How many and which odor identification items are needed to establish normal olfactory function?

Abstract

The establishment of normal olfactory function by means of a simple and reliable test is one method that could minimize olfactory test procedures in the clinic. This retrospective study analyzed the identification of 16 odors by 613 subjects (aged 18-96 years, 266 men) as a part of a complex olfactory test battery by which 183, 251, and 179 subjects were diagnosed with anosmia, hyposmia, or normosmia, respectively. Cinnamon was identified as the best scoring odor, that is, identified correctly by most normosmic subjects, but identified correctly by the fewest anosmic patients. An exact calculation of the optimum number of items needed for a diagnosis of normosmia resulted in 1 single odor identification item as being sufficient. The inclusion of more items is solely determined by the acceptable proportion of chance, which in a 4-alternative forced choice paradigm is only 1.6% with 3 odors. A proposed screening test using cinnamon, fish odor, and banana established normosmia at a sensitivity of 80.4% and a specificity of 84.3% and a negative predictive value of 91.3%.A positive test result reliably establishes normosmia providing a confidence basis to terminate olfactory assessments following the application of only 3 odor identification items.