Advancing Smell Disorder Diagnostics: A Comparative Review of Portable Test Kits and Self-Reported Tools

Olfactory Dysfunction (OD) is a prevalent yet underdiagnosed sensory disorder with profound implications for quality of life and for the early detection of neurodegenerative diseases such as Parkinson's and Alzheimer's. Beyond its sensory role, OD has emerged as an early, noninvasive biomarker of neurodegenerative pathology, often preceding measurable cognitive decline in Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI). Quantitative smell loss correlates with pathological changes in the olfactory bulb and entorhinal cortex, highlighting its diagnostic potential for early screening and longitudinal monitoring.

Traditional diagnostic tools, though validated, often require specialized personnel, laboratory infrastructure, and extended testing time, limiting accessibility. This review critically examines recent innovations in the detection of olfactory dysfunction, focusing on portable, user-friendly smell test kits and their comparative performance with self-reported tools such as the Mini Olfactory Questionnaire (Self-MOQ) and 4-CAST. We synthesize evidence on diagnostic reliability, usability, and cultural adaptability, evaluating how these methods align with emerging needs in Alzheimer's and dementia research.

Portable kits such as PT-Smell and SSomix demonstrate high diagnostic precision and cultural adaptability, while self-administered and self-report tools enable scalable deployment in memory clinics and community screening programs. Within Alzheimer's research, these approaches present practical solutions for early identification of sensory biomarkers linked to cognitive decline.

To optimize diagnostic integration, a two-step framework is proposed: first-line screening with self-administered tools such as Self-MOQ or 4-CAST, followed by confirmatory psychophysical testing with portable kits such as PT-Smell or SSomix. This tiered model supports early AD and MCI detection, enhances accessibility, and promotes digital health integration for widespread olfactory monitoring.