Summary & Overview
HCPCS G9599: Aortic Aneurysm 6.0 cm or Greater on CT
HCPCS Level II code G9599 designates an imaging-documented aortic aneurysm with a maximum centerline diameter of 6.0 cm or greater, or a corresponding minor diameter on axial-formatted CT. This measurement-based code identifies patients with large aortic aneurysms, a critical threshold for clinical management decisions and care pathway activation at a national level. Accurate use of this code supports consistent reporting of aneurysm severity across imaging facilities and payers.
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of the code's clinical context, the typical service setting for CT-based measurements, and what documentation elements are relevant to coding capture. The publication outlines benchmarking and policy-relevant considerations such as coding consistency, common modifiers listed in payer guidance, and implications for claims processing and utilization tracking. Where specific data elements or payer-specific rules are not provided in the input, the text notes that data are not available.
This resource is intended for coding professionals, radiology departments, billing analysts, and policy teams seeking a clear, national-level briefing on the purpose and reporting context of HCPCS Level II code G9599.
Billing Code Overview
HCPCS Level II code G9599 describes an aortic aneurysm with maximum diameter of 6.0 cm or greater measured on centerline-formatted CT or by minor diameter on axial-formatted CT. This code captures the imaging-based size criteria that indicate a large abdominal or thoracic aortic aneurysm.
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Service type: Diagnostic imaging measurement and reporting of aortic aneurysm size on CT
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Typical site of service: Radiology or imaging center, hospital outpatient department, or other settings where CT imaging with centerline or axial reconstruction is performed
Data not available in the input.
Clinical & Coding Specifications
Clinical Context
A 72-year-old male with a history of hypertension and smoking presents for surveillance imaging after an abdominal aortic aneurysm (AAA) was previously identified. An ECG-gated contrast-enhanced CT angiography is performed with centerline measurements. Imaging documents an infrarenal aortic aneurysm with a maximum centerline diameter of 6.2 cm. The radiology team documents the maximum diameter on the centerline formatted CT and generates a structured report describing aneurysm size, involvement of iliac arteries, and suitability for endovascular repair. The vascular surgery team reviews the imaging and uses the measurement to determine urgency and operative planning. Typical clinical workflow: ordering clinician (primary care or vascular specialist) requests CT angiography; CT technologist performs contrast-enhanced study; radiologist measures centerline diameter and issues a formal report noting aneurysm >= 6.0 cm; vascular surgeon schedules consultation for repair evaluation. Typical site of service: hospital outpatient radiology department or ambulatory imaging center; potential inpatient setting if acute presentation or rupture is suspected.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
22 | Increased procedural services | Use when work required is substantially greater than typical for the CT study due to complexity (for example extensive measurements, documentation). |