Association of the Fibrosis-4 index with thyroid nodule prevalence in women: a cross-sectional study

Background The relationship between liver-related metabolic markers and thyroid nodules (TNs) has attracted increasing interest. However, whether the Fibrosis-4 (FIB-4) index is independently associated with TN prevalence in women, particularly after accounting for the age embedded in the score, remains unclear. We investigated the association between FIB-4 and prevalent TNs in a female health-check cohort and assessed its robustness in age-stratified and age-adjusted analyses.Methods We conducted a cross-sectional analysis of 695 women from a health examination cohort at The Second Affiliated Hospital of Anhui Medical University. TNs were defined as ultrasound-detected thyroid nodules. Multivariable logistic regression estimated odds ratios (ORs) and 95% confidence intervals (CIs) for prevalent TNs according to standardized FIB-4 levels. Prespecified age-stratified analyses were performed for women aged ≤ 60 years and > 60 years. Within each age stratum, an additional model adjusted for continuous age. Age-adjusted within-stratum results were considered the main basis for interpretation.Results In the full female cohort, the association between FIB-4 and prevalent TNs was attenuated after additional adjustment for continuous age (OR 1.104, 95% CI 0.822-1.484; P = 0.511). In age-adjusted within-stratum analyses, FIB-4 was not significantly associated with prevalent TNs in either women aged ≤ 60 years (OR 1.211, 95% CI 0.837-1.751; P = 0.310) or women aged > 60 years (OR 0.567, 95% CI 0.289-1.113; P = 0.099). The corresponding base model estimates before additional continuous-age adjustment were OR 1.564 (95% CI 1.086-2.253; P = 0.016) and OR 0.576 (95% CI 0.278-1.193; P = 0.138), respectively. The interaction between FIB-4 and age group was not statistically significant (P for interaction = 0.239).Conclusions After additional adjustment for continuous age within age strata, the association between FIB-4 and prevalent thyroid nodules in women was attenuated and no longer statistically significant. These findings suggest that the apparent relationship between FIB-4 and TN prevalence in this health-check population may be substantially influenced by age handling and should be interpreted cautiously.Clinical trial number Not applicable.