Diagnostic yield of repeat CT pulmonary angiography after a negative examination in the emergency department

Purpose Although repeat CT pulmonary angiography (CTPA) after a negative index examination in the emergency department (ED) is common, its diagnostic utility remains uncertain. This study aimed to determine the incidence and diagnostic yield of repeat CTPA after a negative index examination in the ED. Methods This retrospective cohort study included adults undergoing CTPA across three EDs at our center from 2016 to 2017. CTPA results were classified as positive, negative, or other (equivocal or negative with reported limitations) based on radiology reports. Patients with a negative index CTPA were followed for two years to identify repeat examinations. Diagnostic yield of repeat CTPA at 1 month, 1 year, and 2 years was compared with that of the index examination using a likelihood ratio test for nested proportions. Results Among 3,112 patients (median age, 60.1 years; 59.1% women), 331 (10.6%) had a positive index CTPA. Of 2,412 patients with a negative index examination, 297 (12.3%) underwent repeat CTPA within 2 years, including 202 (8.4%) performed in our ED. The diagnostic yield of repeat CTPA performed in our ED was lower than that of the index examination: 3.8% (1/26; p = 0.20) at 1 month, 6.0% (9/150; p = 0.051) at 1 year, and 6.4% (13/202; p = 0.04) at 2 years. Conclusion Repeat CTPA after a negative examination demonstrated a lower diagnostic yield than initial imaging, highlighting an opportunity for more selective use of repeat CTPA guided by clinical pretest probability.