Amino Acid Analysis, Plasma (Quest Diagnostics)

Amino Acid analysis is necessary for the diagnosis of a variety of inborn errors of metabolism. These include, but are not limited to:

- phenylketonuria

- tyrosinemia

- citrullinemia

- non-ketotic hyperglycinemia

- maple syrup urine disease

- and homocystinuria.

The assay is also key for the continued monitoring of treatment plans for these disorders and useful for assessing nutritional status of patients.

Interpretive Information:

Elevation of 1 or more amino acids may be diagnostic of an aminoacidopathy. Elevated amino acid levels are also associated with noninherited diseases such as severe liver disease and renal tubular disorders (eg, Fanconi syndrome).

Decreased levels of amino acids are associated with malnutrition as seen in the elderly or those with poor protein intake or gastrointestinal disease.

Additional laboratory testing is required to diagnose other inherited disorders (ie, lactic acidosis, organic aciduria, and some urea cycle defects). Results should be evaluated in the context of clinical findings and/or additional test results.

Infant formulas that are supplemented with amino acids (particularly methionine and homocitrulline) and parenteral nutrition may affect the clinical accuracy of this test. Bacterial contamination of specimens and certain medications, such as valproic acid, can also affect the levels of specific amino acids. In addition, the absence of a protein-containing diet in newborns may preclude detection of selected aminoacidopathies.


Part 8. Amino Acids. In: Scriver CR, Beaudet AL, Valle D, Sly WS, Childs B, Kinzler KW, Vogelstein B, eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York, NY: McGraw-Hill, Inc; 2001;1665-2105.

Part IV. Disorders of amino acid metabolism and transport. Fernandes J, Saudubray J-M, Van den Berghe G, eds. Inborn Metabolic Diseases Diagnosis and Treatment. 3rd ed. New York, NY: Springer; 2000;169-273.

Part 2. Disorders of amino acid metabolism. Nyhan WL, Barshop BA, Ozand PT, eds. Atlas of Metabolic Diseases. 2nd ed. New York, NY: Oxford University Press Inc; 2005;109-189.

Blau N, Duran M, Blaskovics ME, Gibson KM, eds. Physician's Guide to the Laboratory Diagnosis of Metabolic Diseases. 2nd ed. New York, NY: Springer; 2003.

Heiblim DI, Evans HE, Glass L, et al. Child neurology: amino acid concentrations in cerebrospinal fluid. Arch Neurol. 1978;35:765-768.

Goldsmith RF, Earl JW, Cunningham AM. Determination of delta-aminobutyric acid and other amino acids in cerebrospinal fluid of pediatric patients by reversed-phase liquid chromatography. Clin Chem. 1987;33:1736-1740.


Optimal range: 0 - 47 umol/L


Optimal range: 2 - 9 umol/L


Optimal range: 200 - 483 umol/L

Alpha Aminoadipic Acid

Optimal range: 0 - 2 umol/L

Alpha Aminobutyric Acid

Optimal range: 7 - 32 umol/L


Optimal range: 43 - 107 umol/L

Arginine is found in all protein foods and is very abundant in seeds and nuts. It is considered a semi-essential amino acid during early development, infection/inflammation, or renal and/or intestinal impairment.



Optimal range: 31 - 64 umol/L

Asparagine is a non-essential protein amino acid that is present in many fruits and vegetables including asparagus, from which it gets its name. Other dietary sources include meat, potatoes, eggs, nuts, and dairy. It can also be formed from aspartic acid and glutamine using the enzyme asparagine synthetase.

In addition to being a structural component of many proteins, asparagine is also useful to the urea cycle. It acts as a nontoxic carrier of residual ammonia to be eliminated from the body. Asparagine is rapidly converted to aspartic acid by the enzyme asparaginase. Interestingly, L-asparaginase has been successfully used as a chemotherapeutic agent for decades.

It causes extracellular depletion of asparagine which seems to play a critical role in cellular adaptations to glutamine and apoptosis.


Aspartic Acid

Optimal range: 1 - 4 umol/L

Beta Aminoisobutyric Acid

Optimal range: 0 - 3 umol/L

Beta-aminoisobutyric acid (also known as 3-aminoisobutyric acid) is a non-protein amino acid formed by the catabolism of valine and the nucleotide thymine. It is further catabolized to methylmalonic acid semialdehyde and propionyl-CoA. Levels are controlled by a vitamin B6-dependent reaction in the liver and kidneys. β-aminoisobutyric acid can also be produced by skeletal muscle during physical activity.



Optimal range: 0 - 5 umol/L


Optimal range: 16 - 51 umol/L


Optimal range: 0 - 1 umol/L

Cystathionine is an intermediate dipeptide within the process of transsulfuration. Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle. Currently, there is no known source or physiologic function for cystathionine other than serving as a transsulfuration intermediate. Some literature suggests that cystathionine may exert protection against endoplasmic reticulum stress-induced tissue damage and cell death, but studies are sparse.



Optimal range: 5 - 13 umol/L

Gamma Aminobutyric Acid

Optimal range: 0 - 3 umol/L

Glutamic Acid

Optimal range: 10 - 97 umol/L


Optimal range: 428 - 747 umol/L


Optimal range: 122 - 322 umol/L


Optimal range: 0 - 0 umol/L


Optimal range: 60 - 109 umol/L


Optimal range: 0 - 1 umol/L

Hydroxyproline, Plasma

Optimal range: 4 - 27 umol/L


Optimal range: 34 - 98 umol/L


Optimal range: 73 - 182 umol/L


Optimal range: 119 - 233 umol/L

Lysine is a nutritionally essential amino acid abundant in meat, fish, fowl, and legumes and is needed for formation of body proteins and enzymes.

Lysine can be methylated using S-adenosylmethionine (SAM) to synthesize carnitine, which is needed for fatty acid oxidation. Lysine also generates Acetyl CoA for use in the citric acid cycle. Lysine, proline, hydroxyproline, and vitamin C are important in the synthesis of collagen for skin, bones, tendons and cartilage.



Optimal range: 16 - 34 umol/L


Optimal range: 27 - 83 umol/L


Optimal range: 40 - 74 umol/L

Phenylalanine is an essential amino acid found in most foods which contain protein such as meat, fish, lentils, vegetables, and dairy. Phenylalanine is the precursor to another amino acid, tyrosine. Because tyrosine is needed to form several neurotransmitters (dopamine, epinephrine, and norepinephrine), as well as thyroid hormone and melanin, phenylalanine intake is important.



Optimal range: 104 - 383 umol/L


Optimal range: 0 - 4 umol/L


Optimal range: 65 - 138 umol/L


Optimal range: 31 - 102 umol/L


Optimal range: 67 - 198 umol/L


Optimal range: 40 - 91 umol/L


Optimal range: 38 - 96 umol/L


Optimal range: 132 - 313 umol/L