Alternative names
Amino acids - urine; Aminoaciduria

Definition
This test screens for increased levels of amino acid excretion in the urine that indicates possible inborn errors of metabolism caused by a specific enzyme deficiency.

How the test is performed

To obtain a clean-catch urine sample, males should wipe clean the head of the penis and females need to wipe between the labia with soapy water and rinse well. Sometimes a special clean-catch kit is provided with cleansing solution and sterile wipes.

After urinating a small amount into the toilet bowl to clear the urethra of contaminants, collect a sample of urine in a clean or sterile container. About 1 to 2 ounces of urine is needed for a test. Remove the container from the urine stream without stopping the flow. You may finish voiding into the toilet bowl. Take the sample to the lab.

For infants:
Your infant’s genital area will be cleaned and dried, then a collection device is attached to collect the urine. If you are asked to collect the urine, be sure the collection device is attached securely to prevent leakage. After your baby has urinated, the urine (at least 20 cc) is transferred to a sterile container.

How to prepare for the test
No restriction of food or fluid is necessary.

Inform your health care provider of any medication you or your child has used recently. If your infant is breast feeding and having this test performed, inform the health care provider of any medications the mother is taking.

How the test will feel
The test involves only normal urination.

Why the test is performed

This test is performed to assess amino acid levels in the urine. It is common for some of each amino acid to be in the urine, but elevated levels of individual amino acids indicates a possible inborn enzyme deficiency.

While this test shows increased levels of amino acids in the urine, a 24-hour quantitative urine chromatography is necessary to accurately measure the elevated levels of the specific amino acids.

The increased levels also show up in the blood plasma (see plasma amino acids). If the test is performed early enough on infants and the defect is treated, the severe mental retardation that can result may be prevented.

Normal Values

 
• alanine       o children: 65 to 190       o adults: 160 to 690  
• alpha-aminoadipic acid       o children: 25 to 78       o adults: 0 to 165  
• alpha-amino-N-butyric acid       o children: 7 to 25       o adults: 0 to 28  
• arginine       o children: 10 to 25       o adults: 13 to 64  
• asparagine       o children: 15 to 40       o adults: 34 to 100  
• aspartic acid       o children: 10 to 26       o adults: 14 to 89  
• beta-alanine       o children: 0 to 42       o adults: 0 to 93  
• beta-amino-isobutyric acid       o children: 25 to 96       o adults: 10 to 235  
• carnosine       o children: 34 to 220       o adults: 16 to 125  
• citrulline       o children: 0 to 13       o adults: 0 to 11  
• cystine       o children: 11 to 53       o adults: 28 to 115  
• glutamic acid       o children: 13 to 22       o adults: 27 to 105  
• glutamine       o children: 150 to 400       o adults: 300 to 1,040  
• glycine       o children: 195 to 855       o adults: 750 to 2,400  
• histidine       o children: 46 to 725       o adults: 500 to 1,500  
• hydroxyproline       o children: not measured       o adults: not measured  
• isoleucine       o children: 3 to 15       o adults: 4 to 23  
• leucine       o children: 9 to 23       o adults: 20 to 77  
• lysine       o children: 19 to 140       o adults: 32 to 290  
• methionine       o children: 7 to 20       o adults: 5 to 30  
• 1-methylhistidine       o children: 41 to 300       o adults: 68 to 855  
• 3-methylhistidine       o children: 42 to 135       o adults: 64 to 320  
• ornithine       o children: 3 to 16       o adults: 5 to 70  
• phenylalanine       o children: 20 to 61       o adults: 36 to 90  
• phosphoserine       o children: 16 to 34       o adults: 28 to 95  
• phosphoethanolamine       o children: 24 to 66       o adults: 17 to 95  
• proline       o children: not measured       o adults: not measured  
• serine       o children: 93 to 210       o adults: 200 to 695  
• taurine       o children: 62 to 970       o adults: 267 to 1,290  
• threonine       o children: 25 to 100       o adults: 80 to 320  
• tyrosine       o children: 30 to 83       o adults: 38 to 145  
• valine       o children: 17 to 37       o adults: 19 to 74

Comparison is necessary with the plasma amino acids to develop a complete picture of the aminoacidurias.

Note: all measurements in micro mole per deciliter (micro mol/dl)

What abnormal results mean
Increased total urine amino acids may indicate any of the following:

 
• alkaptonuria  
• Canavan disease  
• cystinosis  
• cystathioninuria  
• fructose intolerance  
• galactosemia  
• Hartnup disease  
• homocystinuria  
• hyperammonemia  
• hyperparathyroidism  
• maple syrup urine disease  
• methylmalonic acidemia  
• multiple myeloma  
• ornithine transcarbamylase deficiency  
• osteomalacia  
• propionic acidemia  
• rickets  
• Tyrosinemia type 1  
• Tyrosinemia type 2  
• viral hepatitis  
• Wilson’s disease

What the risks are
In infants, the collection device should be removed carefully to prevent irritation.

Special considerations
Failure to have the urine sample promptly evaluated in the laboratory alters the results of the test. This test is ineffective in a neonate (the first six weeks after birth) who has not ingested dietary protein in the last 48 hours.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.