CPC Exam Study Guide (2026) — Written to AAPC's Exam Outline

On the exam: AAPC lists Coding guidelines as 7 of the 100 questions (7 percent of the questions), and names modifier use as one of its three parts, beside the ICD-10-CM Official Guidelines and the CPT guidelines and parenthetical notes. HCPCS Level II is a separate area of 3 of the 100 questions (3 percent) that also covers modifiers (Chapter 9). Some questions from other areas also use this material: surgery, radiology, laboratory and E/M questions often turn on a modifier.

A modifier is a two-character addition that tells the payer how a service was performed without changing what the code describes. CPT modifiers are in Appendix A, HCPCS modifiers in the HCPCS Level II file. Learn what each modifier signals and the test it must pass; read the exact definition in your book.

6.1 The rules that apply to every modifier

• Justify with facts, not edits. A modifier is appended "only if the clinical circumstances justify" it and never "solely to bypass an NCCI PTP edit" (NCCI Policy Manual, Chapter I, section E).
• Four modifiers per line, payment-changing ones first (payers differ). The CMS-1500 holds four (Medicare Claims Processing Manual, Chapter 26, section 10.4, item 24D). Modifier 99 means more apply than fit, and the full list goes in item 19.

6.2 Evaluation and management modifiers: 24, 25, 57

• 24. A diagnosis that clearly shows the visit is unrelated is acceptable (Claims Processing Manual, Chapter 12, section 40.2.A.7). Prepayment edits catch global-period E/M services billed without 24, 25, 57, 78 or 79 (section 40.3.B).
• 25. NCCI allows 25 for an E/M on the day of a minor procedure (global 000 or 010) or an XXX procedure. The diagnosis may be the same or different, a new patient alone is not enough, and deciding to do a minor procedure is included in the procedure (NCCI Chapter I, sections D and E.b). 25 goes on the E/M, never on the procedure.
• 57. Medicare bills the E/M that results in the decision for a major surgery, the day before or the day of, with 57 and "not 25." Not used with minor surgery, whose global does not include the day before (Claims Processing Manual, Chapter 12, section 40.2.A.4).

6.3 Global-period surgery modifiers

Chapter 10 explains the global package; these modifiers describe who did what inside it.

Medicare rules (Claims Processing Manual, Chapter 12, sections 40.2.A and 40.8).

• 58 and 79. Both start a new postoperative period. 58 is not for a problem that requires a return to the OR (sections 40.2.A.6-7).
• 78. Needs a return to a place "specifically equipped and staffed for the sole purpose of performing procedures": for example a cardiac catheterization, laser or endoscopy suite. A patient room, minor treatment room, recovery room or ICU generally does not (section 40.1.B). Bill the code for the procedure done on the return, not the original code, unless the identical procedure repeats (section 40.2.A.5).
• 54 and 55. Same date of service, same procedure code, written transfer of care. The receiving physician cannot bill until providing at least one service (section 40.2.A.3). 56 is CPT-only.
• 62. Each co-surgeon is paid 62.5 percent of the fee schedule amount. Team surgery (66) is paid by report (section 40.8.B).
• 80, 81, 82, AS. Physician assistant-at-surgery payment is 16 percent of the amount otherwise applicable. Medicare may not pay an assistant where physicians assist in fewer than 5 percent of cases (section 20.4.3), or when co-surgeons or a team are paid (section 40.9).

6.4 Multiples, bilateral, repeats, reduced and discontinued services

50 (bilateral). For a procedure not already described as bilateral, Medicare wants one line with 50, paid at 150 percent when the bilateral indicator is 1. The manual notes this "differs from the CPT coding guidelines" (two line items) (Chapter 12, section 40.7.B). If the descriptor already says bilateral, or "unilateral or bilateral," do not add 50.

51 (multiple procedures). Medicare says to report the major procedure without 51 and additional ones with 51 (Chapter 12, section 40.6.B), but its system finds multiples on the same day anyway (section 40.6.C.1), so the reduction does not depend on 51. Some MACs say not to append 51 at all because their system adds it (Noridian JF Part B, September 30, 2025). Never append 51 to add-ons or codes designated exempt.

52 and 53. 52 is reduced services, 53 is discontinued. For 22 and 52 Medicare requires a short statement of how the service differs and the operative report (section 40.2.A.10). For 53, the Fee Schedule carries separate RVUs only for colonoscopy codes 44388 and 45378 (and HCPCS G0105 and G0121), paid since 2016 at a rate built from one-half the value of the code's inputs (section 30.1.B). Other codes with 53 are individually priced (CMS RVU26D). 53 is for physician services, not hospital outpatient services (Claims Processing Manual, Chapter 4, section 20.6.4).

73 and 74. Facility versions for hospital outpatient and ASC procedures. 73 is discontinued before anesthesia, paid at 50 percent of the OPPS rate. 74 is discontinued after anesthesia or the start of the procedure, paid at the full rate (Chapter 4, section 20.6.4).

76 and 77. Repeat procedure by the same physician (76) or another physician (77). Neither is PTP-associated, so neither bypasses an edit (NCCI Chapter I, section E).

91, 90, 92. 91 repeats a clinical lab test the same day when medically necessary (NCCI Chapter I, section N); Appendix A limits it further. 90 is reference (outside) laboratory. 92 is CPT's alternate laboratory platform modifier.

6.5 Distinct services: 59 and the X modifiers

NCCI procedure-to-procedure (PTP) edits are code pairs: the Column One code is paid and the Column Two code is denied unless a PTP-associated modifier is clinically appropriate (section A). The PTP-associated modifiers are the anatomic ones (LT, RT, E1-E4, FA, F1-F9, TA, T1-T9 and a few others), the global surgery ones (24, 25, 57, 58, 78, 79), and 27, 59, 91, XE, XS, XP, XU (section E). 22, 76 and 77 are not.

Each edit carries a Correct Coding Modifier Indicator: 0 means PTP-associated modifiers cannot bypass it; 1 means they may, when the facts fit; 9 means "not specified" (section E). Find it on the PTP edit table.

59 shows two procedures at different anatomic sites or different patient encounters. NCCI says it "shall only be used if no other modifier more appropriately describes" the relationship, and that XE, XP, XS and XU "may be used in lieu of modifier 59 whenever possible" (Chapter I, sections E.d and E.e).

Different diagnoses are not enough: the codes "remain bundled unless the procedures/surgeries are performed at different anatomic sites or separate patient encounters" (section E.d).

6.6 Professional component, technical component, and special-circumstance modifiers

26 and TC. 26 is the professional component (the interpretation); TC is the technical component (equipment and staff). The Fee Schedule PC/TC indicator decides which applies. Indicator 1 codes accept 26 and TC. Indicator 2 codes (93010, ECG interpretation) are professional only and indicator 3 codes (93005, ECG tracing) technical only; on both, 26 and TC "cannot be used" (CMS RVU26D, Attachment A). No modifier means the global service.

22 (increased procedural services). Substantially more work than usual. Medicare asks for a short statement and the operative report, and 22 applies only to codes with a global period of 0, 10 or 90 days (section 40.2.A.10). Payment rises only in "very unusual circumstances" (section 20.4.6). 22 does not bypass an NCCI edit (NCCI Chapter I, section E.a).

6.7 HCPCS Level II modifiers

Titles are from the HCPCS Level II file, October 2026 release.

• Anatomic: LT, RT, E1-E4 (eyelids), FA and F1-F9 (fingers), TA and T1-T9 (toes). They are PTP-associated and can bypass an edit when sites really differ.
• ABN family (Chapter 4): GA (waiver of liability statement on file), GX (voluntary notice of liability), GY (statutorily excluded), GZ (expected to be denied as not reasonable and necessary).
• KX and QW: KX means the medical policy's requirements are met (documented compliance, not a way around denial). QW is a CLIA waived test. Anesthesia modifiers are in Chapter 21.
• JW and JZ: JW reports drug amount discarded; JZ reports none was. Since July 1, 2023, Medicare requires JZ on separately payable single-dose container drugs when nothing was discarded; discarded amounts go on a second line with JW. Neither applies to multi-dose containers (Claims Processing Manual, Chapter 17, section 40).
• Telehealth: CMS names POS 02 (patient not at home) or POS 10 (at home) for Medicare professional claims; the POS sets the rate (CMS Telehealth FAQ, updated 10/8/26, Q8). The Claims Processing Manual also pairs the POS with 93 (audio-only) or 95 (audio and video) (Chapter 26, section 10.5, CY2024 text); the FAQ does not repeat that, so check your MAC.
• GC and FT: GC means a resident performed part of the service under teaching physician direction. FT marks an unrelated E/M on the same day as another E/M or during a global procedure period (HCPCS file; Chapter 12, section 40.2.A.9).

6.8 Reading the payment indicators in the Fee Schedule file

The CMS relative value file (RVU26D layout, CY2026; examples from the October 2026 release) gives each code these indicators.

Indicator 9 fills every field for bundled codes such as 99024. For endoscopy indicator 3 the file carries the family's base code (29881 shows 29870). The bilateral adjustment is applied before the multiple-procedure ranking (RVU26D). Chapter 10 works the arithmetic.

Key facts

• 24, 25, 57 go on E/M codes; 58, 78, 79 on procedures in a global period. Medicare uses 57, not 25, for a decision for major surgery (Ch. 12, section 40.2.A.4).
• 58 planned, 78 unplanned related return to the OR, 79 unrelated.
• Medicare: 50 is one line, 150 percent when the indicator is 1. 62 pays 62.5 percent each. Assistant is 16 percent. Team is by report.
• 59 only when no more specific modifier fits; XE, XS, XP, XU are more specific (NCCI Ch. I, section E).
• PTP-associated modifiers bypass an edit only when its indicator is 1 and the facts fit. 22, 76, 77 never do.
• 73 and 74 are the facility pair; 53 is not for outpatient hospital services.