Plasma amino acids

Alternative names
Amino acids - plasma

Definition
This is a screening test performed on infants that detects problems with amino acid metabolism.

How the test is performed
The area (usually the heel) is cleansed with antiseptic and the skin is punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Chromatography is then used to analyze the amino acids in your child’s blood.

How to prepare for the test
Fast for 4 hours before the test, or the test results may be altered and invalidated.

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation.

The needle insertion will probably make your infant cry briefly.

Why the test is performed

Amino acids are the building blocks for proteins in the body. Accumulation of amino acids can occur due to abnormalities in the normal mechanisms for their metabolism or elimination. The increased levels show up in plasma (the liquid portion of blood) and urine.

If the test to identify and measure their quantities is performed early enough on an infant with an inherited defect in amino acid metabolism, treatment can often be administered to prevent the severe mental retardation that may otherwise result.

Normal Values

     
  • alanine       o children: 200 to 450       o adults: 230 to 510  
  • alpha-aminoadipic acid       o children: not measured       o adults: not measured  
  • alpha-amino-N-butyric acid       o children: 8 to 37       o adults: 15 to 41  
  • arginine       o children: 44 to 120       o adults: 13 to 64  
  • asparagine       o children: 15 to 40       o adults: 45 to 130  
  • aspartic acid       o children: 0 to 26       o adults: 0 to 6  
  • beta-alanine       o children: 0 to 49       o adults: 0 to 29  
  • beta-amino-isobutyric acid       o children: not measured       o adults: not measured  
  • carnosine       o children: not measured       o adults: not measured  
  • citrulline       o children: 16 to 32       o adults: 16 to 55  
  • cystine       o children: 19 to 47       o adults: 30 to 65  
  • glutamic acid       o children: 32 to 140       o adults: 18 to 98  
  • glutamine       o children: 420 to 730       o adults: 390 to 650  
  • glycine       o children: 110 to 240       o adults: 170 to 330  
  • histidine       o children: 68 to 120       o adults: 26 to 120  
  • hydroxyproline       o children: 0 to 5       o adults: not measured  
  • isoleucine       o children: 37 to 140       o adults: 42 to 100  
  • leucine       o children: 70 to 170       o adults: 66 to 170  
  • lysine       o children: 120 to 290       o adults: 150 to 220  
  • methionine       o children: 13 to 30       o adults: 16 to 30  
  • 1-methylhistidine       o children: not measured       o adults: not measured  
  • 3-methylhistidine       o children: 0 to 52       o adults: 0 to 64  
  • ornithine       o children: 44 to 90       o adults: 27 to 80  
  • phenylalanine       o children: 26 to 86       o adults: 41 to 68  
  • phosphoserine       o children: 0 to 12       o adults: 0 to 12  
  • phosphoethanolamine       o children: 0 to 12       o adults: 0 to 55  
  • proline       o children: 130 to 290       o adults: 110 to 360  
  • serine       o children: 93 to 150       o adults: 56 to 140  
  • taurine       o children: 11 to 120       o adults: 45 to 130  
  • threonine       o children: 67 to 150       o adults: 92 to 240  
  • tyrosine       o children: 26 to 110       o adults: 45 to 74  
  • valine       o children: 160 to 350       o adults: 150 to 310

Note: all measurements in micro mole per liter (micro mol/L); The normal range of values may vary between different laboratories, and the laboratory performing the test should therefore be consulted in interpretation of the test result.

What abnormal results mean

An elevated level of a particular amino acid is highly suggestive of an inherited defect in metabolism of that amino acid. The test for an individual amino acid may also be used for following the effectiveness of a particular treatment.

If the total amino acid level is elevated, several diseases or conditions may be the cause:

     
  • chronic renal failure  
  • acute renal failure  
  • Eclampsia  
  • fructose intolerance  
  • Reye’s syndrome  
  • ketoacidosis (from Diabetes)

If the total amino level is decreased, the following conditions may be responsible:

     
  • fever  
  • malnutrition  
  • Rheumatoid Arthritis  
  • Hartnup disease  
  • Huntington’s chorea  
  • phlebotomus fever  
  • nephrotic syndrome  
  • adrenal cortical hyperfunction

What the risks are

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)

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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