CPT code 17315: Mohs surgery billing for trunk, arms, and legs

Key Takeaways

CPT code 17315 is an add-on code for Mohs micrographic surgery on the trunk, arms, or legs, reporting each additional block after the first two during the first stage.

It must always be billed alongside CPT 17313, the primary first-stage code for trunk, arms, and legs. Never bill 17315 as a standalone code.

The most common denial trigger is billing 17315 without 17313, or applying it to the wrong anatomical site. Site documentation in the operative report is non-negotiable.

Pabau’s claims management software helps dermatology practices pair add-on codes correctly, flag site mismatches before submission, and reduce Mohs billing denials.

CPT Code 17315 is defined by the American Medical Association as: Mohs micrographic surgery for malignant neoplasm; trunk, arms, or legs; each additional block after the first two blocks during the first stage. The AMA designates it as an add-on code, which means it cannot be billed independently.

Three criteria must all be true before CPT Code 17315 applies:

• Anatomical site: trunk, arms, or legs only (not the head, neck, hands, feet, or genitalia)
• Stage: first stage only (the code is not used for subsequent stages)
• Block count: each block beyond the first two processed during that first stage

If a surgeon processes five blocks during the first stage on a patient’s back, CPT 17313 covers the first block and CPT Code 17315 is reported three times (once per block after the first two). Each additional block gets its own unit of 17315.

The Mohs surgery CPT code family: 17311 to 17315

CPT Code 17315 is one of five codes in the Mohs micrographic surgery family. Understanding where it sits within the family is essential before billing any Mohs case. The primary codes (17311 and 17313) anchor each claim; the add-on codes (17312, 17314, and 17315) are built on top of them.

The most common source of confusion is the distinction between 17314 and 17315. Both are add-on codes for trunk, arms, or legs and both require 17313 as the primary code. The difference: 17314 applies to each additional stage after stage 1, while CPT Code 17315 applies to each additional block beyond the first two within stage 1. Wrong code selection here consistently triggers payer edits.

When to use CPT 17315: Add-on code rules

CPT Code 17315 fires only when all three conditions below are met simultaneously. Meeting two of three is not enough.

1. The lesion is on the trunk, arms, or legs. Head, neck, hands, feet, and genitalia use a different code family (17311/17312). The operative report must document the anatomical site explicitly.
2. You are still in stage 1 of the procedure. CPT Code 17315 does not apply to stage 2 or later. Once you move to a subsequent stage, the applicable code changes to 17314.
3. The block count exceeds two. The first two blocks during stage 1 are already covered by 17313. Report one unit of CPT Code 17315 for each block processed after those first two.

17313 vs 17315: Primary code vs add-on code

CPT 17313 is the foundation. It covers Mohs surgery of the trunk, arms, or legs during the first stage, up to and including the second block. CPT Code 17315 stacks on top of 17313 for every block beyond that threshold. On a claim where the surgeon processed four blocks in stage 1 on a patient’s shoulder, the correct coding is 17313 x1 and CPT Code 17315 x2. Never reverse that relationship. Never report 17315 without 17313 on the same claim.

Medicare reimbursement rates for CPT code 17315 (2026)

Medicare pays different rates depending on where the procedure is performed. Non-facility settings (physician offices, standalone dermatology practices) receive a higher rate because the practice bears overhead costs. Facility settings (hospital outpatient departments, ambulatory surgery centers) receive a lower physician component rate because the facility bills separately for overhead.

According to fee schedule data from CMS Physician Fee Schedule lookup, the 2026 indicative rates for CPT Code 17315 are approximately:

These figures are indicative and subject to annual MPFS adjustment. Always verify the current-year rates directly via the CMS MPFS lookup tool before quoting reimbursement internally. Commercial payer rates for CPT Code 17315 vary by contract and are typically higher than Medicare rates. Verify with each payer’s fee schedule or provider portal.

Dermatology practices tracking revenue per procedure benefit from claims management software that flags when the reimbursed amount falls outside expected ranges for a given code, setting, and payer combination.

Medicare coverage criteria for Mohs surgery

Medicare covers Mohs micrographic surgery under LCD L30713, the local coverage determination maintained by the relevant MAC. Coverage requires documented medical necessity, which generally means the tumor meets one or more of these criteria:

• Malignant histology confirmed (basal cell carcinoma or squamous cell carcinoma are the most common indications)
• Tumor location in a high-risk area or recurrent after prior treatment
• Aggressive histologic subtype (morpheaform, infiltrative, perineural involvement)
• Tumor size meeting threshold criteria per the LCD (size thresholds vary by anatomical site)
• Patient immunocompromised or with high surgical risk requiring tissue conservation

The operative note must connect each of these factors to the patient’s specific presentation. A generic “medically necessary” statement without supporting clinical detail does not satisfy LCD requirements. Some MACs require the surgeon to document why standard excision was inadequate.

Prior authorization requirements for Mohs surgery vary by commercial payer. Medicare does not require prior authorization for Mohs procedures, but many commercial plans do. Verify with each payer before scheduling, particularly for UnitedHealthcare (UHC Policy R6008) and Aetna. Document the authorization number in the patient’s record and on the claim.

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ICD-10 codes used with CPT 17315

CPT Code 17315 must be paired with an ICD-10-CM diagnosis code that reflects the confirmed malignancy. The diagnosis code must match the documented histology and anatomical site. Using a benign lesion code or an unspecified site code when a specific site is documented will trigger a payer edit.

Always select the most specific code available. If pathology confirms basal cell carcinoma of the right shoulder, code C44.611, not the unspecified trunk code. Specificity matters for medical necessity review, LCD compliance, and claim payment. Practices managing dermatology billing can use digital intake forms to capture anatomical site and clinical details at consultation, reducing transcription errors that propagate into ICD-10 code selection.

Documentation requirements for Mohs surgery billing

Inadequate documentation is the leading cause of post-payment audits in Mohs surgery billing. The operative report must support every unit of every CPT code reported on the claim. For CPT Code 17315 specifically, the record must demonstrate that the block count genuinely exceeded two during the first stage.

• Total number of stages performed: document each stage clearly, with start and completion notation
• Blocks processed per stage: every block in stage 1 must be individually enumerated. If five blocks were processed, the report should state “five tissue blocks processed during stage 1”
• Anatomical site: specify the body region (e.g. “right posterior shoulder”) to support the trunk/arms/legs site requirement for 17315
• Surgeon-pathologist identity: Medicare requires that the operating surgeon also perform the pathological examination. Document that the Mohs surgeon interpreted the frozen sections
• Frozen section pathology results: record the margin status for each block at each stage
• Medical necessity rationale: connect the tumor characteristics (histology, size, location, prior treatment history) to the decision to perform Mohs surgery
• Reconstruction plan: if reconstruction was performed, document it separately. Repair codes are not included in the 17315 global package and must be supported by their own documentation

Practices using structured patient records with procedure-specific note templates capture this data at the point of care, reducing the scramble to reconstruct documentation during a payer audit. The dermatology EMR software a practice uses should make the Mohs operative note fields non-optional, not an afterthought.

Common billing errors and denials for CPT code 17315

The table below covers the denial patterns billing staff encounter most often with CPT Code 17315, along with the corrective action for each.

Denial management for Mohs claims is less about appeals and more about front-end claim scrubbing. Catching a block count error before submission takes 30 seconds. Appealing a denial after the fact takes weeks. The best practice management software for dermatology integrates claim editing rules that flag these specific coding relationships before the claim leaves the practice.

Streamlining Mohs surgery billing with practice management software

Mohs billing is structurally different from most dermatology procedures. The number of code units changes dynamically based on intraoperative findings, the block count is not fixed at scheduling, and the code pairing rules are strict. That combination creates a higher-than-average error rate when billing teams rely on manual code entry.

Practice management platforms designed for dermatology handle several of the failure points directly. When a billing team builds a charge from an operative note in skin clinic software, the system can enforce that 17315 cannot be saved without 17313 on the same encounter, automatically calculate the correct number of 17315 units from the documented block count, and flag ICD-10 codes whose body site does not align with the CPT code’s site requirement.

Documentation workflows matter equally. When surgeons dictate or complete structured operative notes inside the practice management system rather than in a separate platform, the block count and anatomical site data populate directly into the charge capture workflow. That single-source-of-truth approach eliminates the transcription step where most block count errors originate. Practices interested in reducing documentation burden for complex surgical cases can explore how structured CPT coding workflows apply across different specialties, or review how other dermatology billing scenarios like complex add-on code families benefit from the same approach.

Payer-specific rules for Mohs surgery, including UHC Policy R6008 and individual MAC LCD requirements, can be stored as billing rules within the platform so that prior authorization reminders trigger for the right payers automatically. Rather than relying on a staff member to remember which commercial plans require auth for Mohs, the system flags the requirement at scheduling when it detects the patient’s insurance plan. The compliance requirements that govern clinical documentation for these procedures are equally important to maintain systematically rather than manually.

Conclusion

CPT Code 17315 is a precise add-on code with three non-negotiable criteria: trunk, arms, or legs; first stage; blocks beyond the first two. Get any one wrong and the claim denies. The operative report is the single document that ties every requirement together, which makes documentation quality the most important variable in Mohs billing accuracy.

Pabau’s claims management software helps dermatology teams enforce add-on code pairing rules, verify block counts against documented operative data, and reduce the manual errors that drive Mohs denials. To see how it fits a dermatology billing workflow, book a demo with the Pabau team.

Continue your research

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