Bone Metabolism Biomarkers as Potential Diagnostic Tools for Non-Alcoholic Fatty Liver Disease: Findings from a Case–Control Study

Non-alcoholic fatty liver disease (NAFLD) is increasingly recognized as a systemic condition affecting extrahepatic organs, including bone. Alterations in bone metabolism may occur early in the disease course. This study aimed to evaluate the diagnostic and prognostic relevance of selected bone metabolism markers osteocalcin, C-terminal telopeptide of type I collagen (CTX), and fibroblast growth factor 23 (FGF23) in NAFLD patients. A case-control study was conducted involving 45 NAFLD patients and 45 age-, sex-, and body mass index-matched healthy controls. Serum levels of osteocalcin, CTX, and FGF23 were measured using ELISA. The degree of hepatic steatosis was assessed by ultrasonography, while fibrosis risk was evaluated using the FIB-4 index. Statistical analyses included ROC curve analysis, correlation, and group comparisons. NAFLD patients showed significantly lower osteocalcin and higher CTX and FGF23 compared with controls (p < 0.001). ROC analysis revealed strong diagnostic accuracy for osteocalcin (AUC = 0.976, sensitivity 97.8%, specificity 86.7%), CTX (AUC = 0.894, sensitivity 91.1%, specificity 93.3%), and FGF23 (AUC = 0.922, sensitivity 97.8%, specificity 84.4%). While these markers correlated with liver enzymes and fibrosis indices, they were not significantly associated with steatosis or fibrosis severity. In conclusion, alterations in osteocalcin, CTX, and FGF23 suggest a metabolic link between liver and bone. These markers may serve as promising non-invasive diagnostic biomarkers for NAFLD, but larger studies with histological validation are needed.