The Current Procedural Terminology (CPT) codes are standardized five-digit numbers used by medical professionals to describe and bill for procedures and services. CPT 93970 identifies a specific, non-invasive imaging test used routinely in the management of patients relying on hemodialysis. This diagnostic tool is designed to maintain the functionality of the patient’s vascular access, often referred to as their “lifeline.” Proper use of this code allows for the tracking and reimbursement of this important service for individuals with end-stage renal disease.
Defining CPT 93970
The full description of CPT 93970 is the “Duplex scan of arterial inflow and venous outflow of dialysis access, complete bilateral study.” A duplex scan is a sophisticated ultrasound technique that combines two different modes of imaging. The first is B-mode ultrasound, which creates a two-dimensional, real-time image of the physical structure of the blood vessels.
The second component is Doppler technology, which measures the speed and direction of blood flow within those vessels. Combining these two modalities provides both an anatomical map and a dynamic assessment of circulation. The scan is comprehensive, examining the entire pathway of the dialysis access, including the artery supplying the blood (inflow) and the vein returning the treated blood (outflow). This evaluation covers the arteriovenous fistula (AVF) or arteriovenous graft (AVG) itself.
Necessity of Monitoring Dialysis Access
Dialysis access—whether an AV fistula or an artificial graft—is the patient’s most reliable means for receiving life-sustaining hemodialysis treatment. However, access is prone to developing complications that can limit or halt its function. The most common problem is stenosis, a significant narrowing of the blood vessel, often occurring near the connection to the native vein.
Stenosis is caused by a buildup of scar tissue (neointimal hyperplasia), which progressively restricts the blood flow pathway. If left unchecked, restricted flow creates a high risk of thrombosis, or complete clotting, resulting in sudden access failure. The justification for the surveillance procedure coded by CPT 93970 is the early detection of these flow-limiting stenoses.
Identifying stenosis before failure prevents emergency interventions and hospitalizations. Maintaining patent access also reduces the need for temporary central venous catheters, which carry a higher risk of infection. Early detection allows for timely, less invasive procedures, such as angioplasty, to correct the narrowing and prolong the functional life of the access.
The Duplex Scan Procedure
The duplex scan is a non-invasive procedure performed in an outpatient setting by a registered vascular technologist. The patient is positioned comfortably, and a water-based gel is applied to the skin over the access to facilitate the transmission of sound waves.
A handheld transducer is gently moved along the entire length of the access, from the arterial inflow to the venous outflow. The transducer emits high-frequency sound waves that bounce off blood cells and vessel walls, creating echoes processed into images. The color Doppler feature overlays the structural image with color coding to represent the direction and velocity of blood flow.
The technologist systematically measures specific parameters throughout the access pathway. These measurements include vessel diameter, volume flow rate, and peak systolic and end-diastolic blood flow velocities at multiple points. The presence of turbulent flow, which indicates an underlying restriction, is also noted. The examination is painless and does not involve radiation exposure.
Interpreting the Clinical Findings
The goal of the duplex scan is to provide the interpreting physician with detailed, quantifiable data about the access’s current function. A key finding is significant stenosis, identified by a dramatic increase in blood flow velocity through the narrowed segment. Stenosis is often considered hemodynamically significant if the peak systolic velocity is substantially elevated compared to the upstream segment.
The physician also assesses the volume flow rate, measured in milliliters per minute, because a low flow rate strongly predicts imminent thrombosis. A flow rate below a certain threshold, such as 500 mL/min, can correlate with access failure within months. Conversely, a complete blockage (thrombosis) is indicated by the absence of color flow and the visualization of clotted blood within the vessel lumen.
These quantified findings dictate the next steps in patient care. If the scan identifies a severe stenosis (e.g., greater than 50% diameter reduction) or a significantly reduced flow rate, the patient is promptly referred for a corrective procedure. Interventions may include percutaneous transluminal angioplasty, which uses a balloon to open the narrowed segment, or a thrombectomy to remove a clot. The duplex scan results serve as the roadmap for preemptive maintenance, ensuring the continued viability of the vascular access.