The assessment of qualitative olfactory dysfunction in COVID-19 patients: a systematic review of tools and their content validity

Abstract

BackgroundThere is a lack of overview of the tools used to assess qualitative olfactory dysfunction, including parosmia and phantosmia, following COVID-19 illness. This could have an impact on the diagnosis and treatment offered to patients. Additionally, the formulations of symptoms are inconsistent and often unclear, and consensus around the wording of questions and responses is needed.Aim of studyThe aim of this systematic review is to provide an overview of tools used to assess qualitative olfactory dysfunction after COVID-19, in addition to addressing the content validity (i.e., item and response formulations) of these tools.MethodsMEDLINE, Web of Science, and EMBASE were searched 5th of August 2022 and updated on the 25th of April 2023 to identify studies that assess qualitative olfactory dysfunction in COVID-19 patients. Primary outcomes were the tool used (i.e., questionnaire or objective test) and item and response formulations. Secondary outcomes included psychometric properties, study design, and demographic variables.ResultsThe assessment of qualitative olfactory dysfunction is characterized by heterogeneity, inconsistency, and lack of validated tools to determine the presence and degree of symptoms. Several tools with overlapping and distinct features were identified in this review, of which some were thorough and detailed, while others were merely assessing the presence of symptoms as a binary measure. Item and response formulations are also inconsistent and often used interchangeably, which may lead to confusion, incorrect diagnoses, and inappropriate methods for solving the problem.ConclusionsThere is an unmet need for a reliable and validated tool for assessing qualitative olfactory dysfunction, preferably one that also captures quantitative olfactory issues (i.e., loss of smell), to ensure time-effective and specific assessment of the ability to smell. A consensus around the formulation of items and response options is also important to increase the understanding of the problem, both for clinicians, researchers, and the patient, and ultimately to provide the appropriate diagnosis and treatment.Registration and protocolThe URL is https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=351621. A preregistered protocol was submitted and accepted (12.09.22) in the International prospective register of systematic reviews (PROSPERO) with the registration number CRD42022351621.

Updated Clinical Practice Guidelines for the Diagnosis and Management of Long COVID

“…Current research on the assessment of olfactory and gustatory disorders in COVID-19 patients remains insufficient. In a systematic literature review conducted by Annelin et al focusing on qualitative olfactory function assessment, 72 studies were analyzed [ 93 ]. Of these, only four objective assessment tools were used for olfactory function: the Chemosensory Perception Test, Yale Jiffy Smell Identification Test, SCENTinel 1.1, and the Sniffin' Sticks Test.…”

“…Of these, only four objective assessment tools were used for olfactory function: the Chemosensory Perception Test, Yale Jiffy Smell Identification Test, SCENTinel 1.1, and the Sniffin' Sticks Test. Conversely, subjective assessment tools such as the National Health and Nutrition Examination Survey, Questionnaire of Olfactory Disorders, and the Global Consortium for Chemosensory Research questionnaire were more commonly employed [ 93 ]. While objective assessments have the advantage of providing consistent data, they are limited in their inability to evaluate phantosmia, the sensation of non-existent odors.…”

The Molecular Basis of Olfactory Dysfunction in COVID-19 and Long COVID

“…Other factors contributing to the wide range of reported prevalence rates (from 5 to 88%) included patients' age, gender, ethnicity, and the virus variant [41][42][43]. The evaluation of questionnaires and patients' self-reports highlighted the significant role and high prevalence (11-23.4% in various studies) of persistent parosmia, a distorted perception of odors, several months after COVID-19 [40,[44][45][46][47].…”

“…In addition, it should be noted that having a (pre-COVID) baseline would be necessary for the objective evaluation of OD, but this is generally unavailable. For the evaluation of qualitative OD such as parosmia (an altered perception of odors) or phantosmia (an olfactory hallucination that causes the detection of smells that are not actually present in the environment) leading to a distorted perception of odors, several psychophysical testing tools, such as SCENTinel 1.1, the Sniffin' Sticks parosmia test (SSParoT), or Yale Jiffy are available, but only partly validated and still not widely used in everyday practice [40,45].…”