Tay-Sachs Screen with Reflex

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General Information

Lab Name
Lab Code
383
External Test Id
NAGR
Description

Useful For:

  • Carrier detection and diagnosis of Tay-Sachs disease
  • Recommended test for carrier detection of Tay-Sachs disease
  • Carrier detection and diagnosis of Sandhoff disease

Additional Test Information:

  • Testing begins with hexosaminidase A and total enzyme analysis. If the results are consistent with an affected or carrier individual, Tay-Sachs variant analysis will automatically be performed on the original specimen at additional charge.
  • This is not the recommended test for Sandhoff disease; however, if the results are suggestive of Sandhoff disease or carrier status, this will be indicated in the interpretive comment along with recommendations for additional testing. Follow-up testing for Sandhoff must be ordered separately.
  • This test is appropriate for males and pregnant or nonpregnant females.
  • If hexosaminidase A activity is below 63%, then molecular variant analysis will be performed at an additional charge.
  • Mayo Tay Sachs and Related Disorders Diagnostic Testing Algorithm

Ordering Notes: For Tay Sachs screen without reflex (Enzyme activity only), refer to Hexosaminidase A and Total, test guide 445. For Tay Sachs mutation analysis only, refer to test guide 384.

A completed Mayo Biochemical Genetics Patient Information Form is recommended, but not required.

Forms & Requisitions
Synonyms
Hexosaminidase A and Total with Molecular Reflex, Hexosaminidase A enzyme activity, NAGR, Tay-Sachs Carrier Testing
Components

Interpretation

Method

Heat Inactivation/Fluorometric/Semiautomated

Reference Range
Ref. Range Notes

Hexosaminidase Total:

< or =15 years: > or =20 nmol/min/mg
> or =16 years: 16.4-36.2 nmol/min/mg

Hexosaminidase Percent A:

Age

Reference Values
< or =15 years: > or =20 nmol/min/mg
> or =16 years: 16.4-36.2 nmol/min/mg

Interpretation:

Hexosaminidase A usually composes greater than 62% of the total hexosaminidase activity in leukocytes (normal = 63%-75% A).

In leukocytes, the percent Hex A is used in determining whether an individual is a carrier of or affected with Tay-Sachs disease:

  • 63% to 75% hexosaminidase A is normal (noncarrier)
  • 58% to 62% hexosaminidase A is indeterminate (molecular testing recommended to discern carriers from non-carriers and to allow for prenatal diagnosis if desired)
  • less than 58% hexosaminidase A is a carrier (molecular testing recommended to discern disease-causing variants from pseudodeficiency alleles and to allow for prenatal diagnosis if desired)
  • less than 20% hexosaminidase A is consistent with a diagnosis of Tay-Sachs disease.

In leukocytes, the total hexosaminidase in combination with the percent hexosaminidase A aids in determining whether an individual is at-risk to be a carrier of or is affected with Sandhoff disease:

  • greater than or equal to 76% hexosaminidase A is suggestive of a Sandhoff carrier, when the total hexosaminidase is depressed
  • Total hexosaminidase activity near zero with nearly 100% hexosaminidase A is consistent with Sandhoff disease

If hexosaminidase A activity is below 63%, then molecular variant analysis will be performed.

Interferences and Limitations

Cautions: A small percentage (<0.5%) of carriers may exhibit normal hexosaminidase A activity and will not be detected by this method.(1)

GM2 activator deficiency (GM2-gangliosidosis, AB variant) is a rare disorder with clinical features similar to Tay-Sachs and Sandhoff diseases; however, levels of both hexosaminidase A and B are normal. GM2 activator deficiency cannot be identified through testing offered at Mayo Clinic Laboratories.

Ordering & Collection

Specimen Type
Whole Blood
Collection

10 mL blood in YELLOW TOP (ACD) tube

  • ACD Solution B preferred; ACD Solution A accepted.
Forms & Requisitions
Handling Instructions

Outside Labortories: Store and transport whole blood at ambient temperature. Expedite transport to the lab. For optimal isolation of leukocytes, it is recommended the specimen arrive at Mayo within 6 days of collection to be stabilized (allow for transport time from UW-MT lab to Mayo).

Stability: Refrigerated (preferred): 6 days; Ambient: 6 days; Frozen: Unacceptable.

Reject Due To: Gross hemolysis.

Quantity
Requested: 10 mL whole blood
Minimum: 6 mL whole blood

Processing

Receiving Instructions

Refrigerate whole blood in original collection container.

Login: GSEND1-;REFRIG

  • GSNDT1: MAYO
  • GSTYP1: WB
  • GTSRQ1: ;Tay Sachs Screen with Reflex (Mayo Test NAGR)

Sendouts:

  • Order Mayo Test: NAGR.
  • Same day shipment is preferred. For optimal isolation of leukocytes, the specimen must arrive at Mayo within 6 days of collection to be stabilized.

Stability: Refrigerated (Preferred): 6 days; Ambient: 6 days; Frozen: Unacceptable.

Reject Due To: Gross hemolysis.

Misc Sendout

Performance

Lab Department
Frequency
Preanalytical processing occurs Monday through Saturday. Performed: Friday. Report Available: 4-8 days.
Available STAT?
No
Performing Location(s)
Sendout Mayo Clinic Laboratories
800-533-1710

200 First Street Southwest
Rochester, MN 55901

Billing & Coding

Billing Comments

CPTs: 83080x2

Potential Reflex Testing, if performed:

  • HEXA, Full Gene Analysis: 81479
  • HEXB, Full Gene Analysis: 81479

CAST: Add CASTRV for potential reflex testing.