Davis's Lab & Diagnostic Tests
Hexosaminidase A and B
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Synonym/Acronym:
TSD (Tay-Sachs disease) testing.
Rationale
To assist in diagnosing Tay-Sachs 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.
| Total Hexosaminidase | Conventional Units | SI Units (Conventional Units × 0.0167) |
|---|---|---|
| Noncarrier | 589–955 nmol/hr/mL | 9.83–15.95 units/L |
| Heterozygote | 465–675 nmol/hr/mL | 7.77–11.27 units/L |
| Tay-Sachs homozygote | Greater than 1,027 nmol/hr/mL | Greater than 17.15 units/L |
| Hexosaminidase A | Conventional Units | SI Units (Conventional Units × 0.0167) |
| Noncarrier | 456–592 nmol/hr/mL or 55–76% of total hexosaminidase | 7.62–9.88 units/L or 55–76% of total hexosaminidase |
| Heterozygote | 197–323 nmol/hr/mL | 3.29–5.39 units/L |
| Tay-Sachs homozygote | 0 nmol/hr/mL | 0 units/L |
| Hexosaminidase B | Conventional Units | SI Units (Conventional Units × 0.0167) |
| Noncarrier | 12–32 nmol/hr/mL | 0.2–0.54 units/L |
| Heterozygote | 21–81 nmol/hr/mL | 0.35–1.35 units/L |
| Tay-Sachs homozygote | Greater than 305 nmol/hr/mL | Greater than 5.09 units/L |
Molecular assay: Negative for HEXA 7 mutations (samples are evaluated for seven specific HEXA gene mutations).
Critical Findings and Potential Interventions
N/A
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