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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.

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 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). Normal values may vary between different laboratories. Talk to your health care provider about your specific test results.

Alanine:

Alpha-aminoadipic acid:

Alpha-amino-N-butyric acid:

Arginine:

Asparagine:

Aspartic acid:

Beta-alanine:

Beta-amino-isobutyric acid:

Carnosine:

Citrulline:

Cystine:

Glutamic acid:

Glutamine:

Glycine:

Histidine:

Hydroxyproline:

Isoleucine:

Leucine:

Lysine:

Methionine:

1-methylhistidine:

3-methylhistidine:

Ornithine:

Phenylalanine:

Phosphoserine:

Phosphoethanolamine:

Proline:

Serine:

Taurine:

Threonine:

Tyrosine:

Valine:

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, Shah SS, Tasker RC, Wilson KM. Defects in metabolism of amino acids. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 103.

Riley RS, McPherson RA. Basic examination of urine. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2022:chap 29.

Schedule An Appointment

Contact Atlanta Obsetrics and Gynaecology at The Womens Center Millennium Hospital - 404-ATL-BABY

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Review Date: 4/24/2023

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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