LabCorp and its Specialty Testing Group, a fully integrated portfolio of specialty and esoteric testing laboratories.

Zygosity Testing

CPT:

81265

Zygosity testing determines if the fetuses are identical or fraternal in a multiple gestation pregnancy. Zygosity testing is ordered for complicated multiple gestations.

Test Details

Use

Provide evidence that twins are monozygotic versus dizygotic.  

Methodology

Analysis of short tandem repeat markers by polymerase chain reaction (PCR) and capillary electrophoresis

Specimen Requirements

Specimen

Whole blood or mouthwash (see specimen kit for detailed instructions), amniotic fluid, chorionic villi.

Volume

Postnatal:  10 mL whole blood or mouthwash /Prenatal: 10 mL amniotic fluid in orange-top polypropylene tube, 10-15 mg chorionic villi in laboratory provided screw-top tubes with sterile transport medium or one T-25 flask of confluent cells. 

Container

Lavender-top (EDTA) tube or yellow-top (ACD-A) tube or mouthwash kit

Special Instructions

Prenatal testing: Integrated Genetics clients should call 800-848-4436 to speak to a laboratory genetic coordinator before collecting any specimens.   In some circumstances, specimens from other family members may be required. 

All prenatal specimens (including cord blood) must be accompanied by a maternal blood or mouthwash specimen for analysis of possible maternal cell contamination. 

Discard first 2 mL; then 10 mL amniotic fluid in 15 ml orange-top polypropylene tube, 10-15 mg chorionic villi in laboratory-provided screw-top tubes with sterile transport medium or one T-25 flask of confluent cells. 

Additional sample must be obtained for back-up culture at one of our cytogenetics laboratories or another facility.  If additional testing is desired, more amniotic fluid is needed. For example, chromosome analysis requires an additional 15-25 mL (see Cytogenetics – Amniotic Fluid Chromosome Analysis test page) and AFAFP requires an additional 2 mL (see Amniotic Fluid Alpha-Fetoprotein - AFAFP test page). 

Causes for Rejection

Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; unlabeled or mislabeled specimen

Storage Instructions

Maintain specimen at room temperature

Additional Information

Zygosity testing determines if the fetuses are identical or fraternal in a multiple gestation pregnancy. Zygosity testing is ordered for complicated multiple gestations.

Limitations

 False-positive and false-negative results may occur for reasons that include genetic variants, blood transfusions, bone marrow transplantation, erroneous representation of family relationships, or contamination of a fetal sample with maternal cells.

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