Hexosaminidase A and B
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TSD (Tay-Sachs disease) testing.
To assist in diagnosing Tay-Sachs disease by identifying a hexosaminidase enzyme deficiency.
Serum collected in a yellow-top (acid-citrate-dextrose [ACD]) or a red-top tube for hexosaminidase enzyme assay; lavender-top (EDTA), pink-top (K2 EDTA) or yellow-top tube (ACD) for molecular polymerase chain reaction (PCR) assay.
(Method: Fluorometry for enzyme assay, 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).