Background: A major problem with the University of Pennsylvania Smell Identification Test (UPSIT) is its poor sensitivity for malingering detection in a group of people familiar with the test mechanism. This study aimed to evaluate the modification of UPSIT to detect anosmia malingering.
Methods: This was a pilot experimental study conducted in 2019 in Tehran. The participants were 60 healthy subjects classified into two groups of 30 people. The first group was requested to deliberately feign a negative result on the Iranian version of UPSIT, Iran Smell Identification Test (ISIT) (malingering group). The second group consisted of participants, who did not scratch the odorant part of ISIT during the tests (anosmia group). ISIT was modified in two steps. At each step, one incorrect option was deleted from the available choices. The number of each group’s answers, altered away from the correct choice, was then calculated and compared.
Results: The coached malingering group participants were able to feign anosmia in the original ISIT exam. In the modified ISIT, the number of answers changed from correct to wrong during the second stage (from three available choices to two choices) was significantly higher in the anosmia group (P<0.001). In the ROC analysis, the area under the curve was 0.92 (P<0.001). The cut-off of 4.5 for this test showed 93% sensitivity, 82% specificity, and 90% PPV and NPV.
Conclusion: The ISIT is not capable of detecting malingering in the coached participants, yet by deleting the choices step-by-step, the sensitivity and specificity of the test increased.