CPT® Code 81108

Human Platelet Antigen 4 genotyping (HPA-4), ITGB3 (integrin, beta 3 [platelet glycoprotein IIIa], antigen CD61 [GPIIIa]) (eg, neonatal alloimmune thrombocytopenia [NAIT], post-transfusion purpura), gene analysis, common variant, HPA-4a/b (R143Q)

The CPT® Code 81108 refers to the gene analysis for Human Platelet Antigen 4 (HPA-4) genotyping, specifically targeting the ITGB3 gene, which encodes the integrin beta 3 protein, also known as platelet glycoprotein IIIa (CD61). This analysis is particularly relevant in the context of conditions such as neonatal alloimmune thrombocytopenia (NAIT) and post-transfusion purpura, both of which are associated with platelet alloantigens. The test focuses on identifying common variants of the HPA-4 allele, specifically the HPA-4a/b variant characterized by the R143Q single nucleotide polymorphism (SNP). Gene analysis is crucial for diagnosing and managing these conditions, as it helps in identifying specific HPA-4 variants that may lead to complications in neonates or during transfusions. NAIT occurs when maternal antibodies, specifically IgG, cross the placenta and target paternal alloantigens present on the fetal platelets, leading to severe thrombocytopenia and potential hemorrhagic complications. Symptoms of NAIT can manifest as severe low platelet counts, intracranial hemorrhage, and skin manifestations such as petechiae or purpura. On the other hand, post-transfusion purpura arises when a woman receives a platelet transfusion that contains incompatible HPA or platelet-specific antigens, resulting in a severe bleeding episode typically occurring 5 to 10 days post-transfusion. The identification of HPA-4 a/b allele variants is particularly significant, as studies indicate that these variants are present in approximately 80% of NAIT cases within the Asian population. The samples for this analysis can be obtained from blood, amniotic fluid, or cultured amniocytes, and the testing is performed using multiplex polymerase chain reaction (PCR) techniques, which involve allele-specific primer extensions and fluorescence detection to accurately identify the genetic variants present.