G029 – Antithrombin III assay
OHIP Diagnostic & Therapeutic Procedures Code — DIAGNOSTIC AND THERAPEUTIC PROCEDURES · Schedule of Benefits
An antithrombin III assay, which is a laboratory service rendered by a physician, or a physician substitute, in the physician's own office for their own patient. This service is categorized under 'Reproductive medicine' and is generally only payable to physicians where point of care testing is a necessary component of their practice. The service is not insured when rendered to support in-vitro fertilization or artificial insemination services.
When to Use
- Use G029 for in-office point-of-care monitoring of patients on long-term anticoagulation therapy where immediate results are required for clinical management.
- Use this code when the assay is performed as a diagnostic necessity for a patient with suspected hereditary or acquired antithrombin deficiency outside of a fertility clinic setting.
Common Pitfalls
- Billing G029 for any patient undergoing IVF or artificial insemination will result in automatic claim rejection under Regulation 552.
- Submitting G029 when the test is performed at an external private laboratory rather than in your own office will lead to audit recovery, as these services are governed by the Schedule of Benefits for Laboratory Services.
Billing Tips
- Ensure your clinical notes explicitly link the test result to a specific treatment decision, such as a dosage adjustment, to satisfy the mandatory documentation requirements for this diagnostic procedure.
Effective: April 1, 2026
J. Diagnostic and Therapeutic Procedures
DIAGNOSTIC AND THERAPEUTIC PROCEDURES
Laboratory
Diagnostic and Therapeutic Procedures
The result of the test(s), the physician's interpretation of the results of the test(s) and the treatment decision based on the test results must be documented in the patient's permanent medical record.
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