Test ID: ALLOI
Allo-isoleucine, Blood Spot
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Evaluation of newborn screening samples that test positive for branched-chain amino acids elevations
Follow-up of patients with maple-syrup urine disease
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
Second-tier test for abnormal newborn screen and follow-up of patients with maple syrup urine disease (MSUD).
Method Name A short description of the method used to perform the test
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) Stable Isotope Dilution Analysis
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Branched-Chain Amino Acids (BCAA) Elevations
Newborn Screen
Newborn Screening
Maple Syrup Urine Disease (MSUD)
Maple Syrup Disease (MSD)
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
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, unpunched.
3. An alternative blood collection option for a patient >1 year of age is fingerstick. Include type of feeding information on the collection card.
4. Do not expose specimen to heat or direct sunlight.
5. Do not stack wet specimens.
6. Keep specimen dry.
7. If collection of a new specimen is necessary, let blood dry on the Supplemental Newborn Screening Card (Supply T493) at ambient temperature in a horizontal position for 3 hours.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole blood | Ambient (preferred) | |
| Frozen | ||
| Refrigerated | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Maple-syrup urine disease (MSUD) is an autosomal recessive 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 panethnic condition, but is most prevalent in the Old Order Mennonite community in Lancaster, Pennsylvania. The incidence of MSUD is approximately 1:200,000 live births in the general population and 1:760 live births among the Old Order Mennonites.
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 artefacts, 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. Because BCAA belong to the essential amino acids, the dietary treatment requires frequent adjustment, which is accomplished by regular determination of BCAA and Allo-Ile concentrations.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
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.
Interpretation Provides information to assist in interpretation of the test results
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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements.
Supportive Data
In a blinded study containing specimens obtained from maple-syrup urine disease (MSUD) cases (n=16), non-MSUD patients treated with total parenteral nutrition (n=19), and healthy controls (n=541), this assay correctly identified all MSUD and non-MSUD cases.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Chace DH, Hillman SL, Millington DS, et al: Rapid diagnosis of maple syrup urine disease in blood spots from newborns by tandem mass spectrometry. Clin Chem 1995;41:62-68
2. Simon E, Fingerhut R, Baumkotter J, et al: 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, et al: Diagnosis and treatment of maple syrup disease: a study of 36 patients. Pediatrics 2002;109:999-1008
Method Description Describes how the test is performed and provides a method-specific reference
This method quantifies valine (Val), allo-isoleucine (Allo-Ile), leucine (Ile), and leucine (Leu) using stable isotope-labeled internal standards (IS): d8-Val, d10-Allo-Ile, and d3-Leu. Branched-chain amino acids (BCAA) are extracted from a 3/16-inch dried blood spot (DBS) using a methanol:H2O (50:50) solution containing the IS. The filter plate containing the DBS and the IS is placed on an orbital shaker for 30 minutes at ambient temperature. The blood spot eluate is centrifuged into a 96-well round-bottom plate, dried under nitrogen, and reconstituted in aqueous mobile phase. BCAA are separated and detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) (SCIEX API 3200) in positive selected reaction monitoring mode. Chromatography is performed using an Applied Biosystems AAA C18 (4.6 x 150 mm) column, with mobile phases 0.1% formic acid:0.01% heptofluorobutyric acid (HFBA):H20 and 0.1% formic acid:0.01% HFBA:acetonitrile. Total analysis time is 15 minutes including column re-equilibration. (Oglesbee D, Kramer K, Lacey J, et al: Quantitative determination of allo-isoleucine and other branched chain amino acids in dried blood spots for newborn screening of maple-syrup urine disease [MSUD], unpublished Mayo method)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Friday; afternoon
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
82136
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 27446 | Specimen | 31208-2 |
| 27447 | Specimen ID | N/A |
| 27448 | Source | N/A |
| 27449 | Order Date | N/A |
| 27450 | Reason For Referral | 42349-1 |
| 27451 | Method | 49549-9 |
| 27457 | Allo-isoleucine | 22670-4 |
| 27458 | Leucine | 20649-0 |
| 27459 | Isoleucine | 20648-2 |
| 27460 | Valine | 20661-5 |
| 27453 | Interpretation | 59462-2 |
| 27454 | Amendment | In Process |
| 27455 | Reviewed By | In Process |
| 27456 | Release Date | N/A |
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