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Billing code

A621A — Complex Medical Specific Re-assessment

Complex clinical immunology re-assessment

Bill A621 when a clinical immunologist re-assesses a patient because the condition is complex, obscure or serious.

Watch for: Send your findings in writing to the primary care physician, or it pays as a lesser assessment; limit 4 per 12 months.

Code

A621A

Description

Complex Medical Specific Re-assessment

FHO+ basket

Not in the FHO+ base rate basket (Schedule 2 or 2B).

Effective date

Apr 1, 2026

Termination date

No end date

Explanation

Updated October 26, 2026

Clinical immunology re-assessment for a complex, obscure or serious condition, with a written report to the primary care physician. Four per 12 months.

What it covers

A621 is the complex medical specific re-assessment in the Clinical Immunology (62) listing (A83). It is a re-assessment because of the complexity, obscurity or seriousness of the patient's condition and includes all the requirements of a medical specific re-assessment (GP24).

Billing rules

• You must report your findings, opinions or recommendations in writing to the patient's primary care physician, or it pays as a lesser assessment (GP24).
• Maximum 4 per patient per physician per 12 months; extra ones pay as a lesser assessment (GP24).
• A621 and medical specific assessments (A623) combined are also limited to 4 per patient per physician per 12 months (GP24).
• In hospital in-patients, bill C621 (A84).
• No other Consultations and Visits service is payable for the same patient on the same day as A620 (initiation of food allergy immunotherapy) or K621 (FAIT support) (A83, A84).
• Can be billed by video or telephone as comprehensive virtual care when an existing patient-physician relationship exists, with K300A or K301A; telephone pays 85% (AJ1, A66, A70).

Often billed with

• E078 chronic disease assessment premium (+50%) in the office or a hospital out-patient clinic (not the ED), for an established chronic disease with a GP26 diagnostic code on the claim (A83, GP25-GP26).

Common rejections

• EQ2: The specialty code on the claim wasn't registered and active for the physician on the service date. Correct it, or update the registration, then resubmit.
• EH2: The health card version code on the claim doesn't match OHIP's record, often because the patient has a newer card; get the current version code and resubmit.
• A4D: A621 is in the Clinical Immunology (62) listing, and specialists bill consultations and visits from their own specialty's listing (GP9). A claim under another registered specialty rejects; bill that specialty's code instead.

Related codes: A624, A623, A628, E078, C621

Source: Schedule of Benefits (July 1, 2026), Consultations and Visits, Clinical Immunology (62), pages A83-A84; General Preamble GP23-GP24 (complex medical specific re-assessment)

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