Billing modifiers in Alberta's Schedule of Medical Benefits (SOMB) adjust the base fee for a service code based on circumstances like time of day, care setting, procedure complexity, or provider context. Applying the right modifiers is one of the most common areas where Alberta physicians leave revenue behind — or create audit exposure.
This page covers the modifier types available in Alberta SOMB billing, when they apply, and common mistakes to avoid.
A modifier is an add-on to a billing code that adjusts the fee paid for that service. Modifiers don't change what was done — they change the circumstances under which it was done. In Alberta, modifiers can increase the fee (e.g., after-hours premiums) or qualify a code for a specific context (e.g., anaesthesia involvement).
| Modifier | What it covers | Key rule |
|---|---|---|
| SURT | Surgical premium for eligible procedures | Applies to specific Health Service Codes (HSCs) only — limited to 6 eligible HSCs per SOMB rules. Not applicable to obstetric codes. |
| CMGP | Complexity modifier for general practice | Used for complex clinic encounters exceeding normal scope. Documentation must support the complexity claim. |
| After-hours | Time-band premiums (evenings, nights, weekends, holidays) | Specific time bands define eligibility. Not all codes qualify. Weekend and holiday rates differ from weekday evening rates. |
| CALL | On-call availability and callback | Applies when physician is called back for patient care. Distinct from after-hours — CALL covers the callback itself. |
| ANES | Anaesthesia-related modifiers | Applies to anaesthesia services with base unit + time unit fee structure. Procedure-specific rules apply. |
| HOSP | Hospital setting modifier | Adjusts fees for services provided in a hospital vs. office setting where applicable. |
| TELE | Telehealth/virtual care | Applies to eligible codes delivered via telephone or video. Not all codes are telehealth-eligible. |
| BMI | Body mass index complexity | Applies to specific procedural codes where patient BMI affects complexity. |
| BILATERAL | Bilateral procedure modifier | Applies when same procedure is performed on both sides. Fee adjustment varies by code. |
| ASSIST | Surgical assistant modifier | Applies when physician acts as surgical assistant. Specific assistant fee rates apply. |
Physicians working evenings, weekends, or holidays frequently forget to apply after-hours modifiers, especially when billing is done the next day. The time band of the encounter — not the time of billing — determines eligibility.
The SURT modifier is limited to specific Health Service Codes. Applying it to codes outside the eligible list creates audit risk. This is a common error in surgical billing.
The CMGP modifier requires documentation that supports the complexity claim. Applying CMGP without chart evidence is a frequent audit trigger for GPs.
When the same procedure is performed on both sides (e.g., bilateral knee injections), the bilateral modifier should be applied. This is commonly missed in orthopaedic and surgical encounters.
CALL modifiers and after-hours modifiers serve different purposes. Being on call doesn't automatically trigger after-hours premiums, and after-hours encounters don't automatically qualify for CALL billing.
Some modifiers can be combined on the same billing code (e.g., after-hours + hospital setting), while others are mutually exclusive or have specific stacking rules. The interaction between modifiers is one of the most complex areas of Alberta billing — and one where structured review catches errors that manual review misses.
ABPhysCode reviews encounter details against Alberta SOMB modifier rules and flags: