What the SA Modifier Actually Is

The SA modifier is an HCPCS Level II code. It identifies a service performed by a nurse practitioner (NP) under a physician’s supervision. Use SA when billing the NP’s work incident to the physician’s service. The claim goes under the physician’s NPI, not the NP’s.

The modifier tells the payer: “An NP did this work. A physician was present in the office suite. The service followed an established treatment plan.

When to Use SA Modifier 

Use the SA modifier only when all four conditions below are met. Missing even one means no SA modifier. Bill under the NP’s own NPI instead (reimbursement drops to 85% instead of 100% ).

Condition 1: The physician established the initial treatment plan. The NP is following that plan, not creating a new one.

Condition 2: The physician is physically present in the office suite during the NP’s service. Not on call. Not down the street. Same suite.

Condition 3: The NP performs the service within the state’s scope of practice laws. Full practice authority states do NOT automatically qualify for incident-to billing.

Condition 4: The payer requires SA modifier for incident-to claims. If the payer does not recognize SA, omit it. Medicare ignores SA. Some commercial payers deny claims without SA.

Denial alert: Missing condition #2 (physician presence) triggers recoupment up to 6 years retroactively. OIG targets this in 2026 audits.

Payer Requirements — How to Verify Instead of Guess

Do not assume any payer’s SA modifier policy. Policies change. Your job is to verify before you bill.

Step 1 — Check the payer’s provider manual:

Search for these terms in the manual:

• “Modifier SA”
• “Incident-to billing requirements.
• Nurse practitioner billing under the physician’s NPI

Step 2 — Look for three specific answers:

Step 3 — Document your findings:

Create a one-page reference sheet for each payer you bill. Update it quarterly. Include:

• Payer name
• Date verified
• SA required? (Yes/No)
• Incident-to allowed? (Yes/No)
• Link to manual page

Step 4 — When in doubt, call the provider line:

Ask: “Does your plan require modifier SA for incident-to services performed by a nurse practitioner and billed under the supervising physician’s NPI?”

Get the representative’s name and reference number. Document it.

Common patterns (verify each):

Do not copy another practice’s payer map. Their contracts may differ from yours.

Medicare’s Regional Differences That No One Else Tells You

Medicare does not require the SA modifier. But each MAC has different rules for NPP incident-to billing. Ignore these, and your claim gets CO-109 (Claim not processed by this MAC).

Below is the MAC map as of May 2026. Use this when submitting incident-to claims under the physician’s NPI.

Appeal address: Send to your MAC’s address on the remittance advice. Not CMS central. Returned unprocessed within 30 days if sent wrong.

SB Modifier Comparison — SA vs SB vs U7

Coders confuse SA, SB, and U7 regularly. Below is the distinction. Use the wrong modifier, and the payer denies with CO-16 (Claim lacks required modifier). 

Critical distinction — Do not swap SA and U7:

• SA = NP only. Do not use for PAs.
• U7 = PA only. Do not use for NPs.
• SB = CNM only. Do not use for routine primary care visits.

Payer-specific trap: Some Medicaid plans require U7 for PAs but SA for NPs on the same claim type. Run separate modifier logic by provider credential, not by service type.

Example of correct modifier selection: 

Denial fix: If you receive CO-16 (missing/invalid modifier), determine which modifier the payer requires for that provider type. Resubmit with the correct modifier. Appeal deadline: 180 days. 

Incident-to vs Direct Billing — The 85% vs 100% Decision

Final Thoughts 

You now have the tools: denial code table, MAC map, appeal letter template, and audit checklist. Use them. But tools alone do not fix denials. Consistent application requires dedicated resources. Many practices outsource this complexity.

iRCM provides denial management services that identify root causes, resolve disputes, and ensure timely appeals. Their team tracks payer policy changes, including SA modifier requirements, so you do not have to run quarterly reviews yourself. With AAPC-certified coders and full HIPAA/CMS compliance, iRCM handles SA modifier claims from submission through appeal.