NAGS - Performance: Hexosaminidase A and Total Hexosaminidase, Serum

Test Catalog

Test Name

Test ID: NAGS    
Hexosaminidase A and Total Hexosaminidase, Serum

Method Description Describes how the test is performed and provides a method-specific reference

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 two 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 degrees 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: Lysosomal storage diseases. In Tietz Textbook of Clinical Chemistry. Edited by CA Burtis, ER Ashwood. Second edition. Philadelphia, PA, WB Saunders Company, 1994 pp 2149-2160)

PDF Report Indicates whether the report includes an additional document with charts, images or other enriched information


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.

Varies; 10 a.m.

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.

8 days

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

15 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

30 days

Performing Laboratory Location The location of the laboratory that performs the test