Allo-isoleucine, Blood Spot
Use
This test is useful for the evaluation of newborn screening specimens that test positive for branched-chain amino acids elevations. It is also significant for the follow-up of patients diagnosed with maple syrup urine disease (MSUD), which is caused by a deficiency of the branched-chain-ketoacid dehydrogenase complex. Abnormal concentrations of allo-isoleucine are considered pathognomonic for MSUD, helping to differentiate it from BCAA elevations due to dietary influences, thereby reducing false-positive results in newborn screening.
Special Instructions
Not provided.
Limitations
This test has no significant cautionary statements. It is important to note that allo-isoleucine is nearly undetectable in individuals not affected by MSUD, thus its presence is diagnostic. False positives in screening can occur if samples are affected by dietary interference, thus careful clinical consideration is advised. Proper specimen collection and condition are crucial for accurate results.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
LOINC Codes
- 94571-7 - Branched chain aa Pnl DBS
- 94572-5 - Alloisoleucine DBS-sCnc
- 47679-6 - Leucine DBS-sCnc
- 47671-3 - Isoleucine DBS-sCnc
- 47799-2 - Valine DBS-sCnc
- 46743-1 - MSUD DBS-Imp
- 18771-6 - Provider signing name
Result Turnaround Time
2-4 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
2 Blood spots
Minimum Volume
1 Blood spot
Container
Blood Spot Collection (Filter Paper)
Collection Instructions
Do not use a device or capillary tube containing EDTA to collect the specimen. At least 1 spot should be complete and unpunched. Alternative collection for patients older than 1 year is a fingerstick. Allow the blood to dry completely on the filter paper at ambient temperature in a horizontal position for a minimum of 3 hours.
Storage Instructions
Keep specimen dry. Do not stack wet specimens.
Causes for Rejection
Blood spot specimen that shows layering, serum rings, multiple applications, or insufficient specimen.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 59 days |
| Refrigerated | 59 days |
| Frozen | 59 days |