CPT® Code 81109

Official Description

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])

Common Language Description

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.

1. Indications

The Human Platelet Antigen 5 genotyping (HPA-5) test is indicated for several specific clinical scenarios, particularly related to conditions that affect platelet function and immune response. The following indications are explicitly provided:

Neonatal Alloimmune Thrombocytopenia (NAIT) - This condition arises when maternal antibodies target fetal platelets due to the presence of paternal alloantigens, leading to potential complications such as severe thrombocytopenia and intracranial hemorrhage.
Post-Transfusion Purpura - This condition occurs when a patient develops severe bleeding following a platelet transfusion that contains incompatible HPA or platelet-specific antigens, typically manifesting 5 to 10 days after the transfusion.
Fetal Alloimmunization Screening - The test may be used to screen for fetal alloimmunization during pregnancy, assessing the risk of NAIT in future pregnancies.
Maternal Risk Assessment - It is also utilized to evaluate the risk of NAIT in mothers who may have had previous pregnancies affected by alloimmunization.

2. Procedure

The procedure for Human Platelet Antigen 5 genotyping involves several critical steps to ensure accurate identification of the HPA-5 a/b allele variants. The following procedural steps are outlined:

Sample Collection - Blood, amniotic fluid, or cultured amniocytes are collected as the source material for testing. Each sample type must be obtained through a separately reportable procedure, ensuring that the correct specimen is used for analysis.
DNA Extraction - Once the samples are collected, DNA is extracted from the cells present in the blood, amniotic fluid, or cultured amniocytes. This step is crucial for isolating the genetic material needed for the subsequent analysis.
Multiplex Polymerase Chain Reaction (PCR) - The extracted DNA undergoes multiplex PCR, a technique that allows for the simultaneous amplification of multiple target sequences. This method is particularly effective for detecting specific alleles associated with the HPA-5 gene.
Allele-Specific Primer Extensions - Following amplification, allele-specific primer extensions are performed. This step involves using primers that are designed to bind specifically to the HPA-5 a/b alleles, facilitating the identification of the variants present in the sample.
Fluorescence Observation - The final step involves fluorescence observation, where the results of the PCR and primer extension reactions are analyzed. This allows for the determination of the presence of HPA-5 a/b variants based on the fluorescence signals generated during the process.

3. Post-Procedure

After the completion of the Human Platelet Antigen 5 genotyping procedure, the following post-procedure considerations are important:

Results from the genotyping test will be analyzed and reported to the healthcare provider, who will interpret the findings in the context of the patient's clinical situation. Depending on the results, further management may be required, particularly in cases of identified alloimmunization risks. Patients may need to be monitored for symptoms associated with NAIT or post-transfusion purpura, and appropriate interventions may be initiated based on the findings. Additionally, counseling may be provided to expectant mothers regarding the implications of the test results for future pregnancies.

Short Descr	HPA-5 GENOTYPING
Medium Descr	HPA-5 GENOTYPING GENE ANALYSIS COMMON VARIANT
Long Descr	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])
Status Code	Statutory Exclusion (from MPFS, may be paid under other methodologies)
Global Days	XXX - Global Concept Does Not Apply
PC/TC Indicator (26, TC)	9 - Not Applicable
Multiple Procedures (51)	9 - Concept does not apply.
Bilateral Surgery (50)	9 - Concept does not apply.
Physician Supervisions	09 - Concept does not apply.
Assistant Surgeon (80, 82)	9 - Concept does not apply.
Co-Surgeons (62)	9 - Concept does not apply.
Team Surgery (66)	9 - Concept does not apply.
Diagnostic Imaging Family	99 - Concept Does Not Apply
CLIA Waived (QW)	No
APC Status Indicator	Service Paid under Fee Schedule or Payment System other than OPPS
Type of Service (TOS)	5 - Diagnostic Laboratory
Berenson-Eggers TOS (BETOS)	none
MUE	1

90	Reference (outside) laboratory: when laboratory procedures are performed by a party other than the treating or reporting physician or other qualified health care professional, the procedure may be identified by adding modifier 90 to the usual procedure number.