Observational associations of the residual cholesterol-to-HDL-C ratio as a metabolic correlate of low testosterone in adult men: Insights from NHANES 2011–2016

Testosterone deficiency (TD) is a prevalent and underdiagnosed condition associated with adverse metabolic and cardiovascular outcomes. The remnant cholesterol to high-density lipoprotein cholesterol ratio (RC/HDL-C) has emerged as a novel lipid marker reflecting both atherogenic burden and metabolic dysfunction. However, its relationship with testosterone levels remains unclear. We analyzed data from 2782 adult men aged ≥ 20 years from the National Health and Nutrition Examination Survey (NHANES) 2011–2016. TD was defined as total testosterone (TT) < 300 ng/dL. RC/HDL-C was calculated as (total cholesterol − LDL-C − HDL-C)/HDL-C. Multivariable survey-weighted linear and logistic regression models were used to evaluate the association between RC/HDL-C and TT levels and TD risk. Generalized additive models were applied to assess nonlinear relationships, and receiver operating characteristic (ROC) curve analysis was performed to evaluate discriminative performance. Higher RC/HDL-C was significantly associated with lower TT and increased odds of TD. In the fully adjusted model, each unit increase in RC/HDL-C was associated with a 52.25 ng/dL decrease in TT (β = –52.25, 95% CI:–74.64 to–29.85, P < .0001), and 81% higher odds of TD (OR = 1.81, 95% CI: 1.36 to 2.41, P < .001). Compared to the lowest RC/HDL-C quartile, individuals in the highest quartile had significantly lower TT levels (β = –74.47, 95% CI:–107.81 to–41.13) and higher TD risk (OR = 2.25, 95% CI: 1.24 to 4.07). Subgroup analyses confirmed consistent associations across age, BMI, metabolic status, and lifestyle factors. Smooth curve fitting revealed monotonic relationships. The RC/HDL-C ratio demonstrated superior discriminatory ability for TD (AUC = 0.647) compared to RC (AUC = 0.633) and HDL-C (AUC = 0.619). High RC/HDL-C ratio is associated with a higher likelihood of TD, though the cross-sectional nature of this study limits the ability to establish causality.