CPT® Code 78815

Last Updated: January 2026 | Verified for 2026 Medicare/CMS and commonly applied payer coding rules

Quick Reference: CPT 78815

• Definition: PET with concurrently acquired CT for attenuation correction and anatomical localization, covering skull base to mid-thigh .
• Clinical role: Standard oncologic FDG PET/CT extent used for most solid tumors and lymphoma staging/restaging; commonly described as the most frequently ordered PET exam field-of-view in oncology practice .
• CT component: The CT within 78815 is typically for localization/attenuation. A separate diagnostic CT (e.g., contrast CT chest) requires its own order, technique, and report and is billed separately .
• Medicare oncologic modifiers: Use PI for initial treatment strategy and PS for subsequent treatment strategy; for additional scans beyond usual limits, KX may be required with PS depending on the coverage situation .
• Component billing: Use TC for technical component and 26 for professional interpretation when split billing is needed .
• Radiopharmaceutical: For FDG studies, report A9552 (FDG, per study dose up to 45 mCi) on the claim; payment may be packaged in some settings but the code is commonly required for claim completeness . CPT 78815 is the workhorse PET/CT code for oncologic imaging when the acquisition spans from the skull base through the mid-thigh. Correct coding hinges on three things: (1) the documented scan extent, (2) the clinical indication and diagnosis coding that establish medical necessity, and (3) payer-specific requirements—especially Medicare’s PI/PS modifier framework and commercial payer preauthorization workflows.

This guide explains how to document 78815 in a way that supports payment, how to choose 78815 vs 78814 vs 78816 based on what was actually imaged, and how to avoid common errors such as billing an extra diagnostic CT without a separate order/report. It also outlines how to code radiopharmaceuticals (FDG and beyond) and how to structure claims when the technical and professional components are billed by different parties.

1. Code Definition & Standard PET/CT Protocol

CPT 78815 describes a PET scan with concurrently acquired CT for attenuation correction and anatomical localization covering the area from the skull base to mid-thigh .

Operationally, “skull base to mid-thigh” is interpreted as imaging that begins below the calvarium (excluding dedicated intracranial/brain coverage) and extends through the pelvis into the proximal femora. This field-of-view is the typical default in oncology because it captures many common metastatic pathways (cervical/supraclavicular nodes, mediastinum, abdomen/pelvis, and proximal skeletal involvement) without necessarily extending to distal extremities.

A conventional FDG PET/CT workflow includes: patient preparation (often fasting and glucose assessment), intravenous administration of FDG, an uptake period commonly around 60 minutes, and then integrated CT and PET acquisitions performed in one session with the patient on the same table. The PET data reflect radiotracer distribution and are fused with CT for localization and attenuation correction, enabling co-registered functional and anatomical interpretation . In practical coding terms, the “concurrently acquired CT” is integral to the PET/CT procedure described by 78815 and is not separately reported unless a distinct diagnostic CT is performed and appropriately documented.

The Northern California PET Imaging Center overview notes that this skull base-to-mid-thigh exam is commonly ordered and outlines typical oncology uses and distinctions compared with truly head-to-toe protocols . For coding and compliance, the relevant point is that the actual scan range must be clearly stated in the technique portion of the report and must match the CPT code billed.

Audit-sensitive distinction: Coding guidance emphasizes that if the scan is not truly whole-body head-to-toe, 78816 should not be billed; conversely, if imaging is limited to a single region, 78814 (limited area) may be the correct code. Documentation of scan extent is the first line of defense in extent-related denials .

2. Documentation & Medical Necessity Standards

Because PET/CT is high-cost imaging and is frequently subject to payer review, documentation must establish that the test is reasonable and necessary for the patient’s condition. Medicare-oriented billing and coding guidance for PET in specific contexts (such as inflammation and infection indications) explicitly emphasizes complete history, rationale, report content, and correct coding as prerequisites for coverage determination . The same documentation principles are applied in oncology, even when coverage is broad.

Required elements

• Clinical indication and question: Document why PET/CT is ordered (e.g., “initial staging of biopsy-proven NSCLC,” “evaluate suspected lymphoma relapse,” “assess treatment response after 2 cycles”). Medicare’s oncologic PET framework centers coverage on whether the scan informs treatment strategy rather than routine screening .
• Relevant prior data: Include pathology confirmation when available, prior imaging results, tumor markers, or clinical changes that prompted the exam (new symptoms, rising markers, equivocal CT/MRI). This helps demonstrate that PET/CT is being used to answer a specific decision-point question.
• Technique documentation: Record radiopharmaceutical, dose, route, uptake time, and scan extent (explicitly state skull base to mid-thigh for 78815). Radiology coding discussions highlight technique description and extent as key components of compliant PET documentation .
• Interpretive report: Provide a signed physician interpretation with findings and impression. The impression should tie results to management when possible (staging implications, suspected metastases, response assessment). Contractor documentation guidance underscores the importance of a complete report and availability of records upon request .

Diagnostic CT performed in addition to PET/CT

A frequent denial driver is billing a separate diagnostic CT when only the low-dose CT for localization/attenuation was performed. Radiology coding guidance explains that if a diagnostic-quality CT is needed (for example with contrast or a dedicated diagnostic protocol), it must be ordered separately and have a distinct report . The documentation must support why that diagnostic CT was medically necessary beyond what the PET/CT already provides. If the diagnostic CT is performed, it should not be “hidden” inside the PET/CT report in a way that obscures whether a separate diagnostic service occurred.

A practical compliance strategy is to document two clearly labeled sections (or two reports): (1) PET/CT report (with localization CT described), and (2) separate diagnostic CT report with its own technique, contrast use (if any), and impression. This structure reduces the chance of payer edits bundling or denying the diagnostic CT as duplicative.

Example Documentation (Compressed)

Indication: Biopsy-proven NSCLC, initial staging.

Radiopharmaceutical: FDG administered IV; uptake ~60 minutes.

Technique: PET/CT from skull base to mid-thigh, CT for attenuation correction and localization.

Findings: Hypermetabolic RUL lung mass; FDG-avid mediastinal nodes; no distant FDG-avid metastasis.

Impression: PET stage consistent with nodal disease; results guide initial treatment strategy.

3. ICD-10 Indications & Diagnosis Coding Rules

For oncology, the strongest ICD-10 support for CPT 78815 is an active malignancy code in the C00–C96 ranges. Examples commonly used in claims include lung cancer (C34.90), breast cancer (C50.919), colorectal cancer (C18.9), lymphoma (C81.xx or C85.90), melanoma, and many others. Medicare’s coverage framework is broad for FDG PET/CT across cancers when the scan is used for initial treatment planning or subsequent treatment strategy decisions .

Diagnosis coding should align to the reason the scan is being performed. For example:

• Initial staging: Use the active cancer code (and site-specific codes when available). This supports that the scan is intended to guide the first treatment strategy decision.
• Suspected recurrence: Use the cancer code when active disease is suspected or being evaluated; if the patient is in remission with a history code (Z85.xx), many payer rules expect an additional code reflecting the clinical trigger (e.g., suspicious imaging finding, symptom, or marker elevation). Medicare-oriented coverage summaries note that history-only coding is not sufficient by itself and that claims should indicate an active evaluation context . Non-oncologic indications (inflammation/infection, FUO) are more variable and often depend on local policies. CGS’s article on PET for inflammation and infection describes documentation expectations and an FUO example (fever persisting ≥21 days after standard workup) and highlights the importance of ICD-10 coding such as R50.9 to support coverage in qualifying scenarios . When billing 78815 outside oncology, the record should explicitly show that the indication meets the payer’s specific coverage criteria; otherwise, the scan may be denied as investigational or not covered.

Important Medicare exception cited in coverage summaries: Medicare coverage references note that certain PET codes (78811–78816) are not covered for the initial diagnosis/initial staging of cervical cancer (ICD-10 C53.x) in the referenced coverage compilation . When cervical cancer is the indication, confirm whether the scan is truly initial staging (potentially noncovered in that framework) versus subsequent management/restaging (often treated differently).

4. Medicare vs. Commercial Coverage & Utilization Controls

Although oncology PET/CT is widely accepted, coverage and payment are influenced by payer rules, utilization management, and documentation standards. Medicare uses a national coverage structure for oncologic FDG PET to distinguish scans used for initial treatment strategy from scans used for subsequent treatment strategy and to limit routine use that does not affect management . Commercial payers typically cover similar core indications but implement preauthorization and may have additional prerequisites.

Medicare: Initial and subsequent treatment strategy framework

Medicare’s oncologic PET coverage is often summarized as allowing one PET scan for initial treatment strategy and up to three subsequent treatment strategy scans per cancer diagnosis, with additional scans requiring attestation and case-by-case review . Operationally, this is why Medicare requires PI/PS modifiers for oncologic PET claims: they enable the payer to track whether a scan counts as initial or subsequent strategy and to apply any frequency logic.

If the clinical situation requires additional scans beyond typical thresholds, guidance describes appending modifier KX (with PS) to attest that coverage requirements are met for an additional scan, acknowledging that the claim may be reviewed . Because KX is an attestation, it should be supported by documentation that a new management decision is pending (therapy change, ambiguous findings that alter treatment, suspected progression with actionable implications).

Commercial payers: Policy criteria plus authorization

Commercial payers generally align oncologic coverage to evidence-based guidelines, but nearly always require preauthorization. Aetna’s PET clinical policy bulletin illustrates the typical commercial policy approach: detailed criteria by cancer type, scenario (staging vs restaging), and tracer type, including newer oncologic tracers under defined conditions . In addition, some BlueCross/BCBS medical coverage guidelines distinguish covered oncologic applications from investigational uses and emphasize documentation aligned to specialty society guidance .

Preauthorization is not merely administrative: absence of authorization is a common cause of denial even when medical necessity is strong. Industry reporting on payer utilization management has documented insurer expansion of prior notification requirements for advanced imaging including PET . Practically, imaging orders should be accompanied by succinct documentation that matches payer criteria: diagnosis, clinical question, prior workup, and how PET results will change management.

5. Modifier Rules (TC, 26, PI, PS, KX)

CPT 78815 is a global service by default (technical + professional). When the technical and professional components are provided by different billing entities, modifiers separate those components. Guidance and coding references explain that modifier TC represents the technical component and modifier 26 represents the professional interpretation for CPT 78815 .

TC and 26 (component billing)

• 78815-TC: Facility bills technical performance (scanner, technologists, supplies, equipment). Common for hospitals or imaging centers providing the scan.
• 78815-26: Physician bills interpretation only. Common when radiologists are independent from the facility.
• 78815 (global): Single claim without TC/26 when the same entity furnishes both components.

PI and PS (Medicare oncologic PET modifiers)

Medicare requires special HCPCS modifiers on oncologic FDG PET claims:

PI for PET performed for initial treatment strategy and PS for PET performed for subsequent treatment strategy . Radiology coding guidance explains the PI vs PS logic and the linkage to Medicare’s limits on subsequent scans . These modifiers should be applied consistently across technical and professional claims when split billing is used.

KX (attestation for additional scans)

When additional PET scans are needed beyond typical subsequent scan thresholds, guidance indicates the use of modifier KX with PS to attest medical necessity under the applicable coverage framework, often triggering review . KX should not be appended routinely; it should be reserved for cases where documentation supports why another PET/CT is needed to guide management and why the result will meaningfully change the treatment strategy.

6. Radiopharmaceutical Coding (A9552 and other tracers)

Claims for PET/CT typically include both the imaging procedure code (78815) and the radiopharmaceutical code for the tracer administered. For standard FDG PET/CT, the HCPCS code is A9552, defined as FDG per study dose up to 45 millicuries . Medicare coverage documents and policy notes commonly emphasize that tracer codes should be present on PET claims; in some settings payment may be packaged (for example, certain outpatient hospital billing structures), but the tracer code remains important for claim completeness and tracking .

If a non-FDG tracer is used, an appropriate tracer-specific HCPCS code must be billed instead of A9552. Commercial policies often address tracer-specific coverage, including newer oncology tracers, and may require that the tracer matches a covered indication and that authorization includes the tracer information . As a practical workflow, imaging centers should ensure that scheduling/preauth teams capture (1) the PET CPT code, (2) the tracer intended, and (3) the indication and clinical context, because some payers adjudicate PET coverage differently depending on tracer type.

Common tracer-related denial pattern: tracer code missing or inconsistent with documentation (e.g., chart states FDG but claim lacks A9552). Coverage notes indicate tracer codes are required on PET claims in the referenced Medicare compilation, even where payment is packaged .

7. Comparison: 78814 vs 78815 vs 78816

The distinction among 78814, 78815, and 78816 is the anatomic extent imaged. Coding guidance stresses that the report technique must support the billed extent; upcoding extent (billing 78816 for a scan that was only skull base to mid-thigh) is a high-visibility error because it is often contradicted by the report’s own field-of-view statement .

In summary: choose 78814 for limited region imaging, 78815 for skull base through mid-thigh, and 78816 for head-to-toe. The radiology report should make the extent unambiguous (ideally a single technique sentence that matches the billed CPT).

8. Clinical Coding Scenarios

The following scenarios show how to align clinical intent, documentation, and billing rules. They emphasize extent selection, Medicare oncologic modifiers, and non-oncologic documentation requirements.

Scenario 1: Initial staging (Medicare) — PI required

Patient: 65-year-old with biopsy-proven non-small cell lung cancer.

Action: FDG PET/CT performed from skull base to mid-thigh for initial staging and treatment planning.

Coding: 78815-PI (and TC/26 split as applicable). Include active diagnosis C34.90.

Rationale: Medicare coverage for oncologic PET includes an initial treatment strategy scan under the national framework summarized by CGS . PI communicates initial strategy and supports correct adjudication.

Scenario 2: Restaging/response assessment — PS required

Patient: 48-year-old with Hodgkin lymphoma after therapy, new enlarged nodes on exam.

Action: Skull base to mid-thigh PET/CT to evaluate recurrence and guide next treatment step.

Coding: 78815-PS; consider pairing history codes with an active evaluation trigger when needed per Medicare-oriented coding instructions .

Rationale: PS designates subsequent treatment strategy and aligns with Medicare PET coding explanations .

Scenario 3: Fourth subsequent scan — PS + KX

Patient: Metastatic disease on therapy with new symptoms; clinician needs PET to decide whether to switch regimens.

Action: Additional PET/CT beyond typical subsequent scan count for the same cancer diagnosis.

Coding: 78815-PS-KX (when the coverage situation requires attestation).

Rationale: Guidance describes KX use with PS to attest coverage requirements for additional scans beyond usual limits . Documentation should clearly show the decision point and why PET is needed.

Scenario 4: Non-oncologic FUO — local policy documentation

Patient: 70-year-old with fever of unknown origin lasting ≥3 weeks, extensive negative workup.

Action: FDG PET/CT skull base to mid-thigh to localize infection/inflammation source; scan reveals vertebral focus consistent with osteomyelitis/discitis.

Coding: 78815 (no PI/PS for non-oncologic indication), ICD-10 R50.9 with strong supporting documentation of FUO criteria.

Rationale: Contractor billing/coding guidance for PET in inflammation/infection contexts emphasizes documentation requirements and FUO criteria .

Scenario 5: Tracer coding — A9552 included for FDG

Patient: Oncology patient scheduled for FDG PET/CT staging.

Action: FDG administered; PET/CT performed as 78815.

Coding: Report 78815 and A9552 for FDG tracer dose.

Rationale: A9552 describes FDG per study dose , and Medicare-oriented notes indicate tracer codes are required on PET claims even when payment is packaged .