Although, in this study, even though the prevalence of T2D and hypertension increased during follow-up time, the association remained statistically significant (data not shown). Another strength of the study was the standardized sampling of blood specimens in the morning after fasting according to EAU guidelines, avoiding diurnal changes in the levels of sex hormones (5, 6, 37, 38). Although a large part of the cohort could not participate in this study due to loss-to-follow-up, sensitivity analyses showed similar characteristics between participants and non-participants at the second visit. In a cross-sectional study on Finnish non-diabetic men (1896 participants), results suggested metabolic syndrome as a great contributor to the high CRP–low testosterone relationship (21). Moreover, our data indicate that CRP, a marker of inflammation, per se can predict the development of biochemical hypogonadism regardless of anthropometric measures such as WHR and BMI. The magnitude of the effect was observed to be lower when adjusting for BMI in all fully adjusted models although the same direction in the association was observed (data not shown). When assessing the relationship between hsCRP levels and biochemical hypogonadism, similar models were used (Table 3). Levels of TT remained almost constant until the age of 50, after which they declined somewhat more slowly compared to the decrease in cBT (Fig. 2A and B). Mean age at the first visit was 49.2 ± 11.6 and 58.9 ± 11.8 years at the second visit (Table 1). Testosterone was set as the dependent variable (TT and calculated bioavailable testosterone (cBT)) with logCRP as the independent variable. Characteristics of the study population were assessed using descriptive statistics to calculate means and confidence intervals. Calculation of bioavailable testosterone was done using the formula according to Vermuelen et al. (18). Blood pressure was measured in the supine position after 5 min of rest at baseline and follow-up. After exclusion, 625 men remained to be included in the final analyses. At the first visit, a random population sample of 1400 men was included, and 645 men fulfilled a similar protocol at a 10-year follow-up visit. This was a longitudinal observational study between 2002 and 2014 in Sweden. It is still unknown what role inflammation plays in the secretion of testosterone in men. Always consult a qualified healthcare provider with any questions about a medical condition or treatment. Low testosterone and high inflammation often coexist and worsen each other. Due to right-sided skewness, levels of hsCRP were log10-transformed at baseline (logCRP). We found that the new method gave 11% higher results compared to the method used at baseline, and this increase was similar for every age group. A total of 625 men were included in the final analyses (Fig. 1). The study population has previously been described, but in brief, a random population sample based on the census registry was selected between 2002 and 2005, and a follow-up visit was performed in the same population in 2012–2014 (9). Normal and optimal Testosterone/CRP Ratio ranges can vary by sex, age, and lab methodology. Low Testosterone/CRP Ratio levels below the standard range may indicate an underlying health condition that warrants further evaluation. Analyses were conducted on 1,559 men with complete data on CRP and sex hormone levels. Message and data rates may apply. You should consult your personal healthcare provider regarding any medical concerns or before making healthcare decisions.By providing your phone number, you agree to receive text messages from Function Health. The authors would like to express their gratitude to the participants from Vara and Skövde for making this study possible. Male hypogonadism is defined according to both biochemical findings and clinical symptoms, with highest predictive value shown by decreased morning erection, libido, and sexual desire (6). Furthermore, the incidence of T2D and hypertension increases with age as well as required treatment, further affecting the inflammatory-hypogonadic relationship. This could affect the precision and therefore increase the risk for type 2 error in the analyses. In this prospective study, we observed a strong association between high levels of high-sensitive CRP and low concentrations of bioavailable testosterone in men in both cross-sectional and longitudinal analyses, independent of other relevant cardiometabolic and lifestyle factors. In conclusion, our study confirms an independent association between high levels of hsCRP and low bioavailable testosterone concentrations 10 years later, independent of cardiometabolic and lifestyle factors as well as baseline concentrations. Similarly, a cross-sectional study by Tsilidis et al., including data from the NHANES population (809 participants), found that men with low testosterone were at higher risk of having high CRP independent of total body weight, age, medication, or other comorbidities (23). In the BACH study (1559 male participants), a significant association was found between CRP and both total and free testosterone levels independent of age, obesity, and comorbidities (25). To the best of our knowledge, no study has earlier presented data confirming a longitudinal association between inflammation at baseline and a decrease in both levels of cBT and TT, defined as biochemical hypogonadism. However, when participants with biochemical hypogonadism at baseline were excluded, a total of 38 men (6.4%) were found to develop low testosterone levels during the observation period. Of the 1,559 men included in the analysis, 87 (5.6%) had missing data on one or more covariates. As results for T and SHBG were similar when conducted on the larger group of men with these measures available compared to the subgroup of men with complete data on all hormones and CRP, results are presented for the subgroup of 1,559 men. A total of 12 men with missing or extreme values for T and SHBG were excluded from the analysis. Of the 2,301 men in BACH, blood samples were obtained for 1,899 (82.5%). As the distribution of CRP levels was skewed, log (base 10) transformations of CRP levels were used. Descriptive statistics, proportions for categorical variables and mean and standard deviations (SD) for continuous variables, were used to describe the analysis sample. In this assay, an antigen-antibody reaction occurs between CRP in the sample and an anti-CRP antibody that has been sensitized to latex particles, and agglutination results. This is a methodological challenge for all long-term observational studies investigating the changes in sex hormones. However, residual confounding cannot be excluded due to the observational nature of the study. This is a large cohort-based study of men, representative of the population in Sweden. This change in estimates was larger in the cross-sectional analyses than in the longitudinal ones (Table 3).