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HelpTest ID ALLOI Allo-isoleucine, Blood Spot
Reporting Name
Allo-isoleucine, BSUseful For
Evaluation of newborn screening specimens that test positive for branched-chain amino acids elevations
Follow-up of patients with maple-syrup urine disease
Specimen Type
Whole bloodSpecimen Required
Supplies: Card - Blood Spot Collection (Filter Paper) (T493)
Container/Tube: Local newborn screening card
Specimen Volume: 2 Blood spots
Collection Instructions:
1. Do not use device or capillary tube containing EDTA to collect specimen.
2. At least 1 spot should be complete and unpunched.
3. An alternative blood collection option for a patient >1 year of age is fingerstick.
4. Include type of feeding information on the collection card.
5. Do not expose specimen to heat or direct sunlight.
6. Do not stack wet specimens.
7. Keep specimen dry.
8. Let blood dry on the Blood Spot Collection Card (T493) at ambient temperature in a horizontal position for 3 hours before adding additional blood spots to the card.
Additional Information:
1. For collection instructions, see Blood Spot Collection Instructions in Special Instructions.
2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777) in Special Instructions.
3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800) in Special Instructions.
Specimen Minimum Volume
1 Blood spot
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole blood | Ambient (preferred) | FILTER PAPER | |
| Frozen | FILTER PAPER | ||
| Refrigerated | FILTER PAPER | ||
Reference Values
Allo-isoleucine: <2 nmol/mL
Leucine: 35-215 nmol/mL
Isoleucine: 13-130 nmol/mL
Valine: 51-325 nmol/mL
An interpretive report will also be provided.
Day(s) and Time(s) Performed
Monday through Friday; Varies
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.CPT Code Information
82136
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| ALLOI | Allo-isoleucine, BS | 94571-7 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 27446 | Specimen | 31208-2 |
| 27447 | Specimen ID | 57723-9 |
| 27448 | Source | 31208-2 |
| 27449 | Order Date | 82785-7 |
| 27450 | Reason For Referral | 42349-1 |
| 27451 | Method | 85069-3 |
| 27457 | Allo-isoleucine | 94572-5 |
| 27458 | Leucine | 47679-6 |
| 27459 | Isoleucine | 47671-3 |
| 27460 | Valine | 47799-2 |
| 27453 | Interpretation | 46743-1 |
| 27454 | Amendment | 48767-8 |
| 27455 | Reviewed By | 18771-6 |
| 27456 | Release Date | 82772-5 |
Clinical Information
Maple-syrup urine disease (MSUD) is an inborn error of metabolism caused by the deficiency of the branched-chain-ketoacid dehydrogenase (BCKDH) complex. The BCKDH complex is involved in the metabolism of the branched-chain amino acids (BCAA): isoleucine (Ile), leucine (Leu), and valine (Val). Classic MSUD presents in the neonate with feeding intolerance, failure to thrive, vomiting, lethargy, and maple-syrup odor to urine and cerumen. If untreated, it progresses to irreversible mental retardation, hyperactivity, failure to thrive, seizures, coma, cerebral edema, and possibly death.
MSUD is a pan-ethnic condition but is most prevalent in the Old Order Mennonite community in Lancaster, Pennsylvania with an incidence there of 1:760 live births. The incidence of MSUD is approximately 1:200,000 live births in the general population.
Newborn screening includes the measurement of BCAA (Leu, Ile, and Val), which are elevated in MSUD. However, unaffected infants receiving total parenteral nutrition frequently have increased levels of BCAA, a situation that often triggers unnecessary follow-up investigations. Abnormal concentrations of allo-isoleucine (Allo-Ile) are pathognomonic for MSUD. The determination of Allo-Ile (second-tier testing) in the same newborn screening specimens that reveals elevated BCAA allows for positive identification of patients with MSUD and differentiation from BCAA elevations due to dietary artifacts, reducing the occurrence of false-positive newborn screening results.
Treatment of MSUD aims to normalize the concentration of BCAA by dietary restriction of these amino acids. BCAA are essential amino acids, which require frequent adjustment of the dietary treatment. Dietary monitoring is accomplished by regular determination of BCAA and Allo-Ile concentrations.
Interpretation
Allo-isoleucine is nearly undetectable in individuals not affected by maple-syrup urine disease (MSUD). Accordingly, its presence is diagnostic for MSUD, and its absence is sufficient to rule-out MSUD.
Clinical Reference
1. Chace DH, Kalas TA, Naylor EW: Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns. Clin Chem. 2003;49(11):1797-1817
2. Simon E, Fingerhut R, Baumkotter J, Konstantopoulou V, Ratschmann R, Wendel U: Maple syrup urine disease: Favorable effect of early diagnosis by newborn screening on the neonatal course of the disease. J Inherit Metab Dis. 2006;29:532-537
3. Morton DH, Strauss KA, Robinson DL, Puffenberger EG, Kelley RI: Diagnosis and treatment of maple syrup disease: a study of 36 patients. Pediatrics. 2002;109:999-1008
4. Strauss KA, Puffenberger EG, Carson VJ: Maple syrup urine disease. In: Adam MP, Ardinger HH, Pagon RA, et al. eds. GeneReviews [Internet]. University of Washington, Seattle; 2006. Updated April 23, 2020. Accessed December 16, 2020. Available at www.ncbi.nlm.nih.gov/books/NBK1319/
Analytic Time
2 daysMethod Name
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Portions of this test are covered by patents held by Quest Diagnostics
Special Instructions
Forms
If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.
mcl-newborn