Authors Yeap BB, Alfonso H, Chubb SAP, Handelsman DJ, Hankey GJ, Norman PE, Flicker L.
Review Date July 2013
Citation J Clin Endocrinol Metab 2012;97(11):4030–4039
It is well recognised that testosterone (T) levels generally decline with age, particularly after 40 years of age. However, as symptoms of androgen deficiency can be nonspecific, the threshold for classifying low T in older men remains controversial. The relevance of assessing dihydrotestosterone (DHT) and estradiol (E2) is also unclear. Recommended methods for measuring T include early morning blood sampling and an accurate assay – currently mass spectrometry. The International Society of Andrology recommend that men with T <8 nmol/l may benefit from supplementation and the Endocrine Society recommend the lower limit of the normal range in healthy young men as the threshold – 9.8 to 10.4 nmol/l while others on an expert panel favoured a more stringent level of 6.9 nmol/l.
To assess the associations between T, DHT and E2 with outcomes of frailty and diabetes and cardiovascular disease (CVD) in older men (70 to 89 years old); and to establish reference ranges for this age group using liquid chromatography-tandem mass spectrometry (LC-MS).
As part of the second wave of the Health in Men Study (HIMS), over 4,000 community-dwelling Western Australian men aged 70-89 years (predominantly of Caucasian origin) completed a questionnaire and had a physical exam and venesection between 2001 and 2004. Plasma T, DHT, and E2 were assayed using LC-MS in early morning samples. Data linkage to hospital and cancer registries was used to ascertain chronic disease morbidity. Frailty was assessed with the FRAIL scale. “Healthy” older men were selected as those who self-reported excellent or very good health and had no history of smoking, diabetes, CVD, cancer, depression, or dementia.
After exclusion criteria were met, 3690 men were included in the analysis. Age ranged from 70 to 89 with 81% aged 70-79. Increasing age, higher body mass index and waist to hip ratio, dyslipidemia, diabetes, and higher LH were independently associated with lower levels of T and DHT. Increasing age, diabetes, and higher LH were associated with lower E2.
In a reference group of 394 men aged 76.1 +/- 3.2 yr defined as “healthy”, the 2.5th percentile for T was 6.4 nmol/l; DHT, 0.49 nmol/l; and E2, 28 pmol/l. Compared to the whole cohort, healthy men had higher T levels (mean 14.1 vs 13.1 nmol/l), higher DHT levels and similar E2 levels.
Applying these cut-offs to all 3690 men, 5.1% had low T; however, using the threshold of 12.1 nmol/l (from Framingham study, 2.5th percentile, men aged <40) 45% had low T. Men with low T (6/4nmol/l or lower) or low DHT had an increased odds ratio for frailty, diabetes, and cardiovascular disease. Men with both low T and DHT had a higher odds ratio for these outcomes. Low E2 was not associated with these outcomes.
The lower T threshold from this study of older men compared to those from healthy younger men reflect age-associated decline in T. The 2.5th percentile from this reference group of healthy older men may provide age-appropriate thresholds for defining low T, DHT, and E2 but further studies are needed to test their clinical utility in older men.
Points to Note
- The lower threshold of T for instigation of testosterone supplementation, apart from pathologically-based hypogonadism, remains controversial with various thresholds proposed.
- For older men without pathologically based symptoms, thresholds are not well defined with respect to symptoms such as low libido or low energy.
- This study provides thresholds based on the 2.5th percentile in a group of healthy older men that have potential clinical utility.
- The threshold of 6.4 nmol/l for T is in accordance with the more conservative ranges of a consensus panel – it is possible that men with higher levels of T might benefit from supplementation.
- Limitations of the study include: specific symptoms of androgen deficiency were not recorded; the men were predominantly Caucasian limiting generalisability of findings.
- There is no standardisation of LC-MS presently so caution is warranted for wide application of any reference ranges.