Definition of Plasma amino acids:

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

How the test is performed:

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.

How to prepare for the test:

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

See also: Test/procedure preparation - infant

How the test will feel:

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.

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 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.