CPT Code 94726: Plethysmography billing & Medicare rates

Key takeaways

CPT Code 94726 covers plethysmography for determination of lung volumes (TLC, RV, FRC) and, when performed, airway resistance.

CMS gives 94726 the same 1.91 total RVUs in both settings, so the 2026 national payment is about $64 either way.

CPT 94729 for diffusion capacity is an add-on billable with 94726 on the same date, but spirometry pairs may need modifier -59.

Documentation needs a signed order, a medical necessity note, a full test report with interpretation, and the interpreter’s credentials.

Practice management software like Pabau connects to Claim.MD, so 837P claims, eligibility checks, and denial tracking sit in one workflow.

CPT Code 94726 is the billable code for plethysmography for determination of lung volumes and, when performed, airway resistance.

It covers the body-box test that measures total lung capacity, residual volume, and functional residual capacity. Spirometry cannot produce any of those three on its own.

This guide covers the official descriptor and what Medicare pays. It then works through the ICD-10 codes that support medical necessity, the documentation payers expect, and the errors that get plethysmography claims denied.

What CPT Code 94726 covers

The American Medical Association (AMA) defines CPT Code 94726 as: “Plethysmography for determination of lung volumes and, when performed, airway resistance.” It sits in the Pulmonary Diagnostic Testing and Therapies section of the CPT code set (94010-94799).

Two parts of that descriptor matter for billing. Lung volume determination is the primary purpose of the test. Airway resistance is incidental, captured “when performed” during the same plethysmographic session. It never triggers a separate code, so both components sit under one charge.

What body plethysmography measures

A body plethysmography session places the patient inside an airtight booth, known as a body box. It then measures pressure and volume changes as the patient breathes against a closed shutter. The result is a set of static lung volume measurements that spirometry cannot produce on its own.

The four primary measurements captured under CPT Code 94726 are listed below. Understanding each one helps coders confirm that the test performed matches the code billed.

• Total lung capacity (TLC): the total volume of air in the lungs at full inspiration. Elevated TLC indicates hyperinflation, as in emphysema or air trapping. Reduced TLC points to restrictive disease.
• Residual volume (RV): the air remaining in the lungs after a full exhalation. Spirometry cannot measure it, so plethysmography is required.
• Functional residual capacity (FRC): the volume of air remaining after a normal passive exhalation. FRC is the reference point from which plethysmographic measurements are made.
• Airway resistance (Raw): the opposition to airflow in the airways, measured when the shutter is closed. Elevated Raw shows up in asthma and COPD exacerbations. It is captured incidentally during the plethysmographic maneuver, where the equipment supports it.

None of these measurements require a separate code. All four are bundled within a single CPT Code 94726 charge per session.

What Medicare pays for 94726

Medicare pays for CPT Code 94726 under the CMS Physician Fee Schedule (PFS). Most pulmonary function codes pay less in a facility than in an office, because the practice expense relative value units drop. 94726 is the exception. CMS assigns it the same 1.91 total RVUs in both settings, so the site of service does not change the payment.

Geographic adjustment still does, through the Geographic Practice Cost Index (GPCI). The table below shows the 2026 national unadjusted figures, before any GPCI adjustment. They come from the CMS relative value unit file and the CY2026 conversion factor of $33.4009.

That flat payment has one practical consequence. A wrong place-of-service code on a 94726 line will not shift the money either way. It still creates audit exposure, and it can misprice other codes on the same claim.

Important: these are national figures before geographic adjustment. Check your own Medicare Administrative Contractor (MAC) fee schedule before you use them for revenue projections, since CMS updates the schedule each January.

How 94726 fits with the other pulmonary function codes

Plethysmography is one of several pulmonary function tests (PFTs) a pulmonology practice bills regularly. Knowing where 94726 sits in the code family prevents both undercoding and improper bundling.

When to bill 94726 with 94729

CPT 94729 (diffusion capacity, or DLCO) is an add-on code. It cannot be billed without a primary pulmonary function code on the same claim. When a patient has plethysmography and a DLCO measurement on the same date, bill 94726 as the primary. Add 94729 as the add-on, with no modifier.

DLCO testing is frequently ordered alongside plethysmography in interstitial lung disease workups. Both volume restriction and impaired gas transfer are expected findings there, so billing both codes captures the full clinical work performed.

How spirometry codes differ from plethysmography

Spirometry measures airflow dynamics such as FEV1, FVC, and the FEV1/FVC ratio. Plethysmography measures static lung volumes. The two use different equipment and answer different clinical questions, so a patient can legitimately need both at one visit.

Whether you can bill 94726 and a spirometry code on the same date depends on the National Correct Coding Initiative (NCCI) edits. CMS updates its Procedure-to-Procedure (PTP) edit tables quarterly. Where an edit carries a modifier indicator of “1,” modifier -59 (Distinct Procedural Service) may permit separate billing.

Check the current CMS PTP edit tables before you submit both codes. Then document that each test was clinically necessary and performed as a distinct procedure.

ICD-10 diagnosis codes that support the claim

Medicare Administrative Contractors decide which diagnoses count as a medically necessary indication for body plethysmography. They do it through Local Coverage Determinations (LCDs).

The table below lists ICD-10-CM codes that LCDs commonly accept, but covered diagnoses vary by region. Check your own MAC’s current LCD before you rely on any of them.

Coding tip: use the most specific ICD-10-CM code available. Symptom codes (R06.xx) are appropriate when a diagnosis has not yet been established, but they carry higher denial risk than confirmed etiology codes.

Document the clinical rationale in the chart note whenever a symptom code is the lead diagnosis on a plethysmography claim. Our ICD-10-CM code library carries the full descriptors if you need to confirm one before it goes on the claim.

Documentation requirements for a payable claim

Thin documentation is the largest single driver of 94726 denials, across both Medicare and commercial payers. The checklist below reflects the elements CMS guidance and MAC LCDs commonly require. Have a certified coder (CPC) review the protocol before your practice finalizes it.

• Signed physician order: a written or electronic order from the referring or treating physician, specifying the test required. Orders scanned into the record at time of service satisfy most payer requirements.
• Medical necessity justification: the chart note must document the signs, symptoms, or diagnosis that make plethysmography necessary. A bare ICD-10 code on the claim form is not enough. The note has to carry the clinical reasoning.
• Complete test report: the report must include every measured value, meaning TLC, RV, FRC, and Raw where it was measured. It also needs reference values, percent-predicted calculations, and an interpretation by a qualified provider.
• Interpreter credentials: the interpreting physician’s or qualified non-physician practitioner’s (NPP’s) credentials must be documented. Many payers require the interpreter to be the ordering provider or a physician within the same group.
• Patient cooperation note: ATS/ERS standards require documentation that the patient performed acceptably reproducible maneuvers. Note the number of acceptable attempts and any limits on patient effort.
• Superbill or encounter form: the form should capture 94726, any add-on code, and the correct place-of-service code. It has to do that before the claim is generated.

Medicare and commercial payer coverage rules

Medicare covers body plethysmography when it is medically necessary for the diagnosis or management of a pulmonary condition. Coverage is governed at the MAC level through LCDs. CMS Article A57225 addresses respiratory care billing broadly and lists pulmonary function testing as a covered service category.

Four coverage rules decide most plethysmography claims:

• Frequency limits: most MAC LCDs cap plethysmography at once per 12-month period for stable, managed conditions. Patients with rapidly progressing disease or post-treatment reassessment may qualify for more frequent testing with supporting documentation. Limits vary by MAC, so check your contractor’s LCD.
• Non-covered scenarios: pre-operative clearance for non-pulmonary surgery is not a covered indication under most LCDs, unless an active pulmonary condition is present. Routine screening with no symptoms or diagnosis is similarly non-covered.
• Commercial payer variation: commercial payers may follow CMS LCD criteria, apply their own policies, or require prior authorization. Verify coverage and authorization requirements before scheduling the test. Checking eligibility at the point of scheduling catches an authorization requirement before the patient arrives.
• Advance Beneficiary Notice (ABN): where Medicare coverage is uncertain for a specific encounter, issue and obtain a signed ABN before performing the test. That shifts financial liability for non-covered services to the patient and protects the practice from write-off exposure.

Common billing errors and how to avoid them

Plethysmography claims fail for a predictable set of reasons. Five account for most of what a pulmonology practice sees come back, and each one enters at a different stage of the encounter.

• Billing 94726 and 94727 for the same measurement: both codes measure lung volumes, 94726 by plethysmography and 94727 by gas dilution. Billing both for the same determination on the same date is duplicate billing. Bill only the method used.
• Missing physician interpretation: the report must include a separate interpretation note signed by a qualified physician or NPP. Technician-only reports are not billable under 94726. Payers treat a missing interpretation as evidence that the professional component was never performed.
• Wrong place-of-service (POS) code: a hospital-based plethysmograph in a room the hospital owns takes POS 22, not POS 11. On 94726 the payment is the same either way. The wrong POS still creates audit exposure, and it can misprice other codes on the same claim.
• Dropping a code instead of adding modifier -59: an NCCI flag between 94726 and a spirometry code does not mean the spirometry line is wrong. Where both tests were performed and separately indicated, append modifier -59 to the secondary code. Then document the distinct clinical necessity for each test in the chart note.
• Thin documentation for medical necessity: payers running post-payment audits routinely recover funds when the record does not reflect a covered indication.
  • A pulmonary practice that keeps billing plethysmography for pre-operative assessment, with no co-existing pulmonary diagnosis, will build up audit exposure. Strong denial management in healthcare practice includes pre-claim documentation audits that catch this before submission.

How Pabau supports plethysmography billing

A pulmonary function test passes through five handoffs before it becomes money. The order, the test session, the interpretation, the encounter form, and the claim are each touched by a different person. Software that connects those steps electronically keeps the claim in step with what the practice did.

Practice management software like Pabau connects to Claim.MD for 837P electronic claim submission to thousands of US payers. Our claims management software also runs eligibility checks before the patient is seen, posts ERA (835) files against the right invoice, and flags underpayments. Built-in CPT and ICD-10 catalogs sit inside the billing screen, so coding staff pick a code without leaving the workflow.

For a pulmonology practice, that means a plethysmography encounter moves from signed report to submitted claim with nobody re-keying the codes. Fewer denials come back from transcription slips, and the money arrives sooner.

Practices with high pulmonary function volume get the most out of pre-submission scrubbing. The scrub surfaces NCCI conflicts between 94726 and a spirometry code before the claim leaves the building. Catching a modifier requirement there, rather than in a denial queue, is the most direct way to protect the payment.

Streamline your pulmonary billing workflow with Pabau

Pabau integrates with Claim.MD to support electronic claim submission, eligibility checks, and ERA posting for pulmonology practices. See how a connected billing workflow reduces denials and cuts administrative time.

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Conclusion

The coding side of 94726 is settled. The descriptor is fixed, the payment is flat across both settings, and the rules for pairing it with 94729 or a spirometry code are published. What decides whether the claim pays is the paperwork behind it.

So put the effort where the denials come from. A signed order, a covered diagnosis from your MAC’s LCD, and a separately signed interpretation clear most of the risk. They do it before a claim is ever built, and a monthly sample audit catches the rest.

The trade-off worth remembering is that none of this sits with one person. The order, the interpretation, and the coded claim each come from a different desk, so the handoffs are where the money leaks. Book a demo to see how Pabau keeps a plethysmography encounter connected from order to paid claim.

Continue your research

Need to understand denial patterns for PFT codes? Denial codes in medical billing breaks down the most common claim rejection reasons and how to resolve them before resubmission.

Wondering how clearinghouse connectivity works? What is a medical claims clearinghouse? covers how 837P transactions flow from practice to payer and where scrubbing catches errors.

Looking to verify patient coverage before the appointment? Claim.MD clearinghouse review explains real-time eligibility verification and ERA posting for US practices.

Not sure what belongs on the encounter form? What is a superbill? walks through the fields a payer expects before the claim is generated.

Want to stop authorization denials at the front desk? Insurance eligibility verification shows how to confirm coverage before every visit.

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