Immune fitness (i.e., adequate functioning of the immune system) is essential to maintain health, prevent and resolve disease, and improve quality of life. This article provides an overview of how to assess immune fitness. It discusses how a single-item rating scale can be used to assess immune fitness. The scale can be used in conjunction with a single "yes" or "no" question asking whether the individual is experiencing reduced immune fitness. Retrospective assessments can be complemented with the Immune Status Questionnaire (ISQ) to provide more insight into the type and frequency of experiencing specific immune-related complaints. Momentary assessments of immune fitness can be complemented with biomarker measurements in body fluids. As individuals may be unaware of systemic inflammation (e.g., biomarker concentrations outside the normal range), it remains critical to combine immune fitness assessments with biomarker measurements of immune functioning.
Keywords: ISQ; assessment; biomarkers; immune fitness; immune functioning; single-item scale.