Reference intervals for free testosterone in adult men measured using a standardized equilibrium dialysis procedure

Low testosterone in primary infertile men is associated with a history of maternal obesity during pregnancy: Findings from a cross-sectional study

BACKGROUND

Maternal obesity increases offspring obesity risk, but limited data exist on its association with reproductive hormones in infertile males.

OBJECTIVES

To investigate the impact of maternal obesity during pregnancy on total testosterone levels in primary infertile men.

MATERIALS AND METHODS

Data from 418 men seeking medical help for primary infertility were analyzed. Demographics, clinical data, comorbidities, and history of maternal obesity during pregnancy were recorded. Testicular volume was assessed with Prader's orchidometer. Serum hormones, including calculated free testosterone, and semen parameters were collected. Low testosterone and low calculated free testosterone were defined as total testosterone <3 ng/mL and calculated free testosterone <120 pg/mL. Descriptive statistics and regression models evaluated associations between maternal obesity at pregnancy and both total testosterone and calculated free testosterone levels.

RESULTS

Median (interquartile range) age and body mass index were 36 (33‒40) years and 24.8 (23.1‒26.8) kg/m2. Men with low testosterone (n = 69) had higher body mass index, Charlson comorbidity index score, and follicle-stimulating hormone, but lower testicular volume, sex hormone-binding globulin, sperm concentration, motility, and normal morphology compared to men without low testosterone (all p < 0.04). Similarly, men with low calculated free testosterone (n = 226) showed higher sex hormone-binding globulin, lower estradiol, sperm concentration, and motility than those with normal calculated free testosterone values (all p < 0.02). Low testosterone (7.2% vs. 2.0%, p = 0.01) and low calculated free testosterone (4.4% vs. 1.0%, p = 0.03) were more frequently reported during maternal obesity. Multivariable logistic regression analysis showed that maternal obesity at pregnancy (odds ratio: 5.9), higher body mass index (odds ratio: 1.1), and lower testicular volume (odds ratio: 0.9) were independent predictors of low testosterone (all p < 0.01), adjusting for age. Multivariable linear regression analyses identified maternal obesity at pregnancy (β = ‒4.1) and lower testicular volume (β = 1.8) as independent predictors of calculated free testosterone (all p < 0.001), after accounting for age and body mass index.

CONCLUSIONS

Low testosterone is a frequent characteristic in primary infertile men. Although rare, maternal obesity at pregnancy is significantly associated with reduced total testosterone and calculated free testosterone levels. Further preventive strategies and close follow-up should be considered in this specific group.

Testosterone Therapy in Older Men: Present and Future Considerations

Testosterone is the classical male anabolic hormone, involved in sexual development, virilisation and regulation of body composition in adult men. Organic disease involving the hypothalamus, pituitary or testes may interfere with endogenous testosterone production. In such men, testosterone treatment effectively ameliorates symptoms and signs of androgen deficiency. However, non-gonadal factors including age, body mass index and medical comorbidities influence circulating testosterone, and older men have on average lower testosterone concentrations compared with younger men. In these men, testosterone treatment would be a pharmacological intervention requiring stringent justification via high-quality evidence from randomised controlled trials (RCTs). Recent RCTs show benefits of testosterone treatment to improve sexual function, anaemia and bone mineral density in older men, and to prevent or revert type 2 diabetes mellitus in men at high risk. Results from a large cardiovascular safety trial in men with or at risk of cardiovascular disease provide important reassurance as to cardiovascular and prostate safety of testosterone treatment. Key questions remain as to whether testosterone's anabolic and other effects can be used safely to counter reductions in lean mass associated with incretin-based weight loss medications in men with obesity, and whether it might prevent disabilities including frailty, osteoporotic fractures and dementia in older men generally. This last question could be answered by a new testosterone RCT, targeting men in the 65-80 years age bracket, which would necessarily be large and of extended duration. A composite endpoint could be used which integrates potential benefits and risks, such as disability-free survival.

Association between systemic immune inflammation index and serum testosterone and free testosterone in middle-aged and elderly men

BACKGROUND

Chronic inflammation is a pervasive feature of aging and may be associated with testosterone in middle-aged and older men. Systemic immune-inflammation index (SII) is a novel inflammatory biomarker. We aimed to assess the association between SII and serum testosterone and free testosterone (FT) in middle-aged and older men.

METHODS

Our study included males ≥ 40 years old in the 2011-2016 and 2021-2023 National Health and Nutrition Examination Survey. Multivariable regression analysis was used to explore the associations between SII and serum testosterone and FT in middle-aged and older men. Subgroup analysis was performed according to age.

RESULTS

About 5354 participants were included, of which 2450 contained FT data. Multivariable linear regression found that SII exhibited an inverse association with serum testosterone (β -0.05, 95% CI -0.07 to -0.03, P < 0.001) and FT (β -0.03, 95% CI -0.05 to -0.01, P = 0.032) in middle-aged and elderly men. After SII was grouped as quartiles, serum testosterone was significantly lower in SII quartile 4 than in SII quartile 1 (β -0.05, 95% CI -0.08 to -0.02, P < 0.001). However, FT was not significantly lower in SII quartile 4 than in SII quartile 1 (β -0.03, 95% CI -0.07 to 0.01, P = 0.135). In subgroup analysis, the serum testosterone results were consistent with the overall results. However, only in the ≥60 years group, SII exhibited an inverse association with FT (β -0.06, 95% CI -0.1 to -0.02, P = 0.002) and was significantly lower in SII quartile 4 than in SII quartile 1 (β -0.06, 95% CI -0.12 to -0.01, P = 0.049).

CONCLUSIONS

Our study revealed an inverse association between SII and serum testosterone and FT in middle-aged and elderly men, particularly among men ≥ 60 years.

Leveraging research into sex differences and steroid hormones to improve brain health

Sex differences, driven in part by steroid hormones, shape the structure and function of the brain throughout the lifespan and manifest across brain health and disease. The influence of steroid hormones on neuroplasticity, particularly in the adult hippocampus, differs between the sexes, which has important implications for disorders and diseases that compromise hippocampus integrity, such as depression and Alzheimer disease. This Review outlines the intricate relationship between steroid hormones and hippocampal neuroplasticity across the adult lifespan and explores how the unique physiology of male and female individuals can affect health and disease. Despite calls to include sex and gender in research, only 5% of neuroscience studies published in 2019 directly investigated the influence of sex. Drawing on insights from depression, Alzheimer disease and relevant hippocampal plasticity, this Review underscores the importance of considering sex and steroid hormones to achieve a comprehensive understanding of disease susceptibility and mechanisms. Such consideration will enable the discovery of personalized treatments, ultimately leading to improved health outcomes for all.

Efficacy and Safety of Testosterone Replacement in Testicular Cancer Survivors With Treatment-Influenced Hypogonadism: A Systematic Review

OBJECTIVE

The objective is to evaluate the efficacy and safety of testosterone supplementation in testicular cancer survivors with treatment-related hypogonadism.

DATA SOURCES

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards and used Embase, PubMed/MEDLINE, Cochrane Central, Web of Science Core Collection, Korean Journal Index, SciELO, and Global Index Medicus to obtain data in June of 2024.

STUDY SELECTION AND DATA EXTRACTION

Analyses evaluating testosterone supplementation in testicular cancer survivors with treatment-induced hypogonadism were included. Any analyses not assessing supplementation in this population or deemed unretrievable were excluded.

DATA SYNTHESIS

Ten analyses were included for analysis. A total of 332 bilateral or unilateral testicular cancer survivors with treatment-influenced hypogonadism were reviewed, with 238 patients receiving testosterone replacement. Eight of the 10 analyses assessed participants without poor quality-of-life (QOL) metrics, metabolic factors, and bone mineral density (BMD) at baseline and only found a significant benefit in fat distribution metrics with testosterone supplementation. Two analyses evaluated participants with poor QOL metrics or BMD at baseline and showed improvements in QOL or BMD with testosterone supplementation.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

There is robust evidence regarding the efficacy and safety of testosterone replacement in hypogonadal individuals but limited evidence specifically evaluating supplementation in testicular cancer survivors with treatment-influenced hypogonadism.

CONCLUSIONS

The results suggest testosterone replacement may be beneficial in patients with impaired QOL metrics, metabolic factors, and BMD at baseline; the results also suggest that routine supplementation for all individuals in this patient population lacks efficacy.

Effect of Bariatric Surgery on Male Infertility: An Updated Meta-Analysis and Literature Review

PURPOSE

We aimed to perform a meta-analysis to assess the evolution of sperm parameters and some sex hormones in obese males with idiopathic infertility who underwent bariatric surgery.

MATERIALS AND METHODS

We systematically searched MEDLINE and Embase databases for studies that documented sperm parameters and sex hormones before and after surgery.

RESULTS

Twelve studies have been included with a total of 285 patients. The heterogeneity was deemed moderate, with an I² value of 28%. The random effects model analysis indicated a statistically significant negative association between weight loss surgery and sperm concentration. The standardized mean difference (SMD) was -5.44, with a 95% confidence interval (CI) ranging from -7.65 to -3.22. The p-value was <0.0001. Twelve articles recorded the sperm volume before and after undergoing bariatric surgery. The analysis revealed no statistically significant alteration in sperm volume following surgery (SMD=-0.16, 95% CI -0.53-0.22; p=0.42). We assessed the total sperm count available in seven studies. The analysis did not prove any significant difference between groups (SMD=12.29, 95% CI -15.01-39.58; p=0.38). Evaluated in five studies, semen pH did not evolve significantly (SMD=-0.02, 95% CI -0.12-0.09; p=0.76). Also, total motility did not improve significantly (SMD=0.61, CI -2.86-4.09; p=0.73), and the included studies had a low heterogeneity (I²=29%). Following bariatric surgery, there was a significant increase in levels of both total testosterone and sex hormone-binding globulin (SHBG) (SMD=-6.40, 95% CI -9.12 to -3.67, p<0.00001 for total testosterone and -22.22, 95% CI -26.11 to -18.33, p<0.00001 for SHBG).

CONCLUSIONS

Our data suggests that bariatric surgery does not provide any benefits in terms of sperm parameters. Obesity likely affects fertility through processes that are not well understood.

Modulation of circulating free testosterone fraction by testosterone, dihydrotestosterone, and estradiol during testosterone replacement therapy

BACKGROUND

Testosterone, estradiol, and dihydrotestosterone share common ligand binding sites on sex hormone binding globulin and albumin. It is unknown whether and how changes in testosterone, dihydrotestosterone, and estradiol concentrations during testosterone replacement therapy affect free testosterone fraction.

OBJECTIVE

To determine the effect of changes in testosterone, dihydrotestosterone, and estradiol concentrations on free testosterone fraction during testosterone replacement therapy of men with hypogonadism.

METHODS

Using data from the Testosterone Trials, we assessed the association of changes in total testosterone, estradiol, and dihydrotestosterone concentrations over 12 months of testosterone replacement therapy with changes in free testosterone fraction, measured using equilibrium dialysis. We used random forests to evaluate the associations of predicted mean changes in free testosterone fraction with changes in circulating concentrations of each hormone at low, mean, or high change in the other two hormones.

RESULTS

Testosterone replacement therapy not only increased total testosterone, dihydrotestosterone, estradiol, and free testosterone concentrations, but also the percent free testosterone, even though sex hormone binding globulin levels did not change. The predicted changes in free testosterone fraction during testosterone replacement therapy exhibited a non-linear relationship with changes in each of total testosterone, dihydrotestosterone, and estradiol concentrations. Greater increases in testosterone, dihydrotestosterone, and estradiol levels during testosterone replacement therapy were each associated with higher model-predicted percent free testosterone. Substantially smaller changes in molar concentrations of estradiol and dihydrotestosterone had a greater effect on percent free testosterone than those in testosterone.

CONCLUSION

During testosterone replacement therapy of men with hypogonadism, changes in testosterone, dihydrotestosterone, and estradiol concentrations each altered percent free testosterone non-linearly. Small changes in estradiol concentrations exerted much larger effect on the free testosterone fraction than testosterone and dihydrotestosterone, suggesting complex interactions of the three hormones with the binding proteins. Assessment of changes in free testosterone during testosterone replacement therapy should include consideration of changes in all three hormones.

Use of calculated free testosterone in men: advantages and limitations

PURPOSE OF REVIEW

Due to technical requirements and high cost, equilibrium dialysis-free testosterone (T) measurements are not commonly available in clinical practice. Clinicians rely on calculated free T (cFT) as a proxy. This review discusses using free T as a second-line assessment, highlighting its relevance in preventing misdiagnosis and overtreatment of male hypogonadism.

RECENT FINDINGS

While there is consensus on measuring total T - comprising sex hormone-binding globulin (SHBG)-bound, albumin-bound, and free T - as a first step in diagnosing male hypogonadism, evidence confirms that aging and conditions like obesity influence both total T and SHBG levels. Furthermore, low free T has been associated with symptoms of androgen deficiency, even in men with normal total T. Clinicians should, however, be aware of limitations of free T calculations, particularly the lack of standardization. Recent developments include establishing age-stratified free T reference ranges measured by equilibrium dialysis.

SUMMARY

Free T remains a subject of longstanding controversy. Factors such as age and obesity can alter total T and SHBG levels. Free T serves as a second-line indicator of androgen exposure, taking SHBG fluctuations into account. Given that commonly used free T calculators only provide approximations of free T, there is a need to further standardize free T calculators.

Sociodemographic, lifestyle, and medical factors associated with calculated free testosterone concentrations in men: individual participant data meta-analyses

OBJECTIVE

Sociodemographic, lifestyle, and medical variables influence total testosterone (T) and sex hormone-binding globulin (SHBG) concentrations. The relationship between these factors and "free" T remains unclear. We examined 21 sociodemographic, lifestyle, and medical predictors influencing calculated free T (cFT) in community-dwelling men across ages.

DESIGN

This is a cross-sectional analysis in 20 631 participants in the Androgens in Men Study.

METHODS

Individual participant data (IPD) were provided by 9 cohorts. Total T was determined using mass spectrometry, SHBG using immunoassays, and cFT using the Vermeulen formula. Associations were analyzed using 2-stage random effects IPD meta-analyses.

RESULTS

Cohort median ages ranged from 40 to 76 years and median cFT concentrations from 174.3 to 422.8 pmol/L. In men aged 17-99 years, there was a linear inverse association of cFT with age (-57.2 pmol/L [95% confidence interval, -69.4, -44.9] per 1 SD increase in age). Calculated free T increased with increasing baseline body mass index (BMI) among men with BMI < 23.6 kg/m2, but decreased among men with BMI > 23.6 kg/m2 (-24.7 pmol/L [-29.1, -20.3] per 1 SD increase in the 25.4-29.6 kg/m2 BMI range). Calculated free T was lower in younger men, who were married or in a de facto relationship (-18.4 pmol/L [-27.6, -9.3]) and in men who formerly smoked (-5.7 pmol/L [-8.9, -2.6]), were in poor general health (-14.0 pmol/L [-20.1, -7.8]), and had diabetes (-19.6 pmol/L [-23.0, -16.3]), cardiovascular disease (-5.8 pmol/L [-8.3, -3.2]), or cancer (-19.2 pmol/L [-24.4, -14.1]).

CONCLUSIONS

Calculated free T was most prominently associated with age and BMI. The linear, inverse association with age, nonlinear association with BMI, and presence of diabetes, cancer, and sociodemographic factors should be considered when interpreting cFT values.

Testosterone is positively associated with coronary artery calcium in a low cardiovascular disease risk population

Background

In industrialized populations, low male testosterone is associated with higher rates of cardiovascular mortality. However, coronary risk factors like obesity impact both testosterone and cardiovascular outcomes. Here, we assess the role of endogenous testosterone on coronary artery calcium in an active subsistence population with relatively low testosterone levels, low cardiovascular risk and low coronary artery calcium scores.

Methodology

In this cross-sectional community-based study, 719 Tsimane forager-horticulturalists in the Bolivian Amazon aged 40+ years underwent computed tomography (49.8% male, mean age 57.6 years).

Results

Coronary artery calcium levels were low; 84.5% had no coronary artery calcium. Zero-inflated negative binomial models found testosterone was positively associated with coronary artery calcium for the full sample (Incidence Rate Ratio [IRR] = 1.477, 95% Confidence Interval [CI] 1.001-2.170, P = 0.031), and in a male-only subset (IRR = 1.532, 95% CI 0.993-2.360, P = 0.053). Testosterone was also positively associated with clinically relevant coronary atherosclerosis (calcium >100 Agatston units) in the full sample (Odds Ratio [OR] = 1.984, 95% CI 1.202-3.275, P = 0.007) and when limited to male-only sample (OR = 2.032, 95% CI 1.118-4.816, P = 0.024). Individuals with coronary artery calcium >100 had 20% higher levels of testosterone than those with calcium <100 (t = -3.201, P = 0.007).

Conclusions and Implications

Among Tsimane, testosterone is positively associated with coronary artery calcium despite generally low normal testosterone levels, minimal atherosclerosis and rare cardiovascular disease (CVD) events. Associations between low testosterone and CVD events in industrialized populations are likely confounded by obesity and other lifestyle factors.

Approach to the Patient: The Evaluation and Management of Men ≥50 Years With Low Serum Testosterone Concentration

Although testosterone replacement in men with classic hypogonadism due to an identified pathology of the hypothalamic-pituitary-testicular axis is uncontroversial, the role of testosterone treatment for men with age-related declines in circulating testosterone is unclear. This is due to the lack of large, long-term testosterone therapy trials assessing definitive clinical endpoints. However, men ≥50 years of age, particularly those who have a body mass index >25 kg/m2 and multiple comorbidities, commonly present with clinical features of androgen deficiency and low serum testosterone concentrations. Clinicians are faced with the question whether to initiate testosterone therapy, a difficult dilemma that entails a benefit-risk analysis with limited evidence from clinical trials. Using a case scenario, we present a practical approach to the clinical assessment and management of such men.