Question: Should I use an unlisted code or +93571 for iFR (Instant Wave-Free Ratio)? California Subscriber Answer: You should use +93571 (Intravascular Doppler velocity and/or pressure derived coronary flow reserve measurement [coronary vessel or graft] during coronary angiography including pharmacologically induced stress; initial vessel [List separately in addition to code for primary procedure]). For each vessel after the first, use +93572 (...each additional vessel [List separately in addition to code for primary procedure]). You should append modifier 52 (Reduced services) because while iFR largely meets the service described in the code descriptors, it does not involve the "pharmacologically induced stress" listed in +93571 and +93572, according to the December 2015 CPT® Assistant. The American College of Cardiology and the Society for Cardiovascular Angiography and Interventions make the same recommendation in a letter posted at www.volcanocorp.com/products/pdf-files/ACC-SCAI-Recommendation-Letter-for-iFR-CPT-Coding.pdf.