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Test Code HEX AB Ta Hexosaminidase Levels A+B

Clinical System Name

Hexosaminidase Levels A + B


I Cell Disease

Tay Sachs


GM2 gangliosidosis



Enzyme analysis of total hexosaminidase and % hexosaminidase A for diagnosis of GM 2 gangliosidosis (Tay-Sachs, Sandhoff) and evaluation of I-Cell disease.

Sample Requirements

Specimen: Whole Blood

Container(s): Dark Green/Sodium Heparin tube, Yellow/ACD A or B, Serum from Gold SST or Red top tubes

Preferred Vol:  2.0 mL

Minimum Vol: 1.0 mL


Note: Also acceptable: cultured cells from skin fibroblasts

Processing Instructions

Reject due to:

Spin: Y


Temp:-20 C

Storage location: Biochemical Genetics Box -20 C



Specimen should be spun and aliquoted within 2 hours of collection.



Off-site collection:  Transport  to Laboratory immediately.


Specimen Type Temperature Time
Aliquoted Serum/Plasma Refrigerated

7 days

  Freezer (-20 C)-preferred 1 month



STAT Performed TAT
N Weekly 7  days

Contact the Biochemical Genetics Lab for requests outside of stated availability (206)987-2216.

Performing Laboratory

Seattle Children's Laboratory    


Department:  Biochemical Genetics

Phone Number: 206-987-2216



Reference Range


Specimen Type Normal Range

Total hexosaminidase (serum)

932-1844 nmol/hr/mL
% Hex A 54.7 - 70%

Carrier testing not performed


Method:  Enzymatic/Fluorometric; 4-methylumbelliferyl substrate with heat inactivation

Analytical Volume:


CPT Codes


Special Instructions

Links to:

Consent Forms



Biochemical Genetics Requisition


On the requisition include clinical information needed for appropriate interpretation. (Age, gender, drug therapy and family history)

Clinical Utility

Hexosaminidase A deficiency results in a group of neurodegenerative disorders caused by the accumulation of a cellular lipid called GM 2 ganglioside. This glycosphingolipid accumulates in the lysosomes causing progressive weakness, neurological deterioration, seizures, loss of milestones and loss of vision.

The disorders range from acute infantile onset  (classic Tay Sachs disease) to juvenile, chronic and adult-onset forms. The diagnosis of hexosaminidase A deficiency is characterized by absent or profoundly deficient beta-hexosaminidase A activity in the presence of normal beta-hexosaminidase B activity.


Patients with I Cell disease (mucolipidosis type I or II) have extreme elevation of serum/plasma total hexosaminidase.


Carrier testing by enzyme analysis is not available.