In a diagnostic test study the validity of three serodiagnostic test was compared in patients with liver echinococcosis.

Background and Objective: To determine the efficacy of immunoprecipitation (DD5), enzyme immunoanalysis (ELISA-IgG), and immunoelectrotransference or Western blot (WB) in patients with liver echinococcosis (LE) used separately, in parallel and in series.
Methods: Diagnostic test study. DD5, ELISA-IgG, and WB were applied in 75 patients with LE and 75 with cholelithiasis. Surgery was considered a reference standard. The sample size was calculated assuming a 99% confidence interval (99% CI), expected sensitivity (S) of 90% and a worst result of 80%; expected specificity (SP) of 95% and a worst result of 85%. S, SP, and predictive values (PPV and NPV) were calculated.
Results: The best S was verified with ELISA-IgG and WB (82.7%) and the best SP with DD5 (94.7%). DD5 presented a better PPV (92.9%) and WB a better NPV (83.5%). When applying the tests in parallel, the best S was obtained from the combination of DD5 and WB (82.7%); and the best SP, PPV and NPV with ELISA-IgG and WB (88.0%, 87.3%, and 83.5%, respectively).
Conclusions: DD5 appears as the most specific test and as having greater PPV; ELISA-IgG and WB are more sensitive. The combined use of these tests does not improve diagnosis validity.