A Clinically Meaningful Interpretation of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) Scintigraphic Data

Abstract

Pulmonary embolism (PE) is a common condition associated with significant morbidity and mortality. Diagnostic test characteristics reported in terms of sensitivity and specificity are difficult to translate at the clinical level. More relevant measures are likelihood ratios (LRs), which can convert a pretest into a posttest probability. The aim of our study was to calculate the LRs and posttest probabilities for multiple-level test result for ventilation/perfusion (V/Q) lung scintigraphy and for perfusion scintigraphy combined with chest radiography using modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II and the Prospective Investigative Study of Pulmonary Embolism Diagnosis (PISAPED) criteria for each clinical probability level for the most commonly used clinical prediction rules (CPR) using the PIOPED data. PE pretest probability was estimated for the most commonly used CPRs (Wells, Geneva, Miniati, and Charlotte) at each clinical probability level (two-, three-, and four-level). Multiple-level LRs (high, indeterminate, low, very low probability, and normal) and the positive, indeterminate, and negative results for V/Q scintigraphy, and the positive, indeterminate, and negative results for perfusion scintigraphy were generated and used to calculate posttest probabilities based on the sensitivity and specificity data from PIOPED for each clinical probability level (low, intermediate, and high) for each CPR. Nomograms were also created. The LRs for a positive V/Q and perfusion scintigraphy test using modified PIOPED II and PISAPED criteria were 20.6, 11, and 23.7, and for a negative test result were 0.15, 0.16, and 0.2, respectively. In the three-level Wells score, the posttest probability for an initial low clinical probability PE for a positive, indeterminate, and negative test result, respectively, for V/Q scintigraphy is 56, 5, and 0.9; for perfusion scintigraphy with modified PIOPED 40, 7, and 0.9, and with PISAPED 59, not available (N/A), and 1.2; for an initial moderate clinical probability PE for V/Q scintigraphy 86, .22, and 4; for perfusion scintigraphy with modified PIOPED 77, 26, and 5, and with PISAPED 88, N/A, and 6; for an initial high clinical probability of PE for V/Q scintigraphy 95, 48, and 13; and for perfusion scintigraphy with modified PIOPED 92, 53, and 13, and with PISAPED 96, N/A, and 16. With LRs >10, a positive test result for V/Q and perfusion scintigraphy can confirm the presence of PE. Only a normal test result has low enough LR to exclude PE.