Background: In patients with suspected pulmonary embolism (PE), the literature suggests the overuse of computerized tomography pulmonary angiography (CTPA) and underuse of clinical decision rules before imaging request. This study determined the potential for avoidable CTPA using the modified Wells score (mWS) and D-dimer assay in patients with suspected PE. Methods: This hospital-based retrospective study analyzed the clinical data of 661 consecutive patients with suspected PE who underwent CTPA in the emergency department of a tertiary hospital for the use of a clinical prediction rule (mWS) and D-dimer assay. The score was calculated retrospectively from the available data in the files of patients who did not have a documented clinical prediction rule. Overuse (avoidable) CTPA was defined as D-dimer negativity and PE unlikely for this study. Results: Of 661 patients’ data examined, clinical prediction rules were documented in 15 (2.3%).In total, 422 patients (63.8%) had required information on modified Wells criteria and D-dimer assays and were included for further analysis. PE on CTPA was present in 22 (5.21%) of PE unlikely (mWS ≤4) and 1 (0.24%) of D-dimer negative patients. Thirty patients (7.11%) met the avoidable CTPA (DD negative+PE unlikely) criteria, and it was significantly associated with dyspnea. The value of sensitivity of avoidable CTPA was 100%, whereas the positive predictive value was 90.3%. Conclusion Underutilization of clinical prediction rules before prescribing CTPA is common in emergency departments. Therefore, a mandatory policy should be implemented regarding the evaluation of avoidable CTPA imaging to reduce CTPA overuse.