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Huntington's Disease Triplet Repeat

Item Value
Approval req'd? No
Available Stat? No
Utilization Guidelines Tests with long turn-around times (ie. Molecular based tests and Microarrays) should only be requested on an inpatient if the result is going to affect the inpatient management.

If the patient will likely be discharged before the result will be available, the test should be requested after discharge. (NOTE: UCSF Medical Center is not reimbursed for inpatient testing).

An exception to the above may be appropriate if there is a possibility the patient will not survive to be discharged and the information is important for diagnosis and/or family decisions/management (ie. recurrence risk).
Test code HUNT
Performed by Medical Genomics - Molecular Diagnostics
In House Availability Run once per 1-2 weeks or as needed
Method PCR and capillary electrophoresis. Reflex to genomic Southern blot, if homozygosity is detected by PCR.
Collection Instructions All patients must receive genetic counseling prior to pre-symptomatic Huntingtons testing. The name of the genetic counselor who provided counseling must be included on the test requisition. For genetic counseling questions, contact Jamie Fong at 476-8613.

If collecting in citrate, check the expiration date on the label of the blue top vacutainer before drawing the patient.

Do not collect sample in heparin. Keep sample refrigerated for overnight or longer storage.

For UCSF Samples (from remote sites) Click here for sample collection instructions

For NON-UCSF Samples Click here for Requisition form & Account set-up instructions. Note we only do institutional billing.
Container type Lavender top preferred, Blue top and Yellow (ACD) tops acceptable
Amount to Collect 3 mL blood
Sample type EDTA, citrated or ACD whole blood
Preferred volume 3 mL blood
UCSF Rejection Criteria Inadequate sample. Samples collected in heparin.
Processing notes Do not centrifuge the specimen. Store at room temperature. Refrigerated samples are acceptable.
Normal range Normal, CAG repeat sizes less than 27.
Synonyms Huntington chorea; HTT
Turn around times 10-14 days
Additional information An interpretation of this test by a laboratory physician will automatically be performed and billed for separately.

The results for this test will not be available in APEX to safeguard patient confidentiality. All Huntington's results are referred to Genetic Counselor Jamie C. Fong and must be obtained from her at (415) 476-8613.

Results are reported as in the Table below following recommendations from the American College of Medical Genetics and Genomics (Bean L, Bayrak-Toydemir P. Genet. Med 16:1-7, 2014, PMID: 25356969).

CAG repeat size Interpretation
Less than 27 Normal allele
27 - 35 Normal mutable allele
36 - 39 HD allele with reduced penetrance
> 39 HD allele with full penetrance

This test was developed and its performance characteristics determined by the Clinical Laboratories at the Medical Center at UC San Francisco. It has not been cleared or approved by the U.S. Food and Drug Administration.
CPT coding 81401
LOINC code 53782-9
LDT or Mod FDA? Yes
Last Updated 2/21/2017 6:04:05 PM
Entry Number 539
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