Association of blood biomarkers with frailty–A mapping review

Frailty describes a geriatric syndrome characterized by an increased vulnerability. Although a variety of potential blood-based biomarkers have been discussed for its characterization, a reliable protocol considering blood-based biomarkers for this purpose is still missing. However, a comprehensive overview on these biomarkers is necessary to understand potential molecular pathways to frailty. We, therefore, performed a mapping review to identify those blood-based biomarkers most consistently associated with frailty in community-dwelling older adults as well as possible analytical gaps according to the available literature. A proposed weighted correlation index (CI) describing the direction and consistency of the association considering the number of available publications as well as the size of the study populations was calculated for each biomarker. Overall, 72 manuscripts were critically reviewed reporting on a total of 82 biomarkers. The most consistent positive association with at least 3 articles addressing the respective biomarker in unadjusted and fully adjusted models was shown for interleukin 6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), neopterin, white blood cells count, glycated hemoglobin A1c (HbA1c) and sex hormone binding-globuline (SHBG) with a CI ≥ 0.7, while for negative association hemoglobin, 25-hydroxy vitamin D, free testosterone in men and albumin with a CI ≤ -0.7 were identified.