4. Discussion
In this study, we developed and tested a frailty index constructed from physiological parameters (routine laboratory tests and anthropometric measures). This class of frailty indices is gaining popularity as an alternative to clinical FIs. The key distinction between clinical FI and FI-Lab is that the latter is based entirely on biochemical markers/physiological parameters; hence it is believed to represent the burden of preclinical or subclinical deficits [18]. Subclinical deficits can be thought of as systemic, organ-level dysregulation that occurs as a direct result of molecular or cellular level damage (e.g., oxidative stress and telomere attrition) and in turn leads to “macroscopic” (clinically evident) functional deficits and impairments such as disease, weakness, limited mobility, cognitive changes, and sensory loss [4]. In some sense, the subclinical dysregulation measured by FI-Lab provides an intermediate link within cellular-level damage that eventually scales up to clinically detectable impairments/deficits [17]. We therefore believe that WTC FI-Lab has the potential to identify frailty in its early stages among our cohort. In accordance with this, we used a relatively low age cutoff in the selection of the sample for this study. As a result, our study cohort is younger (median age of 51) than those in other frailty studies, which often focus on the elderly. The rationale behind this sample selection choice is that the development of WTC FI-Lab and other biomarker-based tools for biological age assessment will allow screening of those at risk of advanced frailty endpoints. There is a growing evidence that frailty may be modifiable/reversible, especially in the early stages [38] preceding the onset of more advanced symptoms. This calls for the development of valid tools for screening at-risk individuals.
