@Andrewgen_Receptors
More posts from @cataceous over on my What is TRT… thread at EM regarding paper above. You’d do well to study this if you want to understand.
The issue with this study is that they are basing MCR on total T rather than free T. The standard equation used is:
Production_rate = MCR * Hormone_concentration
But as I argued above, the proportionality applies to free testosterone, not total. So the equation should be:
Production_rate = MCR * Hormone_concentration = MCR * FT = MCR * f(SHBG, T)
The reason it might appear to work anyway is because at constant SHBG, free T is nearly proportional to total T. So you get:
Production_rate = MCR * f(SHBG, T) ~= MCR * f1(SHBG) * T = MCRx * T
The problem is that their measured clearance rate, MCRx, is actually dependent on both the underlying metabolism (MCR) and SHBG. Unfortunately they don’t separate out the two, which potentially weakens their conclusions. The results are further muddied by the drop in SHBG—mainly in younger men—over the course of the experiment. It’s frustrating, because they did measure free testosterone, apparently by an accurate method, along with baseline and final SHBG values—so they did have the raw data needed to separate out the various effects.
So people know what we’re talking about I’ll insert my earlier criticism of the MCR definition in this same study. I think it shows where SHBG fits in, and I also think SHBG is pretty independent of true MCR. I’ve noted before that with SHBG varying from low 40s nMol/L to low 20s, my free testosterone appeared to stay linear with dose.
The issue with this study is that they are basing MCR on total T rather than free T. The standard equation used is:
Production_rate = MCR * Hormone_concentration
But as I argued above, the proportionality applies to free testosterone, not total. So the equation should be:
Production_rate = MCR * Hormone_concentration = MCR * FT = MCR * f(SHBG, T)
The reason it might appear to work anyway is because at constant SHBG, free T is nearly proportional to total T. So you get:
Production_rate = MCR * f(SHBG, T) ~= MCR * f1(SHBG) * T = MCRx * T
The problem is that their measured clearance rate, MCRx, is actually dependent on both the underlying metabolism (MCR) and SHBG.