A urine amino acid test measures the level of amino acids in the urine. Approximately 20 different amino acids function as building blocks that combine to form proteins in the body.
A urine amino acid test is ordered when the healthcare professional suspects an inborn error of metabolism. .
Inborn errors of metabolism are genetic conditions in which the person lacks a particular enzyme. Enzymes are substances that allow a person to use protein for various body functions. When an enzyme is missing, the person is unable to use a particular protein appropriately.
The amino acids that make up the protein then build up in the body. Some of them are excreted in the urine. Each disorder can affect the level of one or more amino acids in the urine. A urine amino acid test is generally performed on infants and young children to help diagnose a genetic disorder. It may also be useful for monitoring persons with known amino acid disorders.
To perform this test, a urine sample is needed. A person is asked to supply urine in a special container. Advice on how to get a urine sample from an infant is provided if necessary. The urine sample is taken to a lab for testing.
Generally, no preparation is necessary. The healthcare professional will give instructions if needed.
There are over 20 different amino acids in the urine. A low level of amino acids is normal in the urine. If the level for one or more amino acids is higher than normal, the person may have an inborn error of metabolism. In some cases, early detection in the first year after birth can prevent problems such as brain damage.
The exact level of each of the amino acids in the urine helps diagnose the specific disorder. Further tests, such as blood tests, may be needed to confirm the suspected disorder. Examples of specific disorders that can cause abnormal test results are as follows: cystinuria, which may cause kidney stonesphenylketonuria, or PKU, which can cause mental retardation (this disorder is screened for at birth)
There are many other rare inherited disorders that can cause abnormal test results. Other diseases of the kidney can also cause abnormal test results. Results should be discussed with the healthcare professional.
Taber's Medical Dictionary, Illustrated Guide to Diagnostic Tests