Introduction: In making a diagnosis of androgen deficiency, reference ranges are key; they aid in dividing testosterone levels into low or normal. Therefore, the researchers established total testosterone (TT) and free testosterone (FT) reference ranges; they did this by using a community-based sample of men.
Methods: This study used the Framingham Heart Study (FHS) Generation 3; 456 healthy, non-obese men ages 19-40 were included. Using liquid chromatography tandem mass spectrometry, TT was measured. FT was calculated.
TT and FT results below the 2.5th percentile of the reference sample were considered low (TT < 348 ng/dL; FT < 70.0 pg/mL).
Three categories of conditions are associated with low testosterone levels: physical dysfunction, sexual symptoms, and diabetes. The association between these categories and low TT and FT was examined in the FHS broad sample (combination of Generations 2 and 3), the European Male Aging Study (EMAS), and the Osteoporotic Fractures in Men Study (MrOS).
Results: In the FHS Generation 3 reference sample, the following results were reported:
In the 3 cohorts, subjects who had low TT and FT were, when compared to those with normal levels, were more likely to have difficulty climbing stairs, a slow walking speed, or frailty and diabetes. Also in all 3 cohorts, men with low TT and FT were more likely to experience at least one of these: sexual symptoms (EMAS only), physical dysfunction, or diabetes.
Men in EMAS who had low TT and FT were more likely to experience sexual symptoms than men with normal levels.
Conclusion: This study created reference ranges from a healthy, young (age 19-40 years) community-based sample, and it gives a basis for identifying testosterone levels as normal or low. It was seen that, using these criteria, men with low TT or FT were more likely to experience sexual symptoms, physical dysfunction, and diabetes.
Commentary by Glenn R. Cunningham MD