Summary & Overview
CPT 94729: Lung Diffusing Capacity (DLCO) Measurement
CPT code 94729 denotes an add-on procedure that measures pulmonary diffusing capacity — the lungs' ability to move oxygen into the bloodstream and remove carbon dioxide. As a targeted physiologic test, it provides objective data on gas exchange and is frequently used in the evaluation and management of interstitial lung disease, pulmonary vascular disease, emphysema, and unexplained dyspnea. Nationally, reliable reporting of 94729 supports clinical decision-making and informs utilization patterns for advanced respiratory assessment.
Key payers discussed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise clinical context for when the test is used, typical sites of service, common billing modifiers, and payer coverage considerations. The publication presents benchmarks for utilization and reimbursement (where available), summarizes relevant policy or coverage updates affecting pulmonary function testing, and explains how 94729 interacts with related pulmonary function services in clinical workflows.
This material is intended for billing managers, respiratory clinicians, and policy analysts who need a national-level briefing on the clinical role and billing context of CPT code 94729.
Billing Code Overview
CPT code 94729 is an add-on pulmonary function procedure that measures the lungs' diffusing capacity, assessing the ability to transfer gas between the alveoli and the bloodstream — specifically oxygen uptake and carbon dioxide removal. This test evaluates the efficiency of gas exchange across the alveolar-capillary membrane and supports diagnosis and management of interstitial lung disease, emphysema, pulmonary vascular disease, and other disorders affecting diffusion.
Service Type: Pulmonary function testing — diffusing capacity (DLCO) measurement
Typical Site of Service: Pulmonary function laboratory, hospital outpatient department, or specialized respiratory clinic
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Clinical & Coding Specifications
Clinical Context
A 62-year-old patient with progressive exertional dyspnea and a history of interstitial lung disease is referred to pulmonary function testing to fully characterize gas exchange impairment. The patient presents to an outpatient pulmonary function laboratory at an academic medical center. After registration and brief clinical review, a respiratory therapist obtains informed consent, reviews contraindications (recent hemoptysis, pneumothorax, recent thoracic surgery), and performs baseline spirometry and lung volumes. The provider orders measurement of diffusing capacity for carbon monoxide (DLCO) using single-breath technique as an add-on test to the pulmonary function session. The respiratory therapist coaches the patient through breath-hold and inhalation maneuvers; gas analyzer and calibrated spirometer collect data; the supervising pulmonologist reviews the tracings and documents the interpretation. Results are used to stage disease severity, assess need for supplemental oxygen, and guide further diagnostic workup or therapy adjustments. Typical sites of service include hospital outpatient departments, free-standing pulmonary function laboratories, and ambulatory clinics equipped for respiratory testing.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when the physician interprets the test but technical component billed separately by the facility. |