemia types I and II, hepatic dysfunction	Phenylketonuria	Tyrosinemia types I and II, hepatic dysfunction
Valine	Maple syrup urine disease, fasting	–	Maple syrup urine disease

Patterns of abnormalities:

Argininemia - elevated plasma arginine
Argininosuccinic aciduria - elevated plasma citrulline, elevated plasma argininosuccinate, low plasma arginine
Carbamyl phosphate synthetase deficiency - low plasma citrulline, ±elevated plasma glutamine (identical pattern to ornithine transcarbamylase deficiency)
Citrin deficiency - elevated plasma citrulline, threonine, methionine, lysine, and arginine
Citrullinemia - elevated plasma citrulline, low plasma arginine
Cystinuria - elevated urine cystine, lysine, arginine, and ornithine
Glycine encephalopathy - cerebrospinal fluid (CSF):plasma glycine ratio >0.08
HHH syndrome - elevated plasma ornithine
Homocystinuria - elevated plasma homocystine* and methionine
Hyperprolinemia - elevated plasma proline
Lysinuric protein intolerance - elevated urine lysine, arginine, and ornithine
Maple syrup urine disease - elevated plasma alloisoleucine, isoleucine, leucine, and valine with perturbation of the normal 1:2:3 ratio of isoleucine:leucine:valine, low plasma alanine
Ornithine aminotransferase deficiency - elevated plasma ornithine
Ornithine transcarbamylase deficiency - low plasma citrulline, ± elevated plasma glutamine (identical pattern to carbamyl phosphate synthetase deficiency)
Phenylketonuria - elevated plasma phenylalanine ± low plasma tyrosine
Tyrosinemia types I and II - elevated plasma tyrosine
Vitamin B12 (cobalamin) processing disorders - elevated plasma homocystine* with low or normal plasma methionine

* Routine plasma amino acid analysis measures free plasma homocystine, not total plasma homocystine. Total plasma homocystine is the preferred test for the diagnosis and management of homocystinuria and disorders of vitamin B12 (cobalamin) transport and synthesis.

Courtesy of V Reid Sutton, MD.

Graphic 73440 Version 7.0

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Amino acid levels