Plasma amino acids is a screening test done on infants that looks at the amounts of amino acids in the blood. Amino acids are the building blocks for proteins in the body.

See also:

• Amino acids - urine
• Inborn errors of metabolism
• Newborn screening tests

A blood sample is needed. The area (usually the heel) is cleansed with germ-killing solution, and the skin is punctured with a sharp needle or a lancet. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The blood sample is sent to a lab. Chromatography is used to determine the amino acids levels in the blood.

The baby should not be fed for 4 hours before the test.

See also: Test/procedure preparation - infant

The needle stick will probably cause the infant to cry.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is done to measure the level of amino acids in the blood.

An increased level of a particular amino acid is a strong sign that there is a problem with the body's ability to break down (metabolize) that amino acid.

The test may also be used to look for decreased levels of amino acids in the blood, which may occur with fevers, inadequate nutrition, and certain medical conditions.

All measurements are in micromole per liter (micro mol/L). Normal values may vary between different laboratories. Talk to your doctor about your specific test results.

• Alanine
  • Children: 200 to 450
  • Adults: 230 to 510
• Alpha-aminoadipic acid
  • Children: not measured
  • Adults: not measured
• Alpha-amino-N-butyric acid
  • Children: 8 to 37
  • Adults: 15 to 41
• Arginine
  • Children: 44 to 120
  • Adults: 13 to 64
• Asparagine
  • Children: 15 to 40
  • Adults: 45 to 130
• Aspartic acid
  • Children: 0 to 26
  • Adults: 0 to 6
• Beta-alanine
  • Children: 0 to 49
  • Adults: 0 to 29
• Beta-amino-isobutyric acid
  • Children: not measured
  • Adults: not measured
• Carnosine
  • Children: not measured
  • Adults: not measured
• Citrulline
  • Children: 16 to 32
  • Adults: 16 to 55
• Cystine
  • Children: 19 to 47
  • Adults: 30 to 65
• Glutamic acid
  • Children: 32 to 140
  • Adults: 18 to 98
• Glutamine
  • Children: 420 to 730
  • Adults: 390 to 650
• Glycine
  • Children: 110 to 240
  • Adults: 170 to 330
• Histidine
  • Children: 68 to 120
  • Adults: 26 to 120
• Hydroxyproline
  • Children: 0 to 5
  • Adults: not measured
• Isoleucine
  • Children: 37 to 140
  • Adults: 42 to 100
• Leucine
  • Children: 70 to 170
  • Adults: 66 to 170
• Lysine
  • Children: 120 to 290
  • Adults: 150 to 220
• Methionine
  • Children: 13 to 30
  • Adults: 16 to 30
• 1-methylhistidine
  • Children: not measured
  • Adults: not measured
• 3-methylhistidine
  • Children: 0 to 52
  • Adults: 0 to 64
• Ornithine
  • Children: 44 to 90
  • Adults: 27 to 80
• Phenylalanine
  • Children: 26 to 86
  • Adults: 41 to 68
• Phosphoserine
  • Children: 0 to 12
  • Adults: 0 to 12
• Phosphoethanolamine
  • Children: 0 to 12
  • Adults: 0 to 55
• Proline
  • Children: 130 to 290
  • Adults: 110 to 360
• Serine
  • Children: 93 to 150
  • Adults: 56 to 140
• Taurine
  • Children: 11 to 120
  • Adults: 45 to 130
• Threonine
  • Children: 67 to 150
  • Adults: 92 to 240
• Tyrosine
  • Children: 26 to 110
  • Adults: 45 to 74
• Valine
  • Children: 160 to 350
  • Adults: 150 to 310

An increase in the total level of amino acids in the blood amino may be due to:

• Eclampsia
• Fructose intolerance
• Ketoacidosis (from diabetes)
• Kidney failure
• Reye syndrome

A decrease in the total level of amino acids in the blood may be due to:

• Adrenal cortical hyperfunction
• Fever
• Hartnup disease
• Huntington's chorea
• Malnutrition
• Nephrotic syndrome
• Phlebotomus fever
• Rheumatoid arthritis

High or low concentrations of individual plasma amino acids must be interpreted along with other clinical information. Abnormal results may be due to diet, hereditary problems with the ability of the body to handle the amino acid, or to drug effects.

Risks associated with having blood drawn are slight:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Screening infants for increased levels of amino acids can lead to early diagnosis of inborn errors of metabolism. Early treatment for such conditions may prevent complications such as severe mental retardation.