A recent study from our group showed the crucial role of osteoimmunological biomarkers in the evaluation of COVID-19 [29], describing a significant role for the RANKL/OPG ratio (the osteoimmunological markers of bone resorption), the bone fragility marker FGF23, and the interaction with two inflammatory markers: the primary cytokine IL-6 and the soluble maker sRAGE. Here, FGF23 is linked to COVID-19.