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CPT 81109: HPA-5 (K505E) Genetic Analysis

CPT code 81109 represents a molecular diagnostic laboratory test that analyzes the HPA–5 (K505E) alleles to determine platelet antigen status. This genetic analysis has clinical relevance for transfusion medicine, platelet compatibility assessment, and certain prenatal scenarios where fetal platelet antigen typing may inform clinical decisions. Nationally, such targeted genetic tests contribute to precision transfusion practices and perinatal risk assessment.

Key payers included in the coverage discussion are Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of the code’s clinical context, how and where the test is typically performed, and the practical implications for laboratory services. The publication also summarizes benchmarking and coverage considerations, coding and billing basics, and common clinical scenarios in which CPT code 81109 is used.

This resource is intended to provide a clear, national-level briefing on the purpose of CPT code 81109, the clinical settings in which the test is ordered, and the types of information stakeholders should expect when evaluating laboratory genetic testing for HPA–5 (K505E). Data not available in the input will be noted where applicable.

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Billing Code Overview

CPT code 81109 describes a laboratory molecular diagnostic test that analyzes the genes for the two common alleles of Human Platelet Antigen 5 (HPA–5), also known as K505E, using a biological specimen such as blood or amniotic fluid. The procedure involves technical laboratory work to identify allele variants relevant to platelet antigen status.

Service type: Molecular diagnostic genetic test (technical component)
Typical site of service: Clinical laboratory or reference molecular diagnostics laboratory; specimen collection may occur in outpatient phlebotomy settings or obstetric care settings for amniotic fluid specimens.

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CPT 81109: HPA-5 (K505E) Genetic Analysis

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Billing Code Overview

Service type: Molecular diagnostic genetic test (technical component)
Typical site of service: Clinical laboratory or reference molecular diagnostics laboratory; specimen collection may occur in outpatient phlebotomy settings or obstetric care settings for amniotic fluid specimens.

Clinical & Coding Specifications

Clinical Context

A typical patient is a pregnant woman or an adult being evaluated for alloimmune thrombocytopenia risk or transfusion compatibility. A prenatal obstetrician orders 81109 when a patient has a prior history of neonatal alloimmune thrombocytopenia (NAIT), unexplained fetal thrombocytopenia, a previous infant with intracranial hemorrhage, or when the partner’s or fetus’s platelet antigen status is needed for risk assessment. The clinical workflow begins with collection of a maternal peripheral blood sample (or amniotic fluid when fetal testing is indicated) and submission to a molecular diagnostics laboratory. The laboratory analyst performs DNA-based genotyping to determine the allelic variants of Human Platelet Antigen 5 (HPA–5, K505E). Results are reported to the ordering clinician and used to counsel regarding recurrence risk, guide monitoring in pregnancy, plan for peripartum management, and inform transfusion or platelet selection decisions for the mother or neonate.

Coding Specifications

Modifier	Description	When to Use
`11`	Normal, expected performance of the service	Use when `81109` is performed without unusual circumstances and billing as primary service.
`22`	Increased procedural services	Use when the testing required substantially greater effort or complexity than typical (e.g., extensive validation for a rare specimen).
`26`	Professional component	Use when billing only the professional component (interpretation) separate from the technical laboratory work.
`52`	Reduced services	Use when the test is partially completed or limited in scope.
`53`	Discontinued procedure	Use if specimen collection or processing was started but testing could not be completed for clinical reasons.
`59`	Distinct procedural service	Use when `81109` is a distinct service from another procedure provided on the same day (e.g., separate genotyping panel).
`62`	Two surgeons/performing providers	Rare for this lab-based code; use only if two qualified providers share responsibility for the testing process per payer rules.
`90`	Reference laboratory outside the billing entity	Use when the testing is performed by an outside reference laboratory and only technical component or pass-through billing applies.
`TC`	Technical component	Use when billing only the technical component (laboratory processing) of `81109`.

Taxonomy Code	Specialty	Notes
`0000A`	Clinical Molecular Genetics Laboratory	Molecular diagnostics labs perform `81109` testing; local coding systems will vary.
`0000B`	Pathology - Clinical Molecular Pathology	Pathology departments that manage molecular testing and result interpretation.
`0000C`	Obstetrics & Gynecology	Ordering providers for prenatal risk assessment and management of alloimmune thrombocytopenia.
`0000D`	Maternal-Fetal Medicine	Specialists who order fetal platelet antigen testing for high-risk pregnancies.
`0000E`	Transfusion Medicine/Immunohematology	Specialists coordinating platelet selection and transfusion management based on HPA genotypes.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`D69.5`	Secondary thrombocytopenia	Evaluated when maternal or fetal thrombocytopenia is identified and HPA genotyping helps determine alloimmune causes.
`O36.5XX0`	Maternal care for known or suspected fetal abnormality and damage, unspecified trimester	Used when fetal platelet antigen testing is ordered as part of fetal abnormality assessment (e.g., suspected fetal thrombocytopenia).
`O36.5920`	Maternal care for known or suspected fetal abnormality, suspicion of genetic condition, first trimester	Applied when prenatal genotyping for platelet antigens is sought to assess fetal risk.
`Z36.0`	Encounter for antenatal screening for chromosomal anomalies (used as prenatal screening visit code)	Used when HPA genotyping is part of targeted prenatal screening after prior affected pregnancy.
`Z39.2`	Encounter for routine postpartum follow-up following delivery	Postnatal genotyping may be performed to clarify neonatal thrombocytopenia etiology and guide future pregnancy counseling.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`81479`	Unlisted molecular pathology procedure	Used when a specific genetic test does not have an assigned code; sometimes used for novel or expanded platelet antigen panels alongside `81109`.
`88237`	Flow cytometry, DNA analysis, probe-based (for platelet antigen surface testing)	May be used when platelet antigen expression testing is performed by flow cytometry rather than genotyping; complementary to `81109` when phenotype confirmation is required.
`36415`	Collection of venous blood by venipuncture	Often performed immediately prior to `81109` specimen submission for DNA-based HPA–5 testing.
`0000F`	Maternal cell-free DNA fetal testing (placeholder)	In workflows where fetal genotyping is pursued noninvasively or via amniocentesis, relevant prenatal molecular tests may be ordered in coordination with `81109` results.
`89240`	Amniotic fluid genetic studies (processing)	When fetal testing for HPA alleles is performed on amniotic fluid, specimen processing and genetic analysis codes are part of the workflow.

CPT 81105: HPA-1 (CD61/ITGB3) Platelet Antigen Genotyping

CPT-81106-HPA-2-T145M-GENETIC-ALLELE-ANALYSIS

CPT 81106: HPA-2 (T145M) Genetic Allele Analysis

CPT-81107-HPA-3-GENETIC-ANALYSIS-TECHNICAL-COMPONENT

CPT 81107: HPA‑3 (I843S) Platelet Antigen Genotyping

CPT-81108-HPA-4-R143Q-GENOTYPING

CPT 81108: HPA-4 (R143Q) Genotyping, Technical Component

CPT-81110-HPA-6-R489Q-GENOTYPING

CPT 81110: HPA-6 (R489Q) Genotyping, Technical Component

CPT-81111-HPA-9-V837M-ALLELE-ANALYSIS

CPT 81111: HPA-9 (V837M) Allele Analysis, Laboratory Technical Component

CPT-81112-HPA-15-GENETIC-ANALYSIS-S682Y

CPT 81112: HPA-15 (S682Y) Genetic Analysis

CPT-81120-IDH1-MOLECULAR-DIAGNOSTIC-TEST

CPT 81120: IDH1 Molecular Diagnostic Test

CPT-81121-IDH2-MOLECULAR-DIAGNOSTIC-TEST

CPT 81121: IDH2 (NADP+) Molecular Diagnostic Test

CPT-81161-DMD-GENE-DELETION-DUPLICATION-ANALYSIS

CPT 81161: DMD Gene Deletion/Duplication Analysis

Showing 1–10 of 199

References

1.CPT® Codes and Descriptions. AAPC. Retrieved Jul 29, 2026.
2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Jul 29, 2026.
3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Jul 29, 2026.

Published by

Trek Health powers OpenPayer with a leading commercial payer intelligence platform, seamlessly converting fragmented payer data into actionable insights for provider organizations.

Trek Health ingests and normalizes Transparency in Coverage data and payer policy updates to give provider organizations a clear view of how commercial reimbursement behaves across markets, payers, and services. Our platform transforms raw payer disclosures into structured intelligence that supports contract evaluation, payer negotiations, and service line strategy. By combining market benchmarks with ongoing policy visibility, Trek helps teams identify variability, risk, and opportunity in commercial reimbursement. The result is faster insight, stronger negotiating positions, and more informed financial decisions.

Clinical & Coding Specifications

Clinical Context

Coding Specifications

Modifier	Description	When to Use
`11`	Normal, expected performance of the service	Use when `81109` is performed without unusual circumstances and billing as primary service.
`22`	Increased procedural services	Use when the testing required substantially greater effort or complexity than typical (e.g., extensive validation for a rare specimen).
`26`	Professional component	Use when billing only the professional component (interpretation) separate from the technical laboratory work.
`52`	Reduced services	Use when the test is partially completed or limited in scope.
`53`	Discontinued procedure	Use if specimen collection or processing was started but testing could not be completed for clinical reasons.
`59`	Distinct procedural service	Use when `81109` is a distinct service from another procedure provided on the same day (e.g., separate genotyping panel).
`62`	Two surgeons/performing providers	Rare for this lab-based code; use only if two qualified providers share responsibility for the testing process per payer rules.
`90`	Reference laboratory outside the billing entity	Use when the testing is performed by an outside reference laboratory and only technical component or pass-through billing applies.
`TC`	Technical component	Use when billing only the technical component (laboratory processing) of `81109`.

Taxonomy Code	Specialty	Notes
`0000A`	Clinical Molecular Genetics Laboratory	Molecular diagnostics labs perform `81109` testing; local coding systems will vary.
`0000B`	Pathology - Clinical Molecular Pathology	Pathology departments that manage molecular testing and result interpretation.
`0000C`	Obstetrics & Gynecology	Ordering providers for prenatal risk assessment and management of alloimmune thrombocytopenia.
`0000D`	Maternal-Fetal Medicine	Specialists who order fetal platelet antigen testing for high-risk pregnancies.
`0000E`	Transfusion Medicine/Immunohematology	Specialists coordinating platelet selection and transfusion management based on HPA genotypes.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`D69.5`	Secondary thrombocytopenia	Evaluated when maternal or fetal thrombocytopenia is identified and HPA genotyping helps determine alloimmune causes.
`O36.5XX0`	Maternal care for known or suspected fetal abnormality and damage, unspecified trimester	Used when fetal platelet antigen testing is ordered as part of fetal abnormality assessment (e.g., suspected fetal thrombocytopenia).
`O36.5920`	Maternal care for known or suspected fetal abnormality, suspicion of genetic condition, first trimester	Applied when prenatal genotyping for platelet antigens is sought to assess fetal risk.
`Z36.0`	Encounter for antenatal screening for chromosomal anomalies (used as prenatal screening visit code)	Used when HPA genotyping is part of targeted prenatal screening after prior affected pregnancy.
`Z39.2`	Encounter for routine postpartum follow-up following delivery	Postnatal genotyping may be performed to clarify neonatal thrombocytopenia etiology and guide future pregnancy counseling.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`81479`	Unlisted molecular pathology procedure	Used when a specific genetic test does not have an assigned code; sometimes used for novel or expanded platelet antigen panels alongside `81109`.
`88237`	Flow cytometry, DNA analysis, probe-based (for platelet antigen surface testing)	May be used when platelet antigen expression testing is performed by flow cytometry rather than genotyping; complementary to `81109` when phenotype confirmation is required.
`36415`	Collection of venous blood by venipuncture	Often performed immediately prior to `81109` specimen submission for DNA-based HPA–5 testing.
`0000F`	Maternal cell-free DNA fetal testing (placeholder)	In workflows where fetal genotyping is pursued noninvasively or via amniocentesis, relevant prenatal molecular tests may be ordered in coordination with `81109` results.
`89240`	Amniotic fluid genetic studies (processing)	When fetal testing for HPA alleles is performed on amniotic fluid, specimen processing and genetic analysis codes are part of the workflow.

CPT 81105: HPA-1 (CD61/ITGB3) Platelet Antigen Genotyping

CPT-81106-HPA-2-T145M-GENETIC-ALLELE-ANALYSIS

CPT 81106: HPA-2 (T145M) Genetic Allele Analysis

CPT-81107-HPA-3-GENETIC-ANALYSIS-TECHNICAL-COMPONENT

CPT 81107: HPA‑3 (I843S) Platelet Antigen Genotyping

CPT-81108-HPA-4-R143Q-GENOTYPING

CPT 81108: HPA-4 (R143Q) Genotyping, Technical Component

CPT-81110-HPA-6-R489Q-GENOTYPING

CPT 81110: HPA-6 (R489Q) Genotyping, Technical Component

CPT-81111-HPA-9-V837M-ALLELE-ANALYSIS

CPT 81111: HPA-9 (V837M) Allele Analysis, Laboratory Technical Component

CPT-81112-HPA-15-GENETIC-ANALYSIS-S682Y

CPT 81112: HPA-15 (S682Y) Genetic Analysis

CPT-81120-IDH1-MOLECULAR-DIAGNOSTIC-TEST

CPT 81120: IDH1 Molecular Diagnostic Test

CPT-81121-IDH2-MOLECULAR-DIAGNOSTIC-TEST

CPT 81121: IDH2 (NADP+) Molecular Diagnostic Test

CPT-81161-DMD-GENE-DELETION-DUPLICATION-ANALYSIS

CPT 81161: DMD Gene Deletion/Duplication Analysis

Showing 1–10 of 199

References

1.CPT® Codes and Descriptions. AAPC. Retrieved Jul 29, 2026.
2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Jul 29, 2026.
3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Jul 29, 2026.

Published by

Trek Health powers OpenPayer with a leading commercial payer intelligence platform, seamlessly converting fragmented payer data into actionable insights for provider organizations.

OpenPayer

CPT 81109: HPA-5 (K505E) Genetic Analysis

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Billing Code Overview

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CPT 81109: HPA-5 (K505E) Genetic Analysis

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Billing Code Overview

Clinical & Coding Specifications

Clinical Context

Coding Specifications

Related Diagnoses

Related CPT Codes

Related Codes

References

Clinical & Coding Specifications

Clinical Context

Coding Specifications

Related Diagnoses

Related CPT Codes

Related Codes

References