CPT® Code 81111

Human Platelet Antigen 9 genotyping (HPA-9w), ITGA2B (integrin, alpha 2b [platelet glycoprotein IIb of IIb/IIIa complex, antigen CD41] [GPIIb]) (eg, neonatal alloimmune thrombocytopenia [NAIT], post-transfusion purpura), gene analysis, common variant, HPA-9a/b (V837M)

The CPT® Code 81111 refers to the gene analysis for Human Platelet Antigen 9 (HPA-9) genotyping, specifically targeting the ITGA2B gene, which encodes the integrin alpha 2b, a component of the platelet glycoprotein IIb/IIIa complex, also known as antigen CD41. 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 aims to identify specific variants of the HPA-9 allele, namely HPA-9a and HPA-9b, which are determined by a common variant known as V837M. Gene analysis for HPA-9 variants is crucial for diagnosing and managing conditions where maternal antibodies may target fetal platelets, leading to significant clinical consequences. In NAIT, maternal IgG antibodies can cross the placenta and attack the paternally inherited alloantigens present on the fetal platelets, resulting in severe thrombocytopenia and potential complications such as intracranial hemorrhage, petechiae, and visceral hemorrhage. Similarly, post-transfusion purpura can occur when a woman receives a platelet transfusion that contains incompatible HPA or platelet-specific antigens, leading to severe bleeding episodes typically occurring 5 to 10 days post-transfusion. The analysis can be performed on various sample types, including whole blood, amniotic fluid, or cultured amniocytes, and utilizes advanced techniques such as multiplex polymerase chain reaction (PCR) with allele-specific primer extensions and fluorescence observation to detect the presence of these genetic variants. This testing is essential for identifying at-risk neonates, screening for fetal alloimmunization during pregnancy, and assessing maternal risk for future pregnancies or transfusion-related complications.