This study aimed to propose an operational definition of late-onset hypogonadism (LOH) that incorporates both clinical symptoms and serum testosterone measurements to evaluate the prevalence of LOH in aging males in China. A population-based sample of 6296 men aged 40 years–79 years old was enrolled from six representative provinces in China. Serum total testosterone (TT), sex hormone-binding globulin (SHBG), and luteinizing hormone (LH) were measured and free testosterone (cFT) was calculated. The Aging Males' Symptoms (AMS) scale was used to evaluate the LOH symptoms. Finally, 5078 men were included in this analysis. The TT levels did not decrease with age (P = 0.59), and had no relationship with AMS symptoms (P = 0.87 for AMS total score, P = 0.74 for ≥ 3 sexual symptoms). The cFT levels decreased significantly with age (P < 0.01) and showed a negative association with the presence of ≥ 3 sexual symptoms (P = 0.03). The overall estimated prevalence of LOH was 7.8% (395/5078) if a cFT level <210 pmol l−1 combined with the presence of ≥ 3 sexual symptoms was used as the criterion of LOH. Among them, 26.1% (103/395) and 73.9% (292/395) had primary and secondary hypogonadism, respectively. After adjustment for confounding factors, primary and secondary hypogonadism was positively related to age and comorbidities. Body mass index was an independent risk factor for secondary hypogonadism. The results suggest that the AMS total score is not an appropriate indicator for decreased testosterone, and that the cFT level is more reliable than TT for LOH diagnosis. Secondary hypogonadism is the most common form of LOH.

Keywords: Aging Males' Symptoms; calculated free testosterone; late-onset hypogonadism; middle-aged and elderly male; total testosterone

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