Successful and Safe Implementation of a Trinary Interpretation and Reporting Strategy for V/Q Lung Scintigraphy

Abstract

For the past 4 decades, ventilation-perfusion (V/Q) scan interpretation for pulmonary embolism (PE) was performed using probability-based assessments, which were neither well-received nor well-understood by many clinicians. Recently, we combined normal, very low probability, and low-probability interpretations in emergency department patients and found a false-negative (FN) rate of 1.2% on follow-up. Afterward, we transitioned to a new trinary interpretative strategy: no PE, PE present, and nondiagnostic. In this series, we compared the outcomes of the traditional and trinary interpretative strategies. We retrospectively identified all patients undergoing V/Q scans for the 1 year straddling the shift in interpretive strategy, with traditional interpretation being used between September 18, 2008, and March 17, 2009, and trinary interpretation being used between March 18, 2009, and September 17, 2009. A FN study was defined as development of deep vein thrombosis or PE within 3 months after a negative baseline evaluation. The traditional interpretation group included 208 male patients (27%) and 570 female patients (73%), with a mean age (±SD) of 50.9 ± 18.4 years. These interpretations (n = 778) were high probability in 4.9% (38), intermediate probability in 5% (39), low probability in 59.5% (463), very low probability in 17.2% (134), and normal in 13.4% (104). The trinary interpretation group included 181 male patients (27%) and 483 female patients (73%), with a mean age of 50.0 ± 18.5 years. These interpretations (664) were positive in 8.4% (56), negative in 88.1% (585), and nondiagnostic in 3.5% (23). The FN rate was 1.14% (8/701; 7 deep vein thrombosis and 1 PE) for pooled normal, very low probability, and low probability in traditional interpretations versus 1.5% (9/585, 5 deep vein thrombosis and 4 PE) in trinary interpretations (P = 0.63). The individual FN rates for the normal, very low probability, and low-probability groups were 0.0%, 0.75%, and 1.51%, respectively (P = 0.36 for normal vs. low probability). Pediatric subgroup analysis showed 19 traditional interpretations: 5.3% high (1); 0 intermediate; and 94.7% (18) low probability, very low probability, and normal. 20 trinary interpretations were positive in 10% (2), nondiagnostic in 5% (1), and negative in 85% (17), with no FNs using either strategy. A simplified trinary interpretation strategy for V/Q lung scintigraphy provides outcomes similar to traditional probability assessments and facilitates clear communication.