Hexosaminidase Testing



TSD (Tay-Sachs disease) testing.


To assist in diagnosing Tay-Sachs and Sandhoff disease by identifying a hexosaminidase enzyme deficiency.

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

Method: Fluorometry for enzyme assay, polymerase chain reaction (PCR)/primer extension for molecular assay.

Plasma Enzyme Assay Conventional UnitsPlasma Enzyme Assay SI Units (Conventional Units × 0.0167)
Hexosaminidase Total589–955 nmol/hr/mL9.83–15.98 nmol/hr/mL
Hexosaminidase A 55%–76% of total hexosaminidase55%–76% of total hexosaminidase
Whole blood leukocyte assay: greater than 62%Molecular assay: Negative for HEXA gene mutationsMolecular assay: Negative for HEXB variants
Methods vary, reference ranges vary; the reference range and interpretive summary provided in the laboratory report should be used to properly evaluate results. Carrier values are approximately half of the expected normal values.

Critical Findings and Potential Interventions


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