Comparative study of ventilation/perfusion SPECT and blood D-dimer test for diagnosis of low probability pulmonary embolism

Objective: To compare the diagnostic efficiency of V/Q SPECT and blood D-dimer test in patients with low probability (Wells score < 2) of PE. Methods: From January 2010 to August 2013, 95 patients with low probability of PE were recruited from four hospitals in Beijing. The patients underwent V/Q SPECT and blood D-dimer test on the same day. The European Association of Nuclear Medicine guidelines (2009) was used as the evaluation criteria for V/Q SPECT imaging. The results of V/Q SPECT were classified as definite PE, suspected PE and no PE. All patients were followed clinically for at least six months. Final diagnosis was decided based on the results of multiple imaging modalities, laboratory tests, clinical data and follow-up. The diagnostic efficiency of V/Q SPECT was calculated and compared with those of blood D-dimer test. χ² test was used for data analysis. Results: PE was confirmed in 31 patients, and excluded in 64 patients. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value of V/Q SPECT were 93.3%(28/30; 95% CI: 84.4%-100%), 91.9%(57/62; 95% CI: 85.1%-98.7%), 92.4%(85/92; 95% CI: 87.0%-97.8%), 84.8%(28/33; 95% CI: 83.6%-86.0%), 96.6%(57/59;95% CI: 92.0%-100%) respectively, while those of blood D-dimer test were 36.7% (11/30; 95% CI: 19.5%-53.9%), 79.0%(49/62; 95% CI: 68.9%-89.1%), 65.2%(60/92;95% CI: 55.5%-14.9%), 45.8% (11/24; 95% CI: 25.7%-65.7%), 72.1%(49/68; 95% CI: 61.4%-82.8%) respectively. The sensitivity (χ² = 21.2), specificity (χ² = 13.8), accuracy (χ² = 203), positive predictive value (χ² = 9.8) and negative predictive value (χ² = 4.2) of V/Q SPECT were significantly higher than those of blood D-dimer test (all P < 0.05). Conclusion: The diagnostic efficiency of V/Q SPECT imaging may superior to blood D-dimer test in the diagnosis of low probability PE. (authors)