CPT® Code 81109

Human Platelet Antigen 5 genotyping (HPA-5), ITGA2 (integrin, alpha 2 [CD49B, alpha 2 subunit of VLA-2 receptor] [GPIa]) (eg, neonatal alloimmune thrombocytopenia [NAIT], post-transfusion purpura), gene analysis, common variant (eg, HPA-5a/b [K505E])

The CPT® Code 81109 refers to the gene analysis for Human Platelet Antigen 5 (HPA-5) genotyping, specifically targeting the ITGA2 gene, which encodes the alpha 2 subunit of the VLA-2 receptor. 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 HPA-5 gene analysis aims to identify specific variants, notably the HPA-5a/b alleles, which can have significant implications for patient management. The presence of single nucleotide polymorphisms (SNPs) in genes responsible for coding platelet membrane glycoproteins can lead to the development of these alloantigens. The test is utilized to identify HPA-5 variants in symptomatic neonates, to screen for fetal alloimmunization during pregnancy, and to evaluate the risk of NAIT in future pregnancies or post-transfusion purpura. NAIT is a condition where maternal IgG antibodies cross the placenta and target paternally inherited alloantigens on fetal platelets, potentially leading to severe complications such as thrombocytopenia and intracranial hemorrhage. In contrast, post-transfusion purpura occurs when a woman receives a platelet transfusion that contains incompatible HPA or platelet-specific antigens, resulting in severe bleeding episodes typically occurring 5 to 10 days post-transfusion. The identification of HPA-5 a/b allele variants is crucial, as these variants are associated with less severe episodes of NAIT. The samples for this analysis can be obtained from blood, amniotic fluid, or cultured amniocytes, which must be reported separately. The testing process employs multiplex polymerase chain reaction (PCR) techniques, utilizing allele-specific primer extensions and fluorescence observation to accurately detect the presence of these genetic variants.