European researchers have found that men with low free testosterone levels – but normal total testosterone levels – often have symptoms of hypogonadism.
The study was presented at the 17th European Congress of Endocrinology, held in Dublin, Ireland in May.
Men’s testosterone levels naturally decline as they get older. As this happens, their levels of sex-hormone-binding-globulin (SHBG) increases. The result is a larger decrease in free testosterone levels than total testosterone.
Still, some clinical guidelines recommend using total testosterone measurements to diagnose hypogonadism, with free testosterone assessed only when men are borderline.
With this in mind, the research team analyzed the testosterone levels of 3,369 men between the ages of 40 and 79 who were participants in the European Male Ageing Study.
Normal total testosterone was defined as ≥ 10.5 nmol/l and normal calculated free testosterone was ≥ 220 pmol/l. 2,540 men fell into this referent category.
The remaining men were classified into two groups. Group 1 (261 men) had normal total testosterone and low free testosterone. Group 2 (92 men) had low total testosterone and normal free testosterone.
After considering age, body mass index, and comorbidities, the men in Group 1 had more symptoms of hypogonadism than the men in Group 2. Such symptoms included fewer morning erections and higher rates of erectile dysfunction.
The researchers found no differences in sexual and physical symptoms when they compared the reference group (normal levels of both free and total testosterone) and Group 2 (low total testosterone and normal free testosterone).
“Not only total, but also [free testosterone] levels should therefore be assessed in men with hypogonadal symptoms,” the authors concluded.
According to Medscape Medical News, researcher Dr. Leen Antonio told conference attendees: “I think it would be preferable to use free testosterone rather than total testosterone to measure deficiency, especially in men who have borderline total testosterone levels.
“Our results suggest that free testosterone is more informative than total testosterone,” she added.
Antonio, Leen, et al.
“Low free testosterone is associated with hypogonadal symptoms in men with normal total testosterone levels: results from the European Male Ageing Study”
(Abstract presented at the 17th European Congress of Endocrinology in Dublin, Ireland. May 2015)
Medscape Medical News
“Free Testosterone May Help Diagnose Hypogonadism”
(May 19, 2015)