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Twin Zygosity

CPT Code(s): 81265, 81266

Ordering Recommendation: Provide evidence that twins are monozygotic versus dizygotic. This test may be used for legal purposes, obstetric management, as part of a transplant evaluation, and for other purposes.

Synonyms: Identical twins, fraternal twins, monozygotic twins, dizygotic twins, identity testing, zygosity studies

Methodology: PCR followed by capillary electrophoresis using 15 autosomal short tandem repeat (STR) markers and one gender marker (amelogenin).

Performed: Monday through Friday

Reported: 6-9 days

Specimen Requirements

Collect: Blood: Lavender (EDTA) tubes; DNA: Screw cap tube, buccal swab (lab provides collection tube)

Specimen Volume: Blood: 2-6 mL whole blood; DNA: at least 0.55µg of genomic DNA at a concentration of at least 20 ng/µl; buccal swab

Storage/Transport: Refrigerated/Room temperature

Unacceptable Conditions: Grossly hemolyzed or clotted

Stability: Two weeks refrigerated; One month frozen