Cystic Fibrosis (CF), 5T Allele Genotyping

CPT: 81224
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Test Details

Synonyms

  • 5T Allele Genotyping
  • CBAVD
  • Congenital Bilateral Absence of the Vas Deferens (CBAVD)

Use

Detect congenital bilateral absence of the vas deferens (CBAVD) (OMIM 277180); refine the clinical impact of an identified R117H CF mutation

Limitations

Routine screening for the 5T allele in the cystic fibrosis (CF) gene as part of standard CF carrier screening is not recommended since the goal of carrier screening is to identify couples at risk for having children with cystic fibrosis. The 5T allele is associated primarily with male infertility or atypical symptoms, although many individuals are asymptomatic. Analysis of the 5T allele may be a useful adjunct to the standard CF panel of 32 mutations (480533) in patients with male infertility or idiopathic pancreatitis. Genetic counseling is recommended for any person testing positive for the 5T variant.

Methodology

Polymerase chain reaction (PCR) and a solution-phase multiplex allele-specific primer extension with subsequent hybridization to a bead array followed by fluorescence detection.

Specimen Requirements

Specimen

Whole blood, amniotic fluid, chorionic villus sample (CVS) (submission of maternal blood is required for fetal testing), or LabCorp buccal swab kit (buccal swab collection kit contains instructions for use of a buccal swab)

Volume

7 mL whole blood, 10 mL amniotic fluid, 20 mg CVS, or LabCorp buccal swab kit

Minimum Volume

3 mL whole blood, 5 mL amniotic fluid, 10 mg CVS, or two buccal swabs

Container

Lavender-top (EDTA) tube, yellow-top (ACD) tube, sterile plastic conical tube or two confluent T25 flasks for fetal testing, or LabCorp buccal swab kit

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; one buccal swab; wet buccal swab

Clinical Information

Special Instructions

Whole blood tube should be sent to the lab unopened. It is preferable not to perform additional testing on original tubes prior to PCR testing. A completed screening questionnaire must accompany specimens. Call 800-345-4363 to request forms, or photocopy the Cystic Fibrosis Screening Questionnaire from the Genetics Appendix online.

References

American College of Obstetricians and Gynecologists Committee on Genetics. ACOG Committee Opinion N° 486: Update on carrier screening for cystic fibrosis. Obstet Gynecol. 2011 Apr; 117(4):1028-1031. 21422883
Chillón M, Casals T, Mercier B, et al. Mutations in the cystic fibrosis gene in patients with congenital absence of the vas deferens. N Engl J Med. 1995; 332(22):1475-1480. 7739684
Richards CS, Bradley LA, Amos J, et al. Standards and guidelines for CFTR mutation testing. Genet Med., 2002; 4(5):379-391; erratum: 2002; 4(6):471.12394352
Watson MS, Cutting GR, Desnick RJ, et al. Cystic fibrosis population carrier screening: 2004 revision of American College of Medical Genetics mutation panel. Genet Med. 2004; 6(5):387-391; erratum: Genet Med. 2004; 6(6):548; Genet Med. 2005; 7(4):286.15371902

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
480970 5T Allele Genotyping 480978 5T Allele Genotyping 34729-4
480970 5T Allele Genotyping 480977 Comment: N/A
480970 5T Allele Genotyping 511938 PDF Pending
480970 5T Allele Genotyping 480976 5T Allele Genotyping N/A

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