Amino Acid Screen, Urine

Amino Acid Screen, Urine

Synonym/acronym: N/A.

Common use

To assist in diagnosing congenital metabolic disorders in infants, typically homocystinuria, maple syrup urine disease, phenylketonuria (PKU), tyrosinuria, and unexplained mental retardation.

Specimen

Urine (10 mL) from a random or timed specimen collected in a clean plastic collection container with hydrochloric acid as a preservative.

Normal findings

(Method: Chromatography) There are numerous amino acids. Values vary, and the testing laboratory should be consulted for corresponding ranges.

Description

Amino acids are required for the production of proteins, enzymes, coenzymes, hormones, nucleic acids used to form DNA, pigments such as hemoglobin, and neurotransmitters. Testing for specific aminoacidopathies is generally performed on infants after an initial screening test with abnormal results. All 50 states have neonatal screening programs. Tests included in the screening profile vary among states. Certain congenital enzyme deficiencies interfere with normal amino acid metabolism and cause excessive accumulation of or deficiencies in amino acid levels. The major genetic disorders include phenylketonuria (PKU), tyrosinuria, and alcaptonuria, a defect in the phenylalanine-tyrosine conversion pathway. Renal aminoaciduria is also associated with conditions marked by defective tubular reabsorption from congenital disorders, such as hereditary fructose intolerance, cystinuria, and Hartnup’s disease. Early diagnosis and treatment of certain aminoacidopathies can prevent mental retardation, reduced growth rates, and various unexplained symptoms. In most cases when plasma levels are elevated, urine levels are also elevated. Amino acid quantitations from plasma specimens are more informative, less variable, and less prone to analytic interference than from urine specimens. Urine specimens may be required to assist in the identification of disorders involving defective renal transport, where elevated levels are only manifested in the urine. Values are age dependent. Abnormal results on a random sample should be followed up with a timed collection. Amino acid concentrations demonstrate a significant circadian rhythm with values being lowest in the morning and highest in midafternoon.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the detection of noninherited disorders evidenced by elevated amino acid levels
  • Screen for congenital errors of amino acid metabolism

Potential diagnosis

Increased in

  • Increased amino acid accumulation (total amino acids) occurs when a specific enzyme deficiency prevents its catabolism or when there is impaired clearance by the kidneys:

  • Primary causes (inherited):
    • Aminoaciduria (specific)
    • Cystinosis(may be masked because of decreased glomerular filtration rate, so values may be in normal range)
    • Fanconi’s syndrome
    • Fructose intolerance
    • Galactosemia
    • Hartnup’s disease
    • Lactose intolerance
    • Lowe’s syndrome
    • Maple syrup urine disease
    • Tyrosinemia type I
    • Tyrosinosis
    • Wilson’s disease
  • Secondary causes (noninherited):
    • Acute leukemia
    • Chronic renal failure (reduced glomerular filtration rate)
    • Chronic renal failure
    • Diabetic ketosis
    • Epilepsy (transient increase related to disturbed renal function during grand mal seizure)
    • Folic acid deficiency
    • Hyperparathyroidism
    • Liver necrosis and cirrhosis
    • Multiple myeloma
    • Muscular dystrophy (progressive)
    • Osteomalacia (secondary to parathyroid hormone excess)
    • Pernicious anemia
    • Thalassemia major
    • Vitamin deficiency (B, C, and D; vitamin D–deficiency rickets, vitamin D–resistant rickets)
    • Viral hepatitis (related to the degree of hepatic involvement)

Decreased in

    N/A

Critical findings

    N/A

Interfering factors

  • Drugs that may increase urine amino acid levels include acetylsalicylic acid, bismuth, cisplatin, corticotropin, hydrocortisone, insulin, streptozocin, tetracycline, triamcinolone, and valproic acid.
  • Numerous drugs may affect the test method and falsely increase urine amino acid levels.
  • Drugs that may decrease urine amino acid levels include insulin.
  • Amino acids exhibit a strong circadian rhythm; values are highest in the afternoon and lowest in the morning. Protein intake does not influence diurnal variation but significantly affects absolute concentrations.
  • Dilute urine (specific gravity less than 1.010) should be rejected for analysis.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:  Inform the parent this test can assist in identification of inborn infant disorders.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s genitourinary and hepatobiliary systems, the patient’s and parents’ reproductive system as it relates to genetic disease, the patient’s symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient (and/or caregiver). Inform the patient and caregiver that random urine specimen collection takes approximately 5 min. Address concerns about pain and explain that no pain will be experienced during the test.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to fast for 12 hr prior to the procedure.
  • Note that there are no fluid or medication restrictions unless by medical direction.
  • Instruct the patient to avoid excessive exercise and stress during the 24-hr collection of urine.
  • Review the procedure with the patient (and/or caregiver). Provide a nonmetallic urinal, bedpan, or toilet-mounted collection device.
  • Inform the patient that all urine collected over a 24-hr period must be saved if a timed collection is requested; if a preservative has been added to the container, instruct the patient not to discard the preservative. Instruct the patient not to void directly into the laboratory collection container. Instruct the patient to avoid defecating in the collection device and to keep toilet tissue out of the collection device to prevent contamination of the specimen. Place a sign in the bathroom to remind the patient to save all urine.
  • Instruct the patient to void all urine into the collection device and pour the urine into the laboratory collection container. Alternatively, the specimen can be left in the collection device for a health care staff member to add to the laboratory collection container.

Intratest

  • Potential complications: N/A
  • Ensure that the patient has complied with dietary and other pretesting preparations; assure that food has been restricted for at least 12 hr prior to the procedure as protein intake may alter results.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Include on the timed specimen label the amount of urine and test start and stop times.
  • Promptly transport the specimen to the laboratory for processing and analysis.

    • Random Specimen (collect in early morning)

  • Infant: Clean and dry the genital area, attach the collection device securely to prevent leakage, and observe for voiding. Remove collection device carefully from the skin to prevent irritation. Transfer the urine into a specimen container. For dipstick method, place dipstick or reagent pad into the urine specimen or on the diaper saturated with urine. Remove, compare with color chart, and record results.
  • Adult: Instruct the patient to obtain a clean-catch specimen as described in Patient Preparation and Specimen Collection. If an indwelling catheter is in place, it may be necessary to clamp off the catheter for 15 to 30 min before specimen collection. Cleanse specimen port with antiseptic swab, and then aspirate 5 mL of urine with a 21- to 25-gauge needle and syringe. Transfer urine to a properly labeled plastic container.

    • Timed Specimen

  • Obtain a clean 3-L urine specimen container, toilet-mounted collection device, and plastic bag (for transport of the specimen container). The specimen must be refrigerated or kept on ice throughout the entire collection period. If an indwelling urinary catheter is in place, the drainage bag must be kept on ice.
  • Begin the test between 6 and 8 a.m. if possible. Collect first voiding and discard. Record the time the specimen was discarded as the beginning of the timed collection period. The next morning, ask the patient to void at the same time the collection was started, and add this last voiding to the container. Urinary output should be recorded throughout the collection time.
  • If an indwelling catheter is in place, replace the tubing and container system at the start of the collection time. Keep the container system on ice during the collection period, or empty the urine into a larger container periodically during the collection period; monitor to ensure continued drainage, and conclude the test the next morning at the same hour the collection started.
  • Compare the quantity of urine with the urinary output record for the collection at the conclusion of the test. If the specimen contains less than what was recorded as output, some urine may have been discarded, invalidating the test.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Instruct the patient to resume usual diet as directed by the HCP.
  • Nutritional Considerations: Instruct the patient (and/or caregiver) in special dietary modifications, as appropriate to treat deficiency, or refer caregiver to a qualified nutritionist. Amino acids are classified as essential (i.e., must be present simultaneously in sufficient quantities); conditionally or acquired essential (i.e., under certain stressful conditions, they become essential); and nonessential (i.e., can be produced by the body, when needed, if diet does not provide them). Essential amino acids include lysine, threonine, histidine, isoleucine, methionine, phenylalanine, tryptophan, and valine. Conditionally essential amino acids include cysteine, tyrosine, arginine, citrulline, taurine, and carnitine. Nonessential amino acids include alanine, glutamic acid, aspartic acid, glycine, serine, proline, glutamine, and asparagine. A high intake of specific amino acids can cause other amino acids to become essential.
  • Recognize anxiety related to test results, and be supportive of perceived loss of independence and fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient (and/or caregiver) regarding access to genetic or other counseling services. Provide contact information, if desired, for the March of Dimes (www.marchofdimes.com) or your state department of health’s newborn screening program.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ammonia, amino acid screen blood, and newborn screening.
  • See the Genitourinary, Hepatobiliary, and Reproductive systems tables at the end of the book for related tests by body system.