Nasal Mucociliary Clearance Assessment: Historical Evolution, Methodological Approaches, and the Role of Activated Charcoal as a Visible Marker

Abstract

Nasal mucociliary clearance assessment has evolved over more than a century through a continuous search for methods that balance physiological relevance, clinical practicality, objectivity, cost, reproducibility, and patient tolerance. Early approaches were based on direct observation and dye-based techniques, followed by saccharin transit time testing, visible particle methods, charcoal-based tracers, radiolabeled particle techniques, scintigraphic assessment, and modern specialized tests of ciliary function. The available methods differ substantially in their principles and practical applications. Saccharin transit time testing became widely used because of its simplicity, low cost, and accessibility, but its endpoint depends on subjective taste perception and patient reporting. Dye-based and visible particle techniques attempted to make mucociliary transport more directly observable, whereas radiolabeled and scintigraphic methods introduced greater objectivity at the cost of technical complexity and limited routine applicability. Modern investigations such as ciliary beat frequency analysis, high-speed video microscopy, nasal nitric oxide measurement, transmission electron microscopy, immunofluorescence, and genetic testing are essential in selected diagnostic contexts, particularly in primary ciliary dyskinesia, but they are not equivalent to direct nasal transport-time assessment. Activated charcoal should be understood within this broader historical and methodological evolution. It is not a newly introduced method and should not be presented as a universal replacement for established techniques. Rather, it is a topical, low-cost, dark, visible marker that may permit examiner-observed recognition of the endpoint. However, the additional value of standardized endoscopic control requires prospective comparative validation. This review examines the historical development of nasal mucociliary clearance assessment, compares the major methodological approaches, and critically discusses the potential methodological role of activated charcoal as a visible marker, particularly in pediatric otorhinolaryngology.