Summary & Overview
CPT 87186: Antimicrobial Susceptibility Testing by Dilution Methods
CPT code 87186 represents laboratory antimicrobial susceptibility testing by dilution methods, a core microbiology service that determines minimum inhibitory concentrations (MICs) for culture isolates. This testing informs antimicrobial therapy selection and surveillance of resistance patterns, making it an essential diagnostic service across inpatient and outpatient settings nationwide. The code covers technical laboratory work using agar or microdilution techniques to observe organism growth across antibiotic concentrations.
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a national-focused overview of clinical context for dilution-based susceptibility testing, typical sites of service, and common billing considerations. The publication outlines commonly observed payer coverage patterns, billing modifiers used in practice, and service-line implications for hospital and reference laboratories.
The content provides benchmarks and policy-relevant points for laboratory managers and revenue cycle staff, including where 87186 fits within microbiology service coding, operational implications for lab workflows, and elements that affect claims processing. Data not available in the input is noted where specific payer policies, fee schedules, or taxonomies are required but not provided.
Billing Code Overview
CPT code 87186 describes a laboratory procedure in which a laboratory analyst evaluates a culture isolate’s susceptibility to multiple antimicrobial agents using agar dilution or microdilution methods to determine the minimum inhibitory concentration (MIC). The procedure involves observing organism growth at varying antibiotic concentrations to establish the lowest concentration that inhibits visible growth.
Service type: Microbiology antimicrobial susceptibility testing (technical component) involving dilution methods.
Typical site of service: Clinical microbiology laboratory or hospital laboratory where culture isolates are processed and susceptibility testing is performed.
Clinical & Coding Specifications
Clinical Context
A typical adult inpatient admitted for suspected bacteremia after a central line–associated bloodstream infection presents with persistent fever despite empiric antibiotics. A blood culture grows a Gram-negative bacillus; the microbiology laboratory isolates the organism and performs antimicrobial susceptibility testing using agar or microdilution to determine minimum inhibitory concentrations. The clinical workflow: the attending or infectious disease clinician orders culture and susceptibility testing; the specimen is processed by a medical laboratory scientist who isolates the culture; the lab analyst performs 87186 technical procedures to prepare dilutions, inoculate wells or agar, incubate, and read MIC values; results are reported in the electronic medical record and communicated to the treating team for antibiotic optimization.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the professional (interpretive) component of a split-service laboratory test if applicable under local policies. |
59 | Distinct procedural service |