Hexosaminidase A is a test performed to determine the presence of the lysosomal disease known as Tay-Sachs, a genetic autosomal recessive condition characterized by early and progressive retardation in the mental and physical development of the infant, with death resulting by the third or fourth year of life. The deficiency of this enzyme is most common in families of Eastern-European Jewish and French-Canadian origin. Because of this deficiency, gangliosides or complex sphingolipids are not metabolized and accumulate in the brain, causing the paralysis, blindness, dementia, and mental retardation that develop in the children who have this disorder.³⁶

• 56-80 percent of a total normal level (10.4-23.8 U/L)

• Pregnancy decreases the level of hexosaminidase in relation to the total, resulting in an inaccurate false positive.
• Oral contraceptives can decrease the level.

• Screening young adults for asymptomatic possession of this gene with or without a family history of Tay-Sachs disease
• Identifying carriers in high-risk clients during prenatal examination, revealed by a lowered enzyme activity
• Diagnosing Tay-Sachs in infants, revealed by a very low level or absence of enzyme activity
• In utero prenatal diagnosis of amniotic fluid or cells obtained from chorionic villi

Nursing Care Before the Procedure

Client preparation is the same as that for any test involving the collection of a peripheral blood sample (see Appendix I).

• Food and fluids should be avoided for 8 hours before the test, and oral contraceptives should be withheld.

A venipuncture is performed and the sample collected in a red-topped tube. Refer to the procedures to obtain prenatal samples via chorionic villus biopsy or amniocentesis (see Chapters 10 and 14).

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume any drugs withheld before the test.
• Complications and precautions: Recommend special genetic counseling for those with a family history of the disease or with abnormal test results.