Medical Billing Expert Witness Insights – Incident to Decision Tree

A clear incident to billing decision tree helps healthcare providers determine if services by non-physician practitioners (NPPs, like physician assistants, nurse practitioners) or auxiliary personnel can be billed under a supervising physician’s NPI at 100% of the Medicare Physician Fee Schedule (MPFS) rate.

Missteps might lead to coverage denials, audits, overpayment demands, or False Claims Act (FCA) allegations, but the devil is in the details.

For example, here are some of the details.  Simply stating that a health care provider failed to meet these guidelines is not enough, based on my experience as a medical billing expert witness.  Medical billing audits to determine compliance or non-compliance must be performed using a statistically valid method, including appropriate sample sizes, potentially a valid stratification strategy if applicable, and then, and only then could an expert extrapolate to describe or characterize all of the documentation and medical coding as compliant, non-compliant, or in the hands of retaining counsel, potentially false claims or fraud.

In other words, the decision tree below provides some insights into the “individual inquiries” that would be required to determine if the medical documentation supports this six-step criterion.

In disputes, a medical billing expert witness is invaluable. These specialists conduct forensic reviews of medical records, claims data, and documentation to opine on whether the provider met (or failed to meet) each of the six core criteria. Their testimony helps courts, regulators, and attorneys distinguish inadvertent errors from willful non-compliance, often influencing settlements, penalty reductions, or successful defenses in civil litigation.

To explain this another way, the decision tree is based on CMS guidelines, the CY 2026 PFS Final Rule (permanent virtual direct supervision), and established industry standards.^1,2,3

Incident-To Billing Decision Tree: Step-by-Step Medicare Compliance Check (2026 Rules)

Start: Service performed by NPP (e.g., PA, NP) or auxiliary personnel.

Step 1: Non-Facility Setting Requirement

For example, Is the service furnished in a non-facility setting? (e.g., physician office/clinic; not hospital outpatient/ED/institutional POS 19/22/23)^1,4

• No → No incident-to billing. Bill under NPP’s NPI (typically 85% MPFS) or use split/shared rules. End.
• Yes → Proceed.

Medical Billing Expert Witness Role: A medical billing expert witness reviews place-of-service codes and facility vs. non-facility designations to confirm eligibility and identify improper facility-setting claims.

Step 2: Established Patient Requirement

For example, Is the patient established with the practice/group? (Physician has performed initial evaluation, established diagnosis, and initiated a documented treatment/care plan; no new patient or new problem without physician evaluation)^1,5

• No → Bill under NPP’s NPI (85% rate). End.
• Yes → Proceed.

For example, Medical Billing Expert Witness Role: Experts examine initial E/M notes, problem lists, and care plans to determine if the patient was truly “established,” a common audit trigger for overbilling incident-to on new issues.

Step 3: Integral and Incidental to Physician Services

For example, Is the service integral and incidental to the physician’s professional services? (Follow-up care per physician-initiated plan, commonly included in the physician’s bill, not a separate Medicare benefit like standalone diagnostics)¹

• No → Bill under NPP’s NPI. End.
• Yes → Proceed.

Medical Billing Expert Witness Role: Medical billing expert witnesses analyze service descriptions, CPT codes, and plan adherence to assess whether the service was truly “incidental” or should have been billed separately/directly.

Step 4: Expense to the Practice Requirement

For example, Does the service represent an expense to the billing physician/practice? (NPP/auxiliary is employed, leased, or contracted by the practice under valid state law; not a free/external resource)¹

• No → No incident-to billing. End.
• Yes → Proceed.

Medical Billing Expert Witness Role: Experts review employment contracts, W-2s, lease agreements, and billing arrangements to verify the required financial/employment nexus.

Step 5: Supervision Requirement Met?

For example, Is the required level of supervision met? (Direct for most; general for TCM/CCM/behavioral health auxiliary)^1,2,3

• Direct Supervision (most services): Physician immediately available; 2026 permanent update allows virtual real-time audio/video (no audio-only), except global surgery 010/090 (in-person required).
• General Supervision (e.g., behavioral health low-risk): Oversight without presence.
• Yes → Proceed.
• No → Bill under NPP’s NPI. End.

Medical Billing Expert Witness Role: Medical billing expert witnesses scrutinize supervision logs, timestamps, virtual platform records, and physician presence to confirm compliance—often the most disputed element in audits.

Step 6: Physician Active Involvement in Treatment Course

Is the physician actively involved in the overall course of treatment? (Periodic evaluation/frequency based on patient needs; documented involvement)^1,5

• Yes → All six steps met → Bill incident-to under physician’s NPI at 100% MPFS rate. End.
• No → Reassess; likely bill under NPP. End.

For example, Medical Billing Expert Witness Role: Experts evaluate ongoing physician notes, frequency of involvement, and documentation to testify on active management—critical for defending against allegations of “rubber-stamping” NPP services.

Why Proper Documentation of the Six Steps Matters – And How a Medical Billing Expert Witness Helps

In summary, proper documentation across these six steps is essential to avoid audits by MACs (e.g., Noridian), OIG scrutiny, or DOJ/FCA cases. In other words, when disputes arise, engaging a qualified medical billing expert witness early provides objective analysis of records, calculates accurate overpayments (if any), opines on industry standards, and differentiates mistakes from fraud. To put it another way, expertise often strengthens audit responses, supports self-disclosures, mitigates penalties, or prevails in qui tam/FCA litigation.⁵

Key Takeaways for Incident-To Billing Compliance in 2026

• Update policies for permanent virtual direct supervision (audio/video only, exclusions apply).
• Behavioral health often allows general supervision + virtual options for better access.
• Always verify the latest MAC policies and CY 2026 PFS details.

For personalized guidance on incident-to billing compliance or expert witness needs, consult resources like the Medical Billing Expert Witness page.

Medicare Incident-To Billing Guidelines: 2015 vs 2026 Comparison

This table compares the key elements of the incident-to billing decision tree under Medicare rules in 2015 (pre-Public Health Emergency flexibilities) versus the permanent rules effective in 2026 (CY 2026 Physician Fee Schedule Final Rule, effective January 1, 2026). It includes specific emphasis on the behavioral health exception, where general supervision is permanently permitted for certain low-risk behavioral health auxiliary services (e.g., follow-up psychotherapy sessions).

Summary: The six core decision tree steps have remained largely consistent since 2015. Key 2026 advancements include permanent virtual direct supervision for most services and permanent general supervision for low-risk behavioral health auxiliary services (shift from direct supervision pre-PHE; flexibilities began temporarily in 2020 COVID waivers and were made permanent/enhanced in subsequent PFS rules, culminating in CY 2026 emphasis on access).

Always consult current CMS and MAC (e.g., Noridian) resources for the latest guidance, as policies may receive minor clarifications or updates

Here is a side by side comparison of the decision tree flows for 2015 and 2026:

Side-by-Side Comparison: Medicare Incident-To Billing Decision Trees
2015 (Pre-PHE) vs 2026 (Permanent Rules)

flowchart TD
    A[Start
Service by NPP or Auxiliary]:::start
    A --> B{1. Non-Facility Setting?
Office/clinic, home
NOT hospital/ED/SNF/POS 19/22/23}
    B -->|No| C[Cannot bill incident-to
Bill NPP NPI 85% MPFS
End]:::red
    B -->|Yes| D{2. Established Patient?
MD initial eval + plan
No new patient/problem w/o MD}
    D -->|No| E[Bill NPP NPI 85%
End]:::red
    D -->|Yes| F{3. Integral & Incidental?
Follow-up per MD plan
Not separate benefit}
    F -->|No| G[Bill NPP NPI 85%
End]:::red
    F -->|Yes| H{4. Expense to Practice?
Employed/leased/contracted}
    H -->|No| I[Cannot bill incident-to
End]:::red
    H -->|Yes| J{5. Supervision Met?}
    J --> K{Direct?
Audio/video virtual permanent
Except globals 010/090 in-person}
    J --> L{General?
TCM/CCM + certain BH auxiliary}
    J --> M{Permanent BH Exception?
Low-risk BH auxiliary
e.g. psychotherapy follow-up
General supervision only}
    K -->|Yes| SupYes
    K -->|No| SupNo
    L -->|Yes| SupYes
    L -->|No| SupNo
    M -->|Yes| SupYes
    M -->|No| K
    SupYes --> N{6. Physician Actively Involved?
Periodic eval, documented}
    SupNo --> O[Bill NPP NPI 85%
End]:::red
    N -->|No| P[Bill NPP NPI 85%
End]:::red
    N -->|Yes| Q[Bill Incident-To
Physician NPI 100% MPFS
End]:::green
    classDef start fill:#e6f3ff,stroke:#0066cc
    classDef green fill:#d4edda,stroke:#28a745
    classDef red fill:#f8d7da,stroke:#dc3545

flowchart TD
    A[Start
Service by NPP or Auxiliary]:::start
    A --> B{1. Non-Facility Setting?
Office/clinic, home
NOT hospital/ED/SNF/POS 19/22/23}
    B -->|No| C[Cannot bill incident-to
Bill NPP NPI 85% MPFS
End]:::red
    B -->|Yes| D{2. Established Patient?
MD initial eval + plan
No new patient/problem w/o MD}
    D -->|No| E[Bill NPP NPI 85%
End]:::red
    D -->|Yes| F{3. Integral & Incidental?
Follow-up per MD plan
Not separate benefit}
    F -->|No| G[Bill NPP NPI 85%
End]:::red
    F -->|Yes| H{4. Expense to Practice?
Employed/leased/contracted}
    H -->|No| I[Cannot bill incident-to
End]:::red
    H -->|Yes| J{5. Supervision Met?}
    J --> K{Direct?
In-person only
Physician present in suite & immediately available
No virtual}
    J --> L{General?
Limited only (e.g. some CCM/TCM)
BH: typically direct
No broad BH general exception}
    K -->|Yes| SupYes
    K -->|No| SupNo
    L -->|Yes| SupYes
    L -->|No| SupNo
    SupYes --> N{6. Physician Actively Involved?
Periodic eval, documented}
    SupNo --> O[Bill NPP NPI 85%
End]:::red
    N -->|No| P[Bill NPP NPI 85%
End]:::red
    N -->|Yes| Q[Bill Incident-To
Physician NPI 100% MPFS
End]:::green
    classDef start fill:#e6f3ff,stroke:#0066cc
    classDef green fill:#d4edda,stroke:#28a745
    classDef red fill:#f8d7da,stroke:#dc3545

Citations – Sources and Basis for these statements, related posts regarding medical billing expert opinions

1. Billing a PA’s Services Incident to a Physician’s – AAPC Knowledge Center, May 1, 2023.
2. Calendar Year (CY) 2026 Medicare Physician Fee Schedule Final Rule (CMS-1832-F) – CMS, October 31, 2025.
3. Medicare Physician Fee Schedule Final Rule Summary: CY 2026 (MM14315) – CMS, December 5, 2025.
4. Noridian Medicare, “Incident to Services” – Accessed January 2026.
5. Your article: Understanding Incident to Billing in Medicare: Key Compliance Guidelines, Audit Risks, and the Vital Role of Medical Billing Expert Witnesses – No World Borders, January 2026.