The predictive value of ventilation-perfusion scanning for the diagnosis of pulmonary embolism in patients with impaired renal function.

BACKGROUND: Computed tomography pulmonary angiography (CTPA) is considered the method of choice for diagnosing pulmonary embolism (PE). In most patients with impaired renal function, ventilation-perfusion (V/Q) scanning is the preferred modality.
OBJECTIVES: To evaluate the predictive value of V/Q scanning in patients with impaired renal function.
METHODS: We assessed all patients with impaired renal function who underwent V/Q scanning. The patients studied included those who also had CTPA (group 1) and those who did not (group 2). We recorded the results ofV/Q scanning, chest X-rays, CTPA, D-dimer levels, ultrasound of deep veins, and clinical probability for PE (Wells' score) in group 1. CTPA results were considered true results. Anticoagulant treatment was documented in all the patients.
RESULTS: Of the 45 patients in group 1, 12 (22%) had positive CTPA for PE. The positive predictive value (PPV) for patients with high probability results on V/Q scanning for PE was 30%. Restricting results to D-dimer levels > or = 1000 ng/ml added little to this value. Restricting results to Wells' score > or = 7 resulted in 72% PPV. The negative predictive values for low or moderate probability were approximately 79% and approximately 67% respectively Of the 95 patients in group 2, all those with high probability for PE were treated with anticoagulants.
CONCLUSIONS: Patients with impaired renal function and high probability for PE on V/Q scanning had very low PPV for PE. Due to the lack of CTPA studies, patients with high probability for PE on V/Q scanning were treated with anticoagulants.