Endocrine Abstracts

Objective

To establish a set of population derived reference ranges for plasma total testosterone, sex hormone binding globulin (SHBG) and calculated free testosterone (FT) values especially in older men.

Background

The age-related decline in testosterone concentrations in men is gradual and both cross-sectional and longitudinal data have shown that there was a small but significant decline in total and free testosterone concentrations from the fifth decade onwards. As most circulating testosterone (98%) is bound to SHBG and albumin, various mathematical equations have been used to calculate free testosterone levels.

Methods

We undertook a cross-sectional study of 184 predominantly older healthy men (age range 20–89, mean age 52 years) recruited from outpatient clinics with local ethical approval. Plasma testosterone concentrations were measured on the ADVIA Centaur (Bayer) and SHBG on the Immulite 2000 (DPC). FT values were calculated using the Sodergard, Vermeulen, Nanjee-Wheeler and Carter equations.

Results

Reference ranges (95^th centile) of plasma testosterone, SHBG and calculated free testosterone (FT) values were as follows :

There is a significant difference (P<0.05) between the measured plasma total testosterone and the various calculated FT values between the younger men (<40 years old) and older men (>40 years old) group.

Conclusion

This study provides a set of useful data for age-related reference ranges for total testosterone and calculated FT. The calculated FT is especially useful when the measured plasma testosterone is borderline low (between 7–12 nmol/l) in the investigations of older patients presenting with ‘andropause’ symptoms.