Amino Acid Screen, Blood

Amino Acid Screen, Blood

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

Plasma (1 mL) collected in a green-top (heparin) tube.

Normal findings

(Method: Liquid chromatography/mass spectrometry) 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 PKU, tyrosinuria, and alcaptonuria, a defect in the phenylalanine-tyrosine conversion pathway. Accumulation of phenylalanine, in infants lacking the enzyme phenylalanine hydroxylase, results in progressive mental retardation. 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 quantitation from plasma specimens is 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. 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.
  • Detect 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, with liver disease, or when there is impaired clearance by the kidneys:

  • Aminoacidopathies (usually related to an inherited disorder; specific amino acids are implicated)
  • Burns (related to increased protein turnover)
  • Diabetes (related to gluconeogenesis, where protein is broken down as a means to generate glucose)
  • Fructose intolerance (related to hereditary enzyme deficiency)
  • Malabsorption (related to lack of transport and opportunity for catabolism)
  • Renal failure (acute or chronic) (related to impaired clearance)
  • Reyes syndrome (related to liver damage)
  • Severe liver damage (related to decreased production of amino acids by the liver)
  • Shock (related to increased protein turnover from tissue death and decreased deamination due to impaired liver function)

Decreased in

    Decreased (total amino acids) in conditions that result in increased renal excretion or insufficient protein intake or synthesis:

    Adrenocortical hyperfunction (related to excess cortisol, which assists in conversion of amino acids into glucose) Carcinoid syndrome (related to increased consumption of amino acids, especially tryptophan, to form serotonin) Fever (related to increased consumption) Glomerulonephritis (related to increased renal excretion) Hartnup’s disease (related to increased renal excretion) Huntington’s chorea (related to increased consumption due to muscle tremors; possible insufficient intake) Malnutrition (related to insufficient intake) Nephrotic syndrome (related to increased renal excretion) Pancreatitis (acute) (related to increased consumption as part of the inflammatory process and increased ureagenesis) Polycystic kidney disease (related to increased renal excretion) Rheumatoid arthritis (related to insufficient intake evidenced by lack of appetite)

Critical findings

    N/A

Interfering factors

  • Drugs that may increase plasma amino acid levels include amino acids, bismuth salts, glucocorticoids, levarterenol, and 11-oxysteroids.
  • Drugs that may decrease plasma amino acid levels include diethylstilbestrol, epinephrine, insulin, and progesterone.
  • 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.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.
  • Specimens for newborn screening that are collected after transfusion may produce invalid results.
  • Specimens for newborn screening that are collected earlier than 24 hr after the first feeding or from neonates receiving total parenteral nutrition may produce invalid results.
  • Specimens for newborn screening that are improperly applied to the filter paper circles may produce invalid results.
  • Touching blood spots after collection on the filter paper card may contaminate the sample and produce invalid results.

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/caregiver this test can assist in identification of inborn infant disorders. Education regarding newborn screening should begin during the prenatal period and be reinforced at the time of preadmission testing. Many birthing facilities and hospitals provide educational brochures to the parents. Physicians and physician delegates are responsible for informing parents of the newborn screening process before discharge.
  • 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/or caregiver) that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture. Explain, as appropriate, that specimens from neonates are collected by heel stick and applied to filter paper spots on the birth state’s specific screening program card.
  • 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 as protein intake may alter results. If the patient is a neonate, most state regulations require screening specimens to be collected between 24 and 48 hr after birth, to allow sufficient time after protein intake for abnormal metabolites to be detected, and preferably before blood product transfusion or physical transfer to another facility.
  • Note that there are no fluid or medication restrictions unless by medical direction.

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.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient (and/or caregiver) to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement. The caregiver may assist in preventing unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container/card with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture or heel stick. When collecting samples for newborn screening, it is important to apply each blood drop to the correct side of the filter paper card and fill each circle with a single application of blood. Overfilling or underfilling the circles will cause the specimen card to be rejected by the testing facility. Additional information is required on newborn screening cards and may vary by state.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture or heel stick site for bleeding or hematoma formation, and secure gauze with adhesive bandage. Newborn screening cards should be allowed to air dry for several hours on a level, nonabsorbent, unenclosed area. If multiple patients are tested, do not stack cards. State regulations usually require the specimen cards to be submitted within 24 hr of collection.
  • Promptly transport the specimen to the laboratory for processing and analysis.

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 the state department of health 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, newborn screening, and urine amino acid screen.
  • See the Genitourinary, Hepatobiliary, and Reproductive systems tables at the end of the book for related tests by body system.