Research news

Older men are more likely to have primary hypogonadism while obese men, regardless of age, most often present with secondary hypogonadism.⁸ Thus, measuring both testosterone and LH can shed light on whether a man’s hypogonadism is caused by testicular or hypothalamic-pituitary dysfunction, and help guide therapeutic efforts. For example, because obesity and diabetes are strongly associated with secondary hypogonadism (low testosterone and low-normal LH)^9,10, monitoring testosterone together with LH can give an indication about the adequacy of treatment interventions targeted at reducing excess body fat and improving metabolic control.

However, over the past few years an additional form of hypogonadism has been identified - subclinical hypogonadism, also called compensated hypogonadism - which is characterized by normal testosterone levels in the presence of elevated LH levels.^8,11,12

In endocrinology, subclinical disorders are characterized by normal levels of a hormone, with altered levels, outside the reference range, of the hormone that stimulates or inhibits its production. A prime well recognized example is subclinical hypothyroidism, often characterized by normal thyroid hormone levels in the presence of elevated TSH levels.^13-15 Accumulating research shows that subclinical hypothyroidism, like the overt condition, is associated with a greater risk of heart disease, cardiovascular death and all-cause mortality.^16-18 This indicates that even though subclinical endocrine disorders represent milder forms of the clinically overt disease, they can have a significant negative impact on health outcomes.

Along those lines, it has been hypothesized that subclinical hypogonadism - normal testosterone levels in the presence of elevated LH levels – may be associated with neurological, psychological, and cardiovascular disturbances, including alterations of bone and glucose metabolism, as well as lipid profile abnormalities.⁵

However, while there are numerous studies on the health consequences of subclinical hypothyroidism and subclinical Cushing’s syndrome, subclinical hypogonadism has only recently begun to receive attention in medical research.

What this study adds

The study by Corona et al. sought to investigate the association of subclinical (compensated) hypogonadism with clinical and psychological characteristics of male subjects complaining of sexual dysfunction, studying in detail both subjective and objective sexual parameters. In addition, possible associations between subclinical hypogonadism and major cardiovascular event morbidity and mortality were examined.

By definition, total testosterone was significantly lower in men with overt hypogonadism (7.9 nmol/L) vs. men with subclinical hypogonadism (18.9 nmol/L) or men who were testosterone replete (17.6 nmol/L). LH levels were higher in subclinical hypogonadism (12.4 mU/L) vs. overt (3.4 mU/L) or testosterone replete (3.7 mU/L) men. When compared with testosterone replete (eugonadal) individuals, men with subclinical hypogonadism had higher SHBG levels, and therefore lower free testosterone levels (that is, less active testosterone).

While hypogonadism-related symptoms were more frequently present in overtly hypogonadal men than in subclinical hypogonadal men, men with subclinical hypogonadism still had significantly more hypogonadism-related symptoms compared with testosterone replete men. Furthermore, subjects with subclinical hypogonadism more often reported psychiatric symptoms, when compared with both testosterone replete and overtly hypogonadal subjects, even after adjusting for age and smoking and drinking habits. In contrast, no difference in psychiatric symptoms was observed between testosterone replete and overt hypogonadal men.

Compared with testosterone replete men, men with subclinical or overt hypogonadism had an increased predicted cardiovascular risk, even after adjustment for BMI and drinking habits. No difference was observed between subclinical and overt hypogonadism. Thus, this study found that men with subclinical hypogonadism have a similar cardiovascular risk as do men with overt hypogonadism.

In a follow up of 4.3 years of these men¹⁹ it was found that major cardiovascular event related mortality was significantly higher in men with either subclinical or overt hypogonadism compared with testosterone replete men, even after adjusting for age and concomitant morbidities.

Commentary

The main finding in this study is that subclinically hypogonadal men present with significantly more hypogonadal symptoms (primarily psychological) than testosterone replete men, and have an equally elevated cardiovascular risk as do men with overt hypogonadism. Perhaps the most striking finding is that major cardiovascular event related mortality was similarly elevated in men with subclinical hypogonadism as in men with overt hypogonadism, regardless of age and concomitant morbidities. Specifically, men with subclinical hypogonadism had an almost 10-fold increase in odds (risk) of cardiovascular mortality, comparable to that for overt hypogonadism. Thus, elevated LH in the context of apparently sufficient total testosterone levels may be an indicator of a general poor health status.

Support for this possibility comes from a previous prospective study showing that an elevated LH level may be a risk factor for heart disease.²⁰ In addition, subclinical hypogonadism has been significantly associated with physical symptoms²¹, and an inverse relationship exists between LH and muscle strength and frailty, independent of testosterone levels.²² The previously observed relation between LH and muscle strength and frailty, independent of testosterone, suggests that LH reflects serum androgen activity in a different way than do testosterone levels; it could possibly mirror the combined feedback effect of estrogen and androgen on the HPG axis.²²

Overall, these data indicate that the biological action of testosterone is indeed reduced in subclinical hypogonadism, even though total testosterone levels are the same as in testosterone replete men. This is supported by the elevated SHBG and lower free testosterone levels in subclinical hypogonadism, which was also previously reported in the EMAS (European Male Aging Study) study.²¹

Another explanation may be that although testosterone levels in men with subclinical hypogonadism remain above the thresholds for sexual symptoms, they may be insufficient to maintain “younger” levels of physical capacities.^23,24 Given the wide normal testosterone range^25,26, it is possible that testosterone levels in men with subclinical hypogonadism have declined from previously high normal to current low normal. High LH in this case may therefore be a biomarker for testosterone decline within the reference range, indicating a readjustment of the HPT feedback set point trying to compensate for deficiencies in testicular function, and/or defective testosterone feedback at the hypothalamic-pituitary level.²⁷

All this lends support for the view that measuring only total testosterone may give an incomplete clinical picture of men’s health status, and lead to missed opportunities for early intervention and prevention of further health deterioration.