Total testosterone [T] is often used as a surrogate for T status. Free T would be more accurate. About 2% of T is 'free' - i.e. not bound to protein. Blood tests that report total & free T often estimate free T. About half of circulating T is bound to SHBG (sex hormone binding globulin) & is considered to be bio-unavailable. The rest is lightly-bound to albumin. The calculation uses measured SHBG but makes an assumption about albumin.
An interesting thing about SHBG is that numbers tend to go down as T rises, thereby increasing the freeT%.
As we get older, our total T tends to drop & estradiol [E2] tends to rise. When E2 is elevated, the body targets total T, since we make E2 from T. T production is inhibited and SHBG production goes up. i.e. less T is made & more T is bound to SHBG.
Albumin-bound T is considered to be weakly bound & therefore bioavailable, but free T is the immediately active form. Albumin is an inflammation marker and has been linked to survival. The LabCorp reference range is 3.6-4.8 g/dL, but one should aim for 4.5 or higher. Below 4.0, one should be seriously addressing inflammation, regardless of PSA, etc. For some reason, variation in albumin levels is not considered to be important when estimating free T.
"The study team that patients with free testosterone (FT) level in the lowest quartile (<4.42 nd/dL) had the highest proportion (15.6%) of very high risk (i.e. Gleason grade group 5) prostate cancer." i.e. GS = 4+5, 5+4 & 5+5 cases.
-Patrick
urotoday.com/conference-hig...
"Barcelona, Spain (UroToday.com) The relationship between testosterone and prostate cancer is controversial, with much remaining to be learned. While there is some contention regarding exacerbation of prostate cancer in men with higher testosterone, current systematic reviews show no such relationship.
Maxwell Towe, a clinical research fellow in the Department of Urology at UC Irvine Health, presented his findings on the relationship between total and free testosterone and its correlation with grade and stage of prostate cancer. His findings were further echoed by a German group presenting their data in the same session.
Overall, Towe’s study included 830 consecutive patients presenting to a single surgeon’s practice for management of local prostate cancer. Correlation between total and free testosterone were compared with clinicodemographic of age, preoperative PSA, prostate volume, pathologic grade, and pathologic stage. The study team that patients with free testosterone (FT) level in the lowest quartile (<4.42 nd/dL) had the highest proportion (15.6%) of very high risk (i.e. Gleason grade group 5) prostate cancer. Compared to those with high free testosterone, this was a statistically significant difference.
In multivariate analysis, lower free testosterone was an independent risk factor of very high-risk prostate cancer. This was found after controlling for previous indicators of prostate cancer aggressiveness: preoperative PSA, body mass index, and age. Even further, adding free testosterone into a nomogram for prostate cancer aggressiveness increased sensitivity and specificity significantly.
Overall, Towe stresses the importance of assessment of testosterone (and more importantly, of free testosterone) not only in prostate cancer patients but in older men in general. He cites previous work showing decreasing free testosterone with increased age. Future studies on testosterone replacement therapy and prostate cancer are encouraged, as these findings have significant and widespread benefit.
Presented by Maxwell Towe, Prostate Cancer and Men's Health Fellow, University of California, Irvine, Department of Urology, Orange, United States
Written by: Linda My Huynh, Senior Clinical Research Coordinator, Department of Urology, University of California-Irvine, at the 34th European Association of Urology (EAU 2019) #EAU19 conference in Barcelona, Spain, March 15-19, 2019."