Summary & Overview
CPT 87181: Antimicrobial Susceptibility Testing, Gradient Diffusion
CPT code 87181 represents a laboratory technical procedure to assess a microbial culture isolate’s susceptibility to a specific antimicrobial agent using a gradient diffusion test on an agar plate. This test informs targeted antimicrobial therapy, supports antimicrobial stewardship, and has broad clinical importance for infection management across inpatient and outpatient settings. Nationally, accurate reporting of this code affects laboratory service tracking, quality measurement, and reimbursement for microbiology testing.
Key payers referenced in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of clinical context for CPT code 87181, typical sites of service, and the service type. The publication outlines expected benchmarks and utilization patterns, common modifier usage, and policy updates relevant to lab billing and documentation where available. The content provides guidance on coding context, operational implications for clinical laboratories, and considerations for payers and compliance teams. Data not available in the input is noted where applicable.
Billing Code Overview
CPT code 87181 describes a laboratory procedure in which a lab analyst performs the technical steps to evaluate a culture isolate’s susceptibility to a specific antimicrobial agent using a gradient diffusion test device placed on an agar plate inoculated with the isolate. This procedure determines the antibiotic sensitivity of a microbial isolate and supports targeted antimicrobial therapy.
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Service type: Microbiology antimicrobial susceptibility testing (technical component)
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Typical site of service: Clinical laboratory or hospital microbiology laboratory (inpatient or outpatient lab settings)
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Clinical & Coding Specifications
Clinical Context
A typical patient is an adult hospitalized with a bloodstream infection or complicated urinary tract infection where an isolate (bacterial or fungal) has been cultured from blood, urine, wound, or other sterile site. The microbiology lab receives the culture isolate and the lab analyst performs an antimicrobial susceptibility test using a gradient diffusion device (e.g., Etest) placed on an agar plate inoculated with the isolate to determine the minimum inhibitory concentration (MIC) for a specific antibiotic. The workflow begins with organism identification (often by MALDI-TOF or biochemical testing), followed by selection of appropriate antibiotics to test based on organism and clinical history, setup of the gradient diffusion strip on the inoculated plate, incubation, and reading of the MIC at the point where the ellipse of inhibition intersects the strip. Results are documented in the laboratory information system and communicated to the ordering clinician for targeted antimicrobial therapy adjustments. Typical sites of service include hospital clinical microbiology laboratories, independent diagnostic laboratories, and outpatient reference labs that process culture isolates sent from clinics and hospitals.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when reporting only the professional component (interpretation) if applicable and separable from the technical work. |