Plasma amino acids

Definition

Plasma amino acids is a screening test, usually 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.

Alternative Names

Amino acids blood test

How the Test is Performed

Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin.

  • The blood collects in a small glass tube called a pipette, or onto a slide or test strip.
  • A bandage is put over the spot to stop any bleeding.

The blood sample is sent to a lab. There are several types of methods used to determine the individual amino acid levels in the blood.

How to Prepare for the Test

The person having the test may be asked not to eat 3 or more hours before the test. Check with your child's health care provider for specific advice.

How the Test will Feel

There might be slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn. The needle stick will probably cause an infant or child to cry.

Why the Test is Performed

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

An increased level of a particular amino acid shows 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.

Increased or decreased levels of amino acids in the blood may occur with fevers, inadequate nutrition, and certain medical conditions.

Normal Results

All measurements are in micromoles per liter (µmol/L). In children, normal values vary with age. In addition, normal values may vary between different laboratories. Talk to your provider about your specific test results.

Alanine:

  • Children: 156 to 598
  • Adults: 125 to 564

Alpha-aminoadipic acid:

  • Children: 0 to 2
  • Adults: 0 to 2

Alpha-amino-N-butyric acid:

  • Children: 6 to 34
  • Adults: 5 to 34

Arginine:

  • Children: 33 to 122
  • Adults: 32 to 150

Asparagine:

  • Children: 32 to 101
  • Adults: 30 to 85

Aspartic acid:

  • Children: 1 to 8
  • Adults: 1 to 7

Beta-alanine:

  • Children: 1 to 8
  • Adults: 1 to 9

Beta-amino-isobutyric acid:

  • Children: 0 to 3
  • Adults: 0 to 4

Carnosine:

  • Children: not detected
  • Adults: not detected

Citrulline:

  • Children: 12 to 47
  • Adults: 14 to 63

Cystine:

  • Children: 9 to 36
  • Adults: 14 to 60

Glutamic acid:

  • Children: 18 to 142
  • Adults: 18 to 156

Glutamine:

  • Children: 330 to 726
  • Adults: 332 to 754

Glycine:

  • Children: 129 to 430
  • Adults: 132 to 467

Histidine:

  • Children: 50 to 104
  • Adults: 47 to 99

Hydroxyproline:

  • Children: 9 to 45
  • Adults: 5 to 35

Isoleucine:

  • Children: 28 to 110
  • Adults: 28 to 113 

Leucine:

  • Children: 57 to 194
  • Adults: 55 to 205

Lysine:

  • Children: 83 to 240
  • Adults: 94 to 278

Methionine:

  • Children: 13 to 40
  • Adults: 13 to 41

1-methylhistidine:

  • Children: not detected
  • Adults: not detected

3-methylhistidine:

  • Children: 0 to 52
  • Adults: 0 to 64

Ornithine:

  • Children: 27 to 136
  • Adults: 31 to 131 

Phenylalanine:

  • Children: 32 to 103
  • Adults: 34 to 102

Phosphoserine:

  • Children: 0 to 12
  • Adults: 0 to 12

Phosphoethanolamine:

  • Children: 0 to 12
  • Adults: 0 to 55

Proline:

  • Children: 85 to 365
  • Adults: 85 to 353

Serine:

  • Children: 60 to 172
  • Adults: 49 to 145 

Taurine:

  • Children: 33 to 126
  • Adults: 29 to 132

Threonine:

  • Children: 56 to 193
  • Adults: 68 to 212

Tyrosine:

  • Children: 32 to 123
  • Adults: 31 to 118

Valine:

  • Children: 110 to 334
  • Adults: 103 to 345

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

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

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

High or low amounts of individual plasma amino acids must be considered with other information. Abnormal results may be due to diet, hereditary problems, or effects of a medicine.

Considerations

Screening infants for increased levels of amino acids can help detect problems with metabolism. Early treatment for these conditions may prevent complications in the future.

References

Dietzen DJ, Vieira Willrich MA. Amino acids, peptides, and proteins. In: Rifai N, Chiu RWK, Young I, Burnham C-A D, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. St Louis, MO: Elsevier; 2023:chap 31.

Kliegman RM, St. Geme JW, Blum NJ, et al. Defects in metabolism of amino acids. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 105.

McPherson RA. Specific proteins. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 20.

Merritt JL, Gallagher RC. Inborn errors of carbohydrate, ammonia, amino acid, and organic acid metabolism. In: Gleason CA, Sawyer T, eds. Avery's Diseases of the Newborn. 11th ed. Philadelphia, PA: Elsevier; 2024:chap 29.

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Review Date: 4/8/2025
Reviewed By: Anna C. Edens Hurst, MD, MS, Associate Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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