Post-test probability for pulmonary embolism after ventilation-perfusion scan assessed by nuclear medicine physicians

The objective of this prospective study was to compare assessments of pre- and post-ventilation-perfusion (V/Q) scan probabilities for pulmonary embolism (PE) by the nuclear medicine physician and the referring physician.

Seventy-nine patients (41 females, 38 males, mean age 49 years) referred for V/Q scans over a period of 6 months and suspected of PE were included in the study. The pre-test likelihood was determined independently by a consultant nuclear physician and a referring physician prior to the V/Q scan. The scan was performed according to a standard protocol using 8 view technetium-99m diethylenetriamine pentaacetic acid aerosol ventilation study followed by a technetium-99m macroaggregated albumin perfusion study. The scan was interpreted according to prospective investigation of pulmonary embolism diagnosis criteria. The post-scan probability was calculated. The probability of PE was quoted as low, intermediate and high. Agreement or disagreement in assessing the pre- and post-scan probability was classified according to the degree of difference (no difference: 0; minor difference: 1, and major difference: 2 grades).

The agreement between the nuclear medicine and referring physicians on clinical probability of PE was moderate (63%) before the scan and good (90%) after the scan. The disagreement in assessing the clinical probability between the referring physician and the nuclear medicine physician was predominantly minor. Only 5 and 1% of the disagreement was major in pre-scan and post-scan probabilities, respectively.

The data show that nuclear medicine physicians can use the assessment of pre-scan clinical likelihood to determine the post-scan probability of PE.