Olfactory Assessment for Affordable Parkinson Evaluation: Specificity, Enrichment, and the Cost of Follow-Up

Abstract Olfactory assessment is attractive as a comparatively low-burden component of Parkinson evaluation, but an inexpensive first test does not guarantee an affordable or clinically informative pathway. Smell loss has multiple causes, and the value of an abnormal result depends on the population, threshold, and subsequent assessment. This article combines a targeted synthesis of established and recent primary evidence with a reproducible hypothetical analysis of three olfactory operating points. Among 10,000 people with a specified target-condition prevalence of 1%, a sensitivity-oriented operating point with 90% sensitivity and 60% specificity generates 4,050 positive results, of which 90 are true positives. A more restrictive operating point with 60% sensitivity and 90% specificity generates 1,050 positives, of which 60 are true positives. Positive predictive values are 2.22% and 5.71%, respectively; neither supports standalone diagnosis. At the intermediate operating point, 80% sensitivity and specificity generate 2,060 follow-up assessments. An illustrative provider cost of five resource units for olfaction and sixty for follow-up produces 173,600 total units, while patient payments depend separately on the financing arrangement. A specificity-mixture analysis shows that applying a 90% specificity estimate to a population containing substantial non-Parkinson olfactory impairment can underestimate follow-up demand by 1,188 assessments. Recent abbreviated-test research supports investigation of shorter assessments, while recent work comparing Parkinson-related and non-Parkinson hyposmia cautions against assuming disease-specific odor patterns. The practical requirement is a staged pathway with appropriate comparison groups, valid local norms, transparent follow-up costs, and an alternative clinical route for persistent concerns. 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