Practical advice for diagnosing hypogonadism
Guidelines provide a valuable guide for clinicians who lack experience in diagnosing and treating men with hypogonadism. However, guideline recommendations reflect “ideal” practices for “ideal” patients, which often differ from the medical scenarios encountered in everyday clinical practice. Furthermore, many guidelines do not clearly address essential aspects of hypogonadism, such as interpretation of testosterone levels, the problem with diagnostic thresholds and whether to place more importance on symptoms/signs or testosterone levels when making the diagnosis. Based on published data and decades of hands-on experience by expert clinicians, below is a summary of how to tackle these issues to ensure that men who may benefit from testosterone therapy don’t get neglected in daily clinical practice.
How to interpret testosterone levels when making the diagnosis of hypogonadism
It is well established that the prevalence of symptoms, signs and metabolic risk factors increases with decreasing testosterone levels.3,5 However, because of the large inter-individual variability in androgen receptor sensitivity, resulting in a corresponding inter-individual variability in testosterone levels at which the characteristic symptoms and signs of testosterone deficiency appear,6,7 it is impossible to set a universally applicable diagnostic threshold for what should be considered low testosterone. For instance, one man with a testosterone level of 400 ng/dL can suffer from bothersome symptoms, while another man with the same testosterone level is feeling well.8 Hence, an emphasis and reliance on testosterone levels alone hinders the clinician’s ability to diagnose and treat testosterone deficiency.9 For these reasons, the rigid application of testosterone thresholds to diagnose testosterone deficiency is illogical and contrary to good medical practice.10
Men with sexual symptoms of hypogonadism respond well to testosterone therapy across a wide range of pre-treatment total testosterone values, including low-normal total testosterone levels.20 These men may have low free testosterone levels that are not reflected in their total testosterone values.
The normal range for testosterone levels varies widely between assays and laboratories, and consequently the threshold for low total testosterone can vary 3.5 fold from 4.5 to 15.6 nmol/L (130 to 450 ng/ dL), while the threshold for high total testosterone can vary 3.3 fold from 16.8 to 40 nmol/L (486 to 1593 ng/dL).11 This means that the same blood sample can be categorized as low by one laboratory and within the normal range by another laboratory. Therefore, the same laboratory and assay should be used consistently, and results obtained from one laboratory cannot be compared to results from another laboratory. In clinical practice there are men who are highly symptomatic despite having testosterone levels above the recommended thresholds, and who have anecdotally experienced symptom/sign improvement with testosterone therapy.21 Clinicians are advised to use their clinical judgment in the management of such patients.4,21
Several guidelines recommend a trial of testosterone therapy in symptomatic men as a component of the diagnostic process, even if testosterone levels are above commonly suggested thresholds for low testosterone.13-15,18-22 In other words, regardless of pre-treatment testosterone levels, improvement in symptoms and/or signs of testosterone deficiency after the initiation of testosterone therapy can be regarded as a confirmation of a diagnosis of hypogonadism.23
What is the clinical value of assessing free testosterone levels?
This is an important aspect of testosterone physiology because free testosterone is considered to be the active fraction of total testosterone that is available to exert biological effects.29,30 Support for the clinical utility of assessing free testosterone comes from studies showing that free testosterone levels may correlate more closely to symptoms/signs of hypogonadism than total testosterone levels.31-34 It is notable that the age-related decline in sexual function may be due to age-related declines in levels of free testosterone rather than total testosterone levels.31,32,35,36 For instance, the European Male Aging Study found that men with normal total testosterone levels but low (calculated) free testosterone levels commonly had signs and symptoms associated with testosterone deficiency.31 Importantly, men with normal total testosterone/low free testosterone had similar impairment in overall sexual function score, reduction in sexual thoughts, erectile dysfunction and poor morning erections as men with low total testosterone/low free testosterone.31 After adjustment for age, smoking (nonsmoker vs. current smoker), alcohol consumption (<1 d/week vs. ≥1 d/week), depression (BDI score), BMI, and number of morbidities, only free testosterone was significantly associated with erectile dysfunction.32 This underscores the potential clinical utility of assessing free testosterone levels in the evaluation of androgen status, which in turn is dependent on knowing SHBG levels.
Considering that the prevalence of low free testosterone combined with normal total testosterone is nearly as high as the prevalence of both low total testosterone and low free testosterone, the European Male Aging Study recommended that assessment of free testosterone becomes part of the first-line diagnostic evaluation of hypogonadism, especially in older men. Clinical guidelines are increasingly recognising the utility of assessing free testosterone as part of the diagnostic workup of hypogonadism,12-14 and recommend that there should be no hesitation on the part of clinicians to offer testosterone therapy to symptomatic men with normal testosterone levels if they have low free testosterone levels.13
Proposed diagnostic thresholds for free testosterone by calculation or equilibrium dialysis range from 65 - 100 pg/ mL (225 – 347 pmol/L).12,13 The three most commonly used methods to determine free testosterone levels are38:
1. Equilibrium dialysis
2. Analog radioimmunoassay
3. By calculation
Equilibrium dialysis, the “gold standard” technique for measuring free testosterone levels, is expensive and not offered by every lab. Analog radioimmunoassay is the most widely used method for measuring free testosterone levels, however, it is less accurate and gives values for free testosterone that are considerably lower than those obtained by equilibrium dialysis. Numerical values provided by analog radioimmunoassay are approximately one eighth of those obtained by calculated free testosterone and equilibrium dialysis.39 A value <1.5 ng/dL by analog radioimmunoassay is approximately equal to calculated free testosterone of 100 pg/mL, and is suggestive of hypogonadism.40 Guidelines recommend using calculated free testosterone in clinical practice,12-14 based on its strong correlation with equilibrium dialysis.41,42
Online calculators make it easy to obtain calculated free testosterone levels, only requiring input of measured total testosterone and SHBG levels.
Free testosterone calculator
Measurement of testosterone levels – timing of the blood draw
In a large screening population of 3006 men ≥40 years, there was no change in mean testosterone levels from 6:00 am to 2:00 pm, and only a 13% decline from 2:00 pm to 6:00 pm.45 Furthermore, this study showed that there was no significant circadian variation in testosterone levels in men with type 2 diabetes or in men with testosterone levels in the hypogonadal range (<300 ng/dL).45 A more recent study confirmed the absent circadian variation in serum testosterone in young men with testosterone deficiency (mean age 33 years, BMI 32.6 kg/m2 .48 Given the data showing no significant change in testosterone levels until 2 pm and only a modest reduction thereafter,45 and absence of late afternoon decline in testosterone levels in both young and older men with low testosterone,45,48 testosterone levels obtained in the afternoon should not be considered invalid. Support for this position comes from the fact that there is no evidence showing that measurement of testosterone levels in the morning improves identification of men who may benefit from treatment. Furthermore, considering that there is no single universal threshold for defining “low testosterone”, and that symptoms/signs and clinical picture are of more importance in diagnosing hypogonadism than rigid reliance of testosterone levels – as explained in “How to diagnose hypogonadism”, imposing the burden on patients to do the blood draw in the morning is not warranted. More recently, the discussion of when to measure testosterone levels has centered on the acute impact of food intake on serum testosterone. A number of studies have shown that food ingestion can reduce serum testosterone compared with fasting.49-51 Clinical guidelines have not yet issued recommendations as to whether measurement of testosterone levels should require fasting samples.
Importance of symptoms/signs vs. testosterone levels when making the diagnosis of testosterone deficiency
Clinical guidelines require the presence of both symptoms and low testosterone levels to make the diagnosis of hypogonadism, but acknowledge the importance for physicians to use the clinical judgement. This may cause a dilemma for inexperienced physicians. A common misunderstanding is that the recommended diagnostic thresholds for what should be considered low testosterone are rigid rules. As explained above, this is not the case. A report of practices of expert clinician-researchers, who have decades of experience diagnosing and treating men with hypogonadism, underscored that symptoms are of key importance in making the diagnosis of hypogonadism, with blood tests used to confirm the diagnosis.4 Most expert clinician-researchers would offer a therapeutic trial of testosterone therapy to symptomatic men who have no contraindications.4 An International Expert Consensus report on fundamental concepts regarding testosterone deficiency and treatment likewise fully endorses the clinical importance of symptoms and signs for men with hypogonadism.52