Modifier 33: Preventive Services Explained (Coding Guide 2026)

Last Updated: February 2026 | Verified for 2026 AMA, CPT & CMS Guidelines

Quick Reference

• Definition: Identifies that the primary purpose of a service is the delivery of an evidence-based preventive service under ACA mandates, USPSTF A or B recommendations, ACIP immunization guidelines, or HRSA-supported preventive care guidelines — signaling to payers that zero patient cost-sharing applies.

• Payer Applicability: Commercial/private payers only. Do NOT submit to Medicare or Medicaid — Medicare uses dedicated HCPCS G codes and does not recognize modifier 33 for most services (with limited exceptions for anesthesia with screening colonoscopy and Advance Care Planning with AWV).

• ACA Authority: Created in response to the Patient Protection and Affordable Care Act (PPACA), Section 2713, which mandates first-dollar coverage of qualifying preventive services by non-grandfathered health plans.

• Do NOT use when: The CPT or HCPCS code is already specifically identified as a preventive/screening service in its descriptor (e.g., G0202 for screening mammography, routine well-child codes). The modifier is redundant and may cause claim errors.

• Colonoscopy Conversion Rule: When a screening colonoscopy becomes therapeutic (e.g., polyp removal), append modifier 33 to the therapeutic CPT code for commercial payers. For Medicare, use modifier PT instead.

• 2026 Update: The AMA made an editorial revision to the modifier 33 descriptor in the 2026 CPT code set. No substantive change to the clinical application; confirm the exact revised language in the CPT 2026 Professional Edition or with your MAC.

CPT Modifier 33 — Preventive Services is one of the most misunderstood and frequently misapplied modifiers in medical billing. Created in 2010 as a direct response to the Affordable Care Act (ACA), it serves a critically important function: it signals to commercial health plans that a service qualifies as a mandated preventive benefit under federal law, thereby eliminating patient cost-sharing — deductibles, copays, and coinsurance — entirely. When applied correctly, modifier 33 protects patients from surprise bills and ensures practices receive full reimbursement for covered preventive services. When applied incorrectly — or omitted when required — it results in denied claims, patient billing errors, compliance risk, and audit exposure.

Definition, ACA Authority & Legislative Background

The official CPT definition of Modifier 33 is: “When the primary purpose of the service is the delivery of an evidence-based service in accordance with a US Preventive Services Task Force A or B rating in effect and other preventive services identified in preventive services mandates (legislative or regulatory), the service may be identified by adding 33 to the procedure. For separately reported services specifically identified as preventive, the modifier should not be used.”

Modifier 33 was introduced in late 2010 but, because it was published after the 2011 CPT code book had already gone to press, it did not appear in that edition — causing widespread confusion in its early years. It was specifically created in response to Section 2713 of the Public Health Service Act (PHSA), added by the Affordable Care Act, which requires that non-grandfathered group health plans and individual health insurance policies cover certain preventive services with no cost-sharing to the patient when provided by an in-network provider.

The modifier exists because many preventive services do not have unique CPT or HCPCS codes that identify them as preventive. For example, a lipid panel (CPT 80061) is used for both diagnostic workups and as a preventive cholesterol screening.

Without modifier 33, the commercial payer may process the claim under the patient’s diagnostic benefit — applying deductibles and coinsurance. By appending -33, the provider signals that this is a qualifying preventive service and zero patient cost-sharing should apply.

Key Principle — “Primary Purpose” Rule: Modifier 33 is only appropriate when the primary purpose of the service is prevention. If the lipid panel was ordered to monitor a patient already on statins for known hyperlipidemia, the purpose is diagnostic monitoring — not preventive screening — and modifier 33 does not apply. Always assess clinical intent before appending this modifier.

The Four ACA Preventive Service Categories

To correctly apply modifier 33, the service must fall within one of the four categories of preventive services defined by federal law and designated by the four ACA-mandated organizations:

Practical Step: Before every preventive encounter, verify the patient’s eligibility for zero-dollar cost-sharing by checking the relevant organization’s recommendations (USPSTF, CDC ACIP schedules) against the patient’s age, sex, and risk category. Not every patient qualifies for every service at zero cost-sharing — only those who fall within the specific population the recommendation targets.

When to Use Modifier 33: Rules & Decision Framework

flowchart TD
    A[Service ordered] --> B{Commercial or Medicare payer?}
    B -->|Medicare| C{Is it anesthesia with screening colonoscopy<br>OR ACP with AWV?}
    C -->|Yes| D[Append Modifier 33]
    C -->|No| E[Do NOT use Modifier 33<br>Use G codes or Modifier PT]
    B -->|Commercial| F{Is the service an ACA-qualifying<br>preventive service?<br>USPSTF A/B, ACIP, HRSA}
    F -->|No| G[Do NOT use Modifier 33]
    F -->|Yes| H{Is the CPT code already<br>inherently identified as preventive<br>in its descriptor?}
    H -->|Yes| I[Modifier 33 generally not needed<br>but adding it is the safer choice]
    H -->|No| J[Append Modifier 33<br>to waive patient cost-sharing]

Use modifier 33 when all three of the following conditions are met:

• Condition 1 — Commercial Payer: The claim is being submitted to a private/commercial insurance carrier, not Medicare or Medicaid (with the narrow Medicare exceptions described in Section 5).

• Condition 2 — Qualifying Service: The procedure is an evidence-based preventive service within one of the four ACA categories above (USPSTF A/B, ACIP, HRSA pediatric, HRSA women’s).

• Condition 3 — Not Inherently Preventive: The CPT code used is not already inherently and exclusively identified as a preventive service in its descriptor. Services like annual well-child exams (99381–99385 for new patients, 99391–99395 for established) and routine screening mammography (77067) are understood as preventive by most payers and may not require modifier 33. However, when in doubt, adding the modifier is the safer choice for non-Medicare claims.

Common services that typically require modifier 33 for commercial claims:

• Lipid panel (80061) ordered as preventive cholesterol screening per USPSTF

• Blood glucose/HbA1c ordered as diabetes screening (not management)

• Depression screening instruments (PHQ-9 administered during a preventive visit, reported separately)

• Tobacco cessation counseling (99406, 99407) — not always inherently treated as preventive

• Aspirin counseling and chemoprevention counseling services

• Colonoscopy CPT codes (45378, 45380, 45385, etc.) when performed as cancer screening

• BRCA counseling (96040) for appropriate high-risk women

• Low-dose CT for lung cancer screening (71250 with modifier 33)

• Abdominal aortic aneurysm ultrasound (76706) for qualifying male smokers

When NOT to Use Modifier 33: Common Billing Mistakes

Do NOT append modifier 33 in these situations:

• Medicare or Medicaid claims (general rule): Medicare uses dedicated HCPCS G codes (G0105, G0121, G0202, etc.) that already identify services as preventive. Submitting modifier 33 to Medicare will result in claim rejection with MOA code MA130 (incomplete/missing information). Medicare does not recognize this modifier for most services.

• Services already identified as preventive by their CPT/HCPCS descriptor: If the code itself says “screening” (e.g., G0103 prostate cancer screening PSA, G0389 abdominal aortic aneurysm screening), do not add 33 — per CPT Appendix A instructions, the modifier should not be used for “separately reported services specifically identified as preventive.”

• HCPCS Level II G codes: Never combine modifier 33 with G codes. HCPCS preventive service codes and modifier 33 serve overlapping purposes and should not be stacked on the same claim line.

• Diagnostic services ordered for existing conditions: A lipid panel ordered to monitor a patient already on statin therapy for diagnosed hyperlipidemia is a diagnostic service, not preventive screening. The primary purpose fails the test.

• Services with USPSTF Grade C, D, or I recommendations: Only A and B grades qualify. Grade C recommendations may have conditional coverage depending on payer policy; Grade D means the USPSTF recommends against the service.

• Out-of-network providers: The ACA zero-cost-sharing mandate only applies to in-network providers under most plan structures. Patients seen out-of-network may still owe cost-sharing regardless of modifier 33.

• Grandfathered health plans: Health plans that existed before March 23, 2010, and have not made significant benefit changes, are exempt from the ACA preventive services mandate. Modifier 33 does not override this exemption.

• Modifier 33 + Modifier PT on the same claim line: Never stack these together. They are mutually exclusive. Use PT for Medicare; use 33 for commercial claims.

Medicare vs. Commercial Payer Rules (Modifier 33 vs. PT)

This is the area that generates the most billing errors and audits. The table below clarifies the critical payer-specific rules:

The Two Medicare Exceptions Where Modifier 33 IS Accepted:

1. Anesthesia with Screening Colonoscopy (since 2015): When moderate sedation or anesthesia is provided in conjunction with a Medicare-covered screening colonoscopy (G0105 or G0121), modifier 33 may be appended to the anesthesia code (e.g., 00812-33) to ensure the anesthesia is also processed at zero patient cost-sharing. This was clarified by CMS guidance in 2015.

2. Advance Care Planning with Annual Wellness Visit (since 2016): When CPT codes 99497 or 99498 (Advance Care Planning) are furnished as an optional element of a Medicare Annual Wellness Visit (G0438 or G0439) on the same date, append modifier 33 to 99497/99498. This waives the coinsurance and deductible for the ACP service. Do NOT add modifier 33 to 99497/99498 if it is billed on a different date or without a payable AWV.

Colonoscopy Conversion: The Most Common and Complex Use Case

The colonoscopy-to-polypectomy conversion scenario is the most frequently cited and audited application of modifier 33. Understanding it thoroughly is essential for gastroenterology, general surgery, and colorectal surgery practices.

The Core Rule: A colonoscopy is defined as a “screening” by the intent at the time of scheduling — the patient was asymptomatic and the procedure was ordered for population-based cancer prevention. When the physician encounters a polyp or lesion during that screening and performs a therapeutic intervention (biopsy, polypectomy, ablation), the procedure code changes — but the intent remains preventive.

Modifier 33 (commercial) or PT (Medicare) preserves that preventive intent so cost-sharing is not incorrectly applied. Step-by-Step Coding Workflow for Commercial Payers:

Critical Rule — Diagnosis Sequencing: When a screening colonoscopy converts to therapeutic, always list the screening diagnosis (Z12.11) as primary and the finding (polyp, lesion) as secondary.

This sequence reinforces the preventive intent of the encounter and supports the application of modifier 33. Reversing the order — listing the polyp as primary — signals a diagnostic/therapeutic encounter and may result in the payer applying cost-sharing.

Anesthesia Coding for Colonoscopy: When a screening colonoscopy remains diagnostic only, use anesthesia code 00812. When the procedure converts to therapeutic (e.g., polypectomy), the anesthesia code changes to 00811 with modifier PT (Medicare) or 33 (commercial). Using 00812 after a polypectomy is a common audit trigger flagged by the OIG and CMS.

Same-Day Billing: Preventive + E/M, Modifier 33 + Modifier 25

A common and frequently misunderstood scenario: a patient presents for a preventive/wellness visit and also has a new acute problem or chronic issue that requires separate evaluation and management. The Rule: You may bill both the preventive medicine service and a separate E/M code on the same day — but the problem-oriented E/M must be significant, separately identifiable from the preventive service.

Append Modifier 25 to the E/M code, not to the preventive code. Do not add modifier 33 to the E/M code — the E/M is a problem-focused service, not a preventive service.

Example: A 50-year-old woman presents for her annual well-woman visit. During the visit, she reports new-onset knee pain that requires separate evaluation. The physician performs the annual exam (including Pap, mammography referral, USPSTF counseling) and also conducts an expanded problem-focused exam of the knee with a separate plan.

• Bill: 99395 (preventive medicine, established patient, 40–64) — no modifier 33 needed; this code is inherently preventive.

• Bill: 99213-25 (E/M, established patient, low complexity) — modifier 25 signals a significant, separate E/M on the same date.

If the preventive service itself requires modifier 33 (e.g., a preventive lipid panel ordered during the visit), append 33 to that specific procedure code (e.g., 80061-33), not to the office visit code.

Patient Communication is Essential: When billing both a preventive service and a problem-focused E/M on the same day, the patient may owe a copay/deductible for the E/M portion but NOT for the preventive component. Patients often receive unexpected bills when this happens. Educate patients proactively with an advance notice explaining that two services are being billed — one covered at 100% (preventive) and one subject to their standard plan benefits (the E/M).

Advance Care Planning (99497/99498) with Annual Wellness Visit

This is one of the two scenarios where Medicare does accept modifier 33. When a physician provides Advance Care Planning services (CPT 99497 — first 30 minutes; 99498 — each additional 30 minutes) as a voluntary, patient-requested component of a Medicare Annual Wellness Visit on the same date of service, modifier 33 must be appended to the ACP code to waive the applicable coinsurance and deductible for the Medicare beneficiary.

Requirements for Medicare ACP + AWV with Modifier 33:

• The AWV (G0438 or G0439) must be billed on the same claim and same date of service.

• The AWV must be a payable AWV (i.e., the patient is eligible — typically one per year).

• ACP must be patient-initiated/voluntary, not provider-mandated.

• Do NOT append modifier 33 to G0136 (SDOH risk assessment) in this context unless billed with a payable AWV on the same date per Noridian and other MAC guidance.

• Billing: 99497-33 (and G0438 or G0439) on the same claim.

Immunizations & Modifier 33

Routine immunizations recommended by the CDC’s ACIP schedules are covered ACA preventive services for both children and adults. For most commercial payers, immunization administration codes (90460–90461 for physician counseling; 90471–90474 for non-counseling administration) billed alongside the vaccine product codes do not require modifier 33 because payers already classify them as preventive services from the code context alone. However, in cases where a payer is applying cost-sharing to an ACIP-recommended vaccine, modifier 33 may be appended to both the administration code and the vaccine product code to reinforce the preventive coverage mandate. Always verify payer-specific guidance first.

Vaccines typically NOT requiring modifier 33 (payers already recognize them as preventive): influenza (90686–90689), HPV (90651, 90650), pneumococcal (90670, 90732), Shingrix (90750), MMR (90707), varicella (90716), Tdap (90715). Excluded vaccines (not covered by ACA): Travel vaccines (typhoid, yellow fever, Japanese encephalitis, rabies) and occupational vaccines (anthrax, BCG for TB) are not ACIP routine schedule vaccines and do not qualify for zero cost-sharing under the ACA preventive mandate.

Documentation & Audit-Proof Compliance Standards

Modifier 33 itself does not require extensive additional documentation beyond what is needed to support the preventive nature of the service — but your chart and claim must be internally consistent and must support the clinical intent. Auditors from the OIG, Recovery Audit Contractors (RACs), and commercial payer Special Investigations Units (SIUs) specifically look at modifier 33 claims when:

• The same service is billed as both preventive (modifier 33) and diagnostic for different patients in the same encounter pattern.

• Modifier 33 is appended to HCPCS G codes (which is incorrect and a clear error).

• Colonoscopy claims show modifier 33 on Medicare claims where PT should be used instead.

• The diagnosis code does not support preventive intent (e.g., 80061 billed with 33 but the ICD-10 code is E78.5 — mixed hyperlipidemia — a diagnostic code, not a screening code).

Best-Practice Documentation Elements:

• Preventive Intent Statement: In the procedure note or visit documentation, clearly state the screening/preventive intent. Example: “Patient is a 48-year-old male with no prior colorectal cancer symptoms presenting for routine colorectal cancer screening per USPSTF guidelines. Screening colonoscopy performed.” This language directly supports modifier 33.

• Diagnosis Code Alignment: Always use Z-codes (ICD-10 encounter for screening codes) as the primary diagnosis when the service is purely preventive. Example: Z12.11 (encounter for screening for malignant neoplasm of colon), Z13.89 (encounter for screening for other disorders), Z00.00 (encounter for general adult medical examination).

• Patient Eligibility Notation: For USPSTF-recommended services, note the patient meets eligibility criteria (e.g., “Patient is age 45, asymptomatic, meets USPSTF criteria for CRC screening”).

• Conversion Documentation (Colonoscopy): When a screening converts to therapeutic, document the finding and intervention clearly. Example: “Screening colonoscopy initiated; 8mm sessile polyp identified in sigmoid colon and removed by snare polypectomy. Procedure initially scheduled as and constitutes a preventive colorectal cancer screening.”

• Payer Eligibility Verification: Keep a record (in the practice management system or EHR) that the patient’s plan was confirmed as a non-grandfathered commercial plan prior to billing modifier 33. This protects you in an audit.

Denial Management & Corrected Claims

If a claim is denied because modifier 33 was omitted or applied incorrectly, the pathway to correction is straightforward but time-sensitive:

• Omitted modifier 33 (commercial payer): Submit a corrected claim (CMS-1500, Box 19 — Billing Note: “Corrected claim — Modifier 33 omitted on original submission. Service is a qualifying ACA preventive service under USPSTF [grade]. Zero patient cost-sharing applies.”) Include documentation supporting preventive intent. Most plans allow corrected claim submissions within 90–180 days of the original claim date, per contract terms.

• Incorrectly applied modifier 33 to Medicare: Submit a corrected claim removing the modifier. Be aware that if the patient was incorrectly billed zero for a service that should have had Medicare cost-sharing, you may need to issue a patient statement for the applicable deductible/coinsurance.

• Modifier 33 + PT on same line: Void and resubmit with only the appropriate modifier for the payer type.

• Wrong diagnosis code: Submit a corrected claim with the corrected Z-code as primary diagnosis, supporting the preventive nature of the service.

Audit Risk Alert: A 2022 OIG review of outpatient colonoscopy claims found that up to 18% of denied colonoscopy claims were linked to missing or incorrect modifiers — most commonly when a screening procedure converted to a therapeutic procedure mid-procedure and the modifier was omitted. Commercial payer SIU auditors specifically flag colonoscopy, mammography, and lipid screening claims for modifier 33 compliance.

Complex Clinical Coding Scenarios

Scenario 1: Screening Colonoscopy Converts to Polypectomy (Commercial Payer)

Patient: 52-year-old woman with commercial insurance (non-grandfathered plan). No symptoms. No personal or family history of CRC. Presents for routine colonoscopy screening. Finding: Two 6mm polyps found in the descending colon; removed by snare polypectomy. Coding:

• CPT 45385-33 (Colonoscopy with removal of polyp by snare technique + Modifier 33)

• Diagnosis: Z12.11 primary (encounter for CRC screening); K63.5 secondary (polyp of colon)

Rationale: The procedure was initiated as a preventive service. Modifier 33 on the therapeutic code preserves the preventive intent and ensures zero patient cost-sharing. Do NOT use G0121 — that is a Medicare code. Do NOT use modifier PT — that is for Medicare only.

Scenario 2: Preventive Lipid Screening at Annual Physical (Commercial)

Patient: 42-year-old male, no known cardiovascular disease, no prior lipid panel, presents for annual physical. Physician orders lipid panel per USPSTF B recommendation (dyslipidemia screening for adults without lipid disorder). Coding:

• CPT 99395 (Preventive medicine visit, established patient, 40–64) — no modifier 33 needed; inherently preventive.

• CPT 80061-33 (Lipid panel + Modifier 33) — needed because 80061 is not exclusively a preventive code.

Diagnosis for 80061-33: Z13.220 (encounter for screening for lipoid disorder) Rationale: Without modifier 33, the commercial payer may process the lipid panel under the patient’s diagnostic lab benefit and apply a deductible. With -33, it is covered at 100%.

Scenario 3: Preventive Visit + Separate E/M for Acute Problem (Same Day)

Patient: 35-year-old woman with commercial insurance presents for annual well-woman exam. During the visit, she reports a 3-week history of right ear pain and decreased hearing. Physician performs the preventive exam AND conducts a separate, problem-focused evaluation of otitis media, prescribing antibiotics.

Coding:

• CPT 99385 (Preventive medicine, new patient, 18–39) — no modifier 33.

• CPT 99213-25 (Office visit, established, low complexity + Modifier 25 for significant, separate E/M).

Note: Modifier 33 does NOT go on the E/M code. The E/M is a diagnostic/therapeutic service, not preventive. Patient will owe a copay for the 99213 but not for the 99385.

Scenario 4: Advance Care Planning with Medicare Annual Wellness Visit

Patient: 74-year-old Medicare patient. Has her annual wellness visit (AWV). During the AWV, at her request, the physician spends 35 minutes discussing advance directives and completing a POLST form.

Coding:

• HCPCS G0439 (Subsequent Annual Wellness Visit)

• CPT 99497-33 (Advance Care Planning, first 30 minutes + Modifier 33)

Rationale: Modifier 33 on 99497 is one of the two Medicare-accepted uses of the modifier. It waives the coinsurance and deductible for the ACP service. If billed on a separate date without G0439, do not use modifier 33.

Scenario 5: Low-Dose CT Lung Cancer Screening (USPSTF A Recommendation)

Patient: 58-year-old current smoker (30 pack-year history) with commercial insurance. Physician refers for low-dose CT (LDCT) for lung cancer screening per USPSTF A-grade recommendation (adults age 50–80, ≥20 pack-year history, current or recent ex-smoker).

Coding (radiologist billing):

• CPT 71250-33 (CT thorax without contrast + Modifier 33)

• Diagnosis: Z12.31 (encounter for screening for malignant neoplasm of lung)

Note: For Medicare, use G0297 (LDCT for lung cancer screening) — do not append modifier 33 to the Medicare claim.

Modifier 33 vs. PT vs. KX: Side-by-Side Comparison