Modifier 33 and Modifier PT: Deciding When a Service Is Preventive

Modifier 33 says a service was preventive. Modifier PT says a colorectal cancer screening became something else. They point in opposite directions, they belong to different rule systems, and contractor guidance says plainly that they should not be submitted on the same claim line.

What both are really doing is moving cost-sharing. Neither changes what is paid to the practice; both change whether the patient owes a deductible or coinsurance. That makes this one of the few modifier decisions where getting it wrong produces a patient complaint before it produces a denial — and where getting it right requires answering a question most coders are not asked to answer: is this service preventive under the rules that govern this particular patient’s coverage?

The Decision Rule

Modifier 33 — the primary-purpose test

Modifier 33 is used where the primary purpose of the service is the delivery of an evidence-based service that has an A or B rating in effect from the United States Preventive Services Task Force, or is one of the other preventive services identified in legislative or regulatory preventive services mandates. Where a service is already specifically identified as preventive in its own code description, the modifier is not used — the code has already said it.

That definition is not free-floating. It tracks 45 CFR 147.130, the regulation implementing section 2713 of the Public Health Service Act, which requires a group health plan or issuer to cover, without any cost-sharing, four categories of service:

• evidence-based items or services with an A or B rating in the current USPSTF recommendations with respect to the individual involved;
• immunizations for routine use with a recommendation in effect from the CDC’s Advisory Committee on Immunization Practices — in effect once adopted by the CDC Director, and "for routine use" if listed on the CDC immunization schedules;
• for infants, children and adolescents, evidence-informed preventive care and screenings in the comprehensive guidelines supported by the Health Resources and Services Administration; and
• for women, additional preventive care and screenings in the HRSA-supported comprehensive guidelines, subject to the contraceptive-coverage exemption and accommodation provisions at 45 CFR 147.131 to 147.133.

A fifth category covers qualifying coronavirus preventive services — a USPSTF A or B item or an ACIP-recommended immunisation, the latter regardless of whether it is recommended for routine use.

The office-visit rule that modifier 33 actually implements

The regulation does not stop at listing services. Paragraph (a)(2) sets out exactly when the visit is also free of cost-sharing, and this is the test modifier 33’s "primary purpose" language mirrors:

1. If the preventive item or service is billed separately from the office visit, the plan may impose cost-sharing on the office visit.
2. If it is not billed separately and the primary purpose of the visit was to deliver it, the plan may not impose cost-sharing on the visit.
3. If it is not billed separately and the primary purpose of the visit was not to deliver it, the plan may impose cost-sharing on the visit.

The regulation illustrates with four worked examples. A cholesterol screening billed separately alongside an office visit: no cost-sharing on the lab work, cost-sharing permitted on the visit. A blood pressure screening taken during a visit for recurring abdominal pain, with only an office visit billed: cost-sharing permitted, because the primary purpose was not preventive. A child’s annual physical under the HRSA guidelines, billed as an office visit with some additional non-guideline items: no cost-sharing, because the primary purpose was the guideline service.

That third example is the one to memorise. A preventive service happening during a visit does not make the visit preventive. Modifier 33 asserts primary purpose, and a note that documents a problem-focused encounter with an incidental screening does not support it.

Modifier PT — the Medicare conversion modifier

Modifier PT is a Medicare HCPCS modifier reporting that a colorectal cancer screening test became a diagnostic or therapeutic service. It is the modifier for the classic case: the patient arrives for a screening colonoscopy, a polyp is found, and the procedure is now something the screening code does not describe.

Chapter 18 of the Medicare Claims Processing Manual (Publication 100-04), Section 60.1.1, sets out what PT does to the patient’s bill, and the answer has been moving on a statutory schedule. Section 122 of Division CC of the Consolidated Appropriations Act, 2021 amended section 1833(a) of the Social Security Act to create a special coinsurance rule for screening flexible sigmoidoscopies and screening colonoscopies — regardless of the code billed for establishing a diagnosis as a result of the test, or for removing tissue or other matter, furnished in connection with, as a result of, and in the same clinical encounter as the screening test. The coinsurance is being phased out:

Dates of service	Deductible	Coinsurance
CY 2023 through CY 2026	Waived	Reduced to 15 percent
CY 2027 through CY 2029	Waived	Reduced to 10 percent
On or after 1 January 2030	Waived	Waived entirely

Two mechanics in that instruction matter operationally. First, the trigger is modifier PT appended to at least one code on the claim indicating that G0104, G0105 or G0121 became a diagnostic or therapeutic service. Second, the reduced coinsurance then applies to all procedure codes that meet the requirements and are performed on that date of service and billed on the same claim. Splitting the encounter across two claims puts the second one outside the rule.

Where modifier PT goes on the claim

Contractor guidance is more operational than the manual here. Modifier PT is appended to the diagnostic procedure code that is reported instead of the screening colonoscopy or screening sigmoidoscopy code — not added alongside the screening code. It is appended to surgical procedure codes in the range 10000 to 69999 and to G0500, and to the appropriately coded anesthesia procedure associated with one of those surgical codes. And the boundary condition: do not use modifier PT where the service began as a diagnostic procedure. A colonoscopy booked as diagnostic never converts, because it never started as a screening.

The same guidance states the deductible position broadly: Medicare waives the Part B deductible for all surgical procedures furnished on the same date and in the same encounter as a colonoscopy, flexible sigmoidoscopy or barium enema that was initiated as a colorectal cancer screening service and submitted with modifier PT.

Before 1 January 2022, when a screening colonoscopy became diagnostic, the beneficiary was liable for the full applicable coinsurance. Old advice on this point is not merely outdated; it is now wrong by a large margin.

33 vs PT: The Differentiation

	Modifier 33	Modifier PT
Type	CPT modifier	HCPCS Level II, Medicare
Says	This service was preventive	This colorectal screening became diagnostic or therapeutic
Rule system	PHS Act section 2713 / 45 CFR 147.130 — commercial and ACA-regulated coverage	Medicare cost-sharing under section 1833 of the Social Security Act
Effect	Cost-sharing not imposed on a qualifying preventive service or visit	Deductible waived; coinsurance reduced on the statutory schedule above
Scope	Any USPSTF A/B or mandated preventive service	Colorectal cancer screening only
Together	Not on the same claim line. They make contradictory assertions about the same service.

Medicare recognises modifier 33 — but narrowly

Medicare’s preventive cost-sharing waiver does not come from 45 CFR 147.130. It comes from the statute: section 4104(b)(4) of the Affordable Care Act amended section 1833(a)(1) of the Social Security Act to require 100 percent payment for the initial preventive physical examination, the annual wellness visit, and preventive services recommended by the USPSTF with a grade of A or B for any indication or population and appropriate for the individual; section 4104(b) amended section 1833(b)(1) to waive the deductible on the same basis, effective 1 January 2011. Chapter 18, Section 1.3 records all of it — and adds a caution worth quoting: not all preventive services allowed in Medicare and recommended by the USPSTF carry a grade of A or B, so some Medicare preventive services do not qualify for the waiver at all.

Because Medicare’s waivers are already attached to the codes, modifier 33 has little work to do on a Medicare claim, and contractor guidance names the situations where it does. Add modifier 33 to waive the patient’s deductible and coinsurance on:

• advance care planning (99497 and its add-on) performed on the same day as an annual wellness visit;
• the social determinants of health risk assessment (G0136) performed on the same day as an annual wellness visit;
• moderate sedation (G0500 or 99153) furnished in conjunction with and in support of a screening colonoscopy (G0105 or G0121).

The pattern is consistent: these are codes that are not inherently preventive, being furnished on this occasion as part of a preventive encounter. That is exactly the gap modifier 33 was designed for.

The moderate-sedation case shows the handover precisely

Chapter 18, Section 60.1.1 traces one service across the boundary in two sentences. Coinsurance and deductible are waived for moderate sedation (G0500 or 99153) furnished in support of a screening colonoscopy when reported with modifier 33. When the screening colonoscopy becomes a diagnostic colonoscopy, moderate sedation is reported with only modifier PT — and only the deductible is waived.

The anesthesia codes behave the same way: anesthesia furnished in conjunction with and in support of a screening colonoscopy is reported with 00812, coinsurance and deductible waived; when the screening becomes diagnostic, anesthesia is reported with 00811 and modifier PT, and the deductible is waived.

So the same clinical event — a polyp found mid-procedure — changes the anesthesia code, changes the sedation modifier, and changes what the patient owes, without changing anything about the sedation itself.

A third modifier joins the colonoscopy decision

From 1 January 2023, colorectal cancer screening tests include a screening colonoscopy (G0105 or G0121) that follows a non-invasive stool-based test (82270, G0328 or 81528). The furnishing practitioner identifies that scenario by including the KX modifier on the screening colonoscopy claim, and neither deductible nor coinsurance applies to either test, because both are specified preventive screening services. This is a rare case of KX carrying a benefit-category meaning rather than a threshold attestation, and it is easy to miss.

What the Record Must Show

• The purpose of the encounter, stated at the top. Modifier 33 is a claim about primary purpose. The note should open by establishing that the visit was for the preventive service, not close by mentioning that one happened. Where a problem was also addressed, that is a modifier 25 question on a separate line, not a reason to drop modifier 33.
• Which recommendation the service rests on. USPSTF grade A or B, an ACIP recommendation, or a named HRSA guideline. The grade is what makes the cost-sharing waiver apply, and a service whose recommendation has changed grade is a different claim.
• For a converted colonoscopy: the sequence. The indication was screening; a lesion was found; tissue was removed or a diagnosis established in the same clinical encounter. The statutory rule is written around that sequence, and the record has to show the encounter began as a screening. A colonoscopy scheduled as diagnostic from the outset is not a converted screening and never carries PT.
• The claim as a unit. Because the reduced coinsurance applies to all qualifying codes performed that day and billed on the same claim, the billing decision about how to split the encounter is a patient-liability decision. Document the encounter as one.

The Misuse That Triggers Denials and Complaints

1. Modifier 33 on a code that is already preventive. Both the CPT convention and contractor guidance rule it out: do not add modifier 33 to any procedure code specifically identified as preventive in its own description. It is redundant at best and, where a payer edits on it, a denial.
2. Modifier 33 and modifier PT on the same claim line. Contractor guidance says not to. They assert opposite things.
3. Modifier 33 on a problem-oriented visit that happened to include a screening. The regulation’s own example forecloses it — a blood pressure screening during a visit for abdominal pain leaves the visit subject to cost-sharing.
4. Modifier 33 on advance care planning or the SDOH risk assessment billed on a different date from the wellness visit. Contractor guidance is explicit: the modifier is not added to G0136, 99497 or 99498 unless billed on the same claim and date of service as a payable initial or subsequent annual wellness visit.
5. Assuming a converted screening now costs the Medicare patient nothing. It does not, yet. Through CY 2026 the coinsurance is reduced to 15 percent, not eliminated. Quoting a patient zero is a complaint waiting to happen; so is quoting them the pre-2022 full coinsurance.
6. Splitting the encounter across claims. The reduced coinsurance applies to qualifying codes billed on the same claim. A separate claim for the pathology-driving procedure can fall outside it.
7. Using modifier 33 to make a non-covered service covered. It does neither. It is a cost-sharing modifier. A service outside the benefit is outside the benefit, and the question becomes one for the GX, GY and GZ liability set instead.

Where Jurisdiction Matters, and Where Guidance Diverges

The recommendations move, and the coverage obligation lags them deliberately. 45 CFR 147.130(b)(1) requires coverage for plan years beginning on or after the later of 23 September 2010 or one year after the date the recommendation or guideline is issued. So a new USPSTF A or B rating does not create an obligation immediately. And under paragraph (b)(2), a plan already covering an item on the first day of a plan year must continue to cover it through the last day of that plan or policy year even if the recommendation changes or is withdrawn mid-year. The result is that two patients with the same service on the same date can have different cost-sharing depending on when their plan years began.

Plans may still manage the service. Paragraph (a)(4) preserves reasonable medical management techniques to determine frequency, method, treatment or setting to the extent the recommendation does not specify them. A denial for frequency is not necessarily a denial of the preventive status.

Out-of-network is a real limit. Under paragraph (a)(3), a plan with a network is generally not required to cover a preventive service delivered out of network without cost-sharing — unless it has no in-network provider who can furnish it, in which case it must cover it without cost-sharing.

The polypectomy question under commercial coverage. The regulation itself, at paragraph (a)(5), permits a plan to impose cost-sharing for a treatment not described in paragraph (a)(1) even if the treatment results from an item or service that is described. How that principle applies to removing a polyp during a screening colonoscopy has been addressed in tri-agency sub-regulatory FAQ guidance rather than in the regulation. This guide does not state the FAQ position, because it could not be verified against a primary source at the time of writing — check the current tri-agency FAQs on Affordable Care Act implementation directly before advising a commercially insured patient. The Medicare answer, by contrast, is in the manual and in the statute, and is set out above.

MAC and payer variation. Noridian, Novitas and First Coast Service Options all publish preventive-services guidance and do not read identically on which situations warrant modifier 33. Commercial and Medicare Advantage plans set their own edits; several require modifier 33 in situations Medicare would not, and several ignore it entirely because their systems key off the code and diagnosis. Verify against the plan.

Frequently Asked Questions

What is modifier 33 used for?

To identify a service whose primary purpose was the delivery of a preventive service — one with a USPSTF A or B rating in effect, or one identified in a legislative or regulatory preventive services mandate — so that the patient’s cost-sharing is not applied. It is not used where the code itself already describes the service as preventive.

What is the difference between modifier 33 and modifier PT?

Modifier 33 says the service was preventive. Modifier PT says a colorectal cancer screening became a diagnostic or therapeutic service. Modifier 33 is a CPT modifier operating primarily under the ACA preventive-services rules at 45 CFR 147.130; PT is a Medicare HCPCS modifier operating under the Medicare cost-sharing rules. Contractor guidance says they should not be submitted on the same claim line.

What happens when a screening colonoscopy becomes diagnostic under Medicare?

Report the diagnostic or therapeutic code with modifier PT. The deductible is waived, and coinsurance is reduced under the schedule set by section 122 of Division CC of the Consolidated Appropriations Act, 2021: 15 percent for dates of service in CY 2023 through CY 2026, 10 percent for CY 2027 through CY 2029, and fully waived from 1 January 2030. Before 1 January 2022 the beneficiary was liable for the full coinsurance.

Does modifier PT go on every line of the claim?

The manual’s trigger is modifier PT appended to at least one code on the claim indicating that G0104, G0105 or G0121 became diagnostic or therapeutic. The reduced coinsurance then applies to all procedure codes meeting the requirements that were performed on that date of service and billed on the same claim.

Do I use modifier 33 on Medicare claims?

Rarely, and in specific situations. Contractor guidance names advance care planning and the social determinants of health risk assessment when performed on the same day as an annual wellness visit, and moderate sedation furnished in support of a screening colonoscopy. Medicare’s preventive cost-sharing waivers otherwise attach to the codes themselves under section 1833 of the Social Security Act.

Does a USPSTF grade C or D service qualify?

No. The cost-sharing rules key off an A or B rating. Chapter 18 notes explicitly that not all preventive services allowed in Medicare and recommended by the USPSTF carry a grade of A or B, and those that do not fall outside the waiver.

If a preventive screening happens during a problem visit, is the visit preventive?

Not by itself. The regulation’s test is primary purpose. Where the preventive item is billed separately, the plan may impose cost-sharing on the visit; where it is not billed separately and the visit’s primary purpose was not preventive, the plan may impose cost-sharing on the visit.

What does the KX modifier have to do with colonoscopy screening?

From 1 January 2023, a screening colonoscopy (G0105 or G0121) that follows a non-invasive stool-based test is itself a colorectal cancer screening test. The practitioner identifies that scenario with the KX modifier on the screening colonoscopy claim, and deductible and coinsurance do not apply to either test.

Related CASRAI Resources

• Modifiers GT and G0 — another pair whose current status is widely misreported
• Modifier KX: what you are actually attesting to — including its colorectal screening use
• Modifier 25 — for the problem addressed alongside the preventive visit
• Modifier GA: shifting liability with an ABN on file
• Modifiers GX, GY and GZ — the liability set for services outside the benefit
• Modifier 52 vs 53 — including how an incomplete colonoscopy is billed
• Modifiers 73 and 74 — the facility side of a colonoscopy that never happened
• Modifiers 95 and 93 — the other modifiers that describe circumstances rather than relationships
• Advance beneficiary notices
• The False Claims Act in billing

Sources: 45 CFR 147.130 (coverage of preventive health services), paragraphs (a)(1) to (a)(5) and (b)(1) to (b)(2), retrieved from the electronic Code of Federal Regulations; section 2713 of the Public Health Service Act. CMS Medicare Claims Processing Manual, Publication 100-04, Chapter 18 (preventive and screening services, table of contents Rev. 13709, issued 2 April 2026), Section 1.3 (waiver of cost sharing, Rev. 2233) and Section 60.1.1 (colorectal cancer screening deductible and coinsurance, Rev. 12299), including section 122 of Division CC of the Consolidated Appropriations Act, 2021 and the coinsurance phase-down; sections 1833(a)(1), 1833(b)(1), 1861(ww)(2) and 1861(ddd)(3) of the Social Security Act; sections 4103(c)(1) and 4104(b) of the Affordable Care Act. Noridian Healthcare Solutions modifier 33 guidance (last updated 24 May 2024) and modifier PT guidance (last updated 14 May 2025). USPSTF grades, ACIP recommendations and HRSA guidelines change, and the coverage obligation follows them on a one-year lag under 45 CFR 147.130(b)(1) — verify the current position for the date of service. CPT is a registered trademark of the American Medical Association; modifier meanings are described here in summary and the AMA’s descriptor text is not reproduced. General reference material, not coding advice for a specific claim — verify against your own MAC’s current guidance and the payer’s policy.