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.
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 should not eat 4 hours before the test.
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 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.
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 micromole per liter (micro mol/L). Normal values may vary between different laboratories. Talk to your health care provider 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
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:
- Eclampsia
- Fructose intolerance
- Ketoacidosis (from diabetes)
- Kidney failure
- Reye syndrome
- Laboratory error
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
- Laboratory error
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 medication.
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.
