Amino Acids Full Panel
Free amino acids can be measured in plasma, urine, or cerebrospinal fluid (CSF), depending on the clinical concern. Plasma amino acids are indicated when following up infants with positive newborn screening result, evaluating patients with symptoms and signs of a possible metabolic condition (such as lethargy, vomiting, and failure to thrive), and monitoring individuals with a metabolic condition. This assay is sensitive in detecting specific amino acid disorders including phenylketonuria, maple syrup urine disease, tyrosinemias, urea cycle disorders, homocytinuria and various organic acidemias, etc.
For diagnostic purposes, it is best to combine amino acid findings with other metabolic profiles such as plasma acylcarnitine/carnitine and urine organic acids analysis to achieve an accurate diagnosis. Because plasma amino acid levels can be impacted by a patient’s nutritional and clinical status, a fasting or a pre-feed sample (infants) is required. Additionally, sample condition (hemolysis, etc) may also alter certain amino acid concentrations. Therefore, plasma should be immediately separated from whole blood and kept frozen until submission.
Urine amino acids are used to identify generalized or specific disorders of renal amino acid transport (eg, renal Fanconi syndrome, cystinuria).
CSF amino acids are evaluated to identify disorders of amino acid metabolism that affect the central nervous system (eg, glycine encephalopathy and serine biosynthesis disorders). Concurrent plasma amino acids analysis is required when testing CSF amino acids for these conditions.
Liquid chromatography and tandem mass spectrometry (LC-MS/MS) method or ion exchange chromatography method is used for the measurement of amino acid concentrations.
- Plasma: 2-3 mL of blood in sodium heparin tube (green top), fasting or 4 hours postprandial. Infants should be drawn just before next feeding. Avoid drawing while on TPN. Centrifuge immediately and freeze plasma. A minimum of 0.5 mL blood (0.2 mL plasma) is required
- Urine: 5 mL (random or preferably morning first void) in a clean container without preservatives; freeze
- CSF: Collect 1 mL spinal fluid in a sterile container without additives; freeze. (Note: blood contamination can interfere with test results)
- Ship overnight frozen on dry ice
- Routine: 3-5 days
- Emergency: Same day results available on an emergency basis. Please call the laboratory prior to sending a sample for STAT analysis