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HelpOrder Code LAB1562 Hexosaminidase A and Total Hexosaminidase, Serum
Additional Codes
Mayo Test Code: NAGS
Reporting Name
Hexosaminidase A and Total, SUseful For
Carrier detection and diagnosis of Tay-Sachs disease and Sandhoff disease
Ruling out I-cell disease
This test is not useful for pregnant females or those treated with hormonal contraception.
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumOrdering Guidance
Testing for Tay-Sachs Disease and Sandhoff Disease
The following tests are available for diagnostic and carrier testing for Tay-Sachs and Sandhoff diseases.
NAGR / Hexosaminidase A and Total, Leukocytes/Molecular Reflex, Whole Blood:
-This is the recommended test for carrier testing for Tay-Sachs disease and Sandhoff disease.
-Testing begins with hexosaminidase A and total enzyme analysis. If the results are consistent with an affected or carrier for Tay-Sachs disease or Sandhoff disease, next generation sequencing to detect single nucleotide and copy number variants for HEXA or HEXB, respectively, will automatically be performed on the original specimen.
-This test is appropriate for males and pregnant or nonpregnant females.
NAGW / Hexosaminidase A and Total Hexosaminidase, Leukocytes:
-This test can be used for diagnosis and carrier testing for Tay-Sachs disease or Sandhoff disease.
-Results for hexosaminidase A and total enzyme analysis are reported with recommendations for additional testing when appropriate. All follow-up testing must be ordered separately on new specimens.
-This test is appropriate for males and pregnant or nonpregnant females.
NAGS / Hexosaminidase A and Total Hexosaminidase, Serum:
-This test can be used for diagnosis and carrier testing for Tay-Sachs disease or Sandhoff disease.
-Results for hexosaminidase A and total enzyme analysis are reported with recommendations for additional testing when appropriate.
-If results indicate normal, indeterminate, or carrier status and the suspicion of Tay-Sachs disease remains high, MUGS / Hexosaminidase A, Serum for Tay-Sachs disease (B1 variant) can typically be added and performed on the same specimen.
-With the exception of MUGS, all follow-up testing must be ordered separately on new specimens.
-This test is not appropriate for pregnant females or women receiving hormonal contraception. This test is appropriate for males and nonpregnant females.
-This test is particularly useful when it is difficult to obtain enough blood to perform leukocyte testing (NAGR or NAGW), as may be the case with infants.
MUGS / Hexosaminidase A, Serum:
-This is the recommended test for diagnosis and carrier testing for the B1 variant of Tay-Sachs disease. This test will not detect Sandhoff disease.
-This test should not be ordered as a first-line test. Rather, this test should be ordered when the NAGR, NAGW, NAGS indicate normal, indeterminate, or carrier results and the suspicion of Tay-Sachs disease remains high. In most cases, this test can be performed on the original specimen collected for NAGS.
Specimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions: Centrifuge and aliquot serum into plastic vial.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Frozen (preferred) | 30 days | |
| Refrigerated | 7 days |
Special Instructions
Reference Values
Hexosaminidase total
≤15 years: ≥20 nmol/min/mL
≥16 years: 10.4-23.8 nmol/min/mL
Hexosaminidase percent A
≤15 years: 20-90%
≥16 years: 56-80%
Day(s) Performed
Thursday
CPT Code Information
83080 x 2
Method Description
The hexosaminidases are among the more active of the lysosomal enzymes, which hydrolyze derivatives of beta-D-N-acetylglucosamine and beta-D-N-acetylgalactosamine. Natural substrates are certain sphingolipids (ie, GM2) in which acetylgalactosamine is the terminal monosaccharide. The 2 hexosaminidase isoenzymes, A and B, differ in their electrophoretic mobility and heat stability. Hexosaminidase A moves toward the anode and is heat labile, while hexosaminidase B moves toward the cathode and is heat stable.
The procedure is performed using an automated pipetting station and a spectrophotometer. The substrate used is 4-methylumbelliferyl-N-acetyl-beta-D-glucopyranoside (4-MUF-acetamido-2-deoxy-beta-D-glucopyranoside) from which the fluorescent compound, 4-methylumbelliferone, is liberated by both hexosaminidases.
The sample is mixed with citrate phosphate buffer and mixture is separated into 2 tubes. One tube stays at ambient temperature and the other is heated at 51.5° C for 15 minutes. On the automated pipetting station, sample and substrate are pipetted into a microtiter test tube located in a 37 degree C waterbath. The hexosaminidase A fraction is destroyed in the heated sample, leaving only hexosaminidase B to react with the substrate. The unheated sample provides the total hexosaminidase (A and B). The reaction is stopped with glycine after the 30-minute incubation. Sample intensities are compared to that of a 4-methylumbelliferone standard curve to quantitate both the total and the B fraction. The percentage of the A fraction that was inactivated by heating is calculated based on these results. The difference in heat inactivation is used to fractionate hexosaminidase activities.(O'Brien JF, Burtis CA, Ashwood ER: Lysosomal storage diseases. In: Tietz Textbook of Clinical Chemistry. 2nd ed. WB Saunders Company; 1994:2149-2160; Cowan T, Pasquali M: Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KD, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw-Hill; 2017:1139-1158)
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | Reject |
Method Name
Heat Inactivation, Fluorometric, Automated
Testing Algorithm
For more information see Tay-Sachs and Related Disorders Diagnostic Testing Algorithm
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. Biochemical Genetics Patient Information (T602)
3. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.