T Nation

Free T or Percentage Free T, Which Is Better?

Have been looking over labs for testosterone at Labcorp and noticed lots of different T labs that can be drawn. Seems most providers look at Total T and Free T (direct)as a measure of T concentration in body.

Since most of T is bound looking at % of freeT vs Free T could be a more accurate in giving levels.

Question does anyone look at
Testosterone Free, Equilibrium ultrafiltration with Total Testosterone?

I think free-t is more useful, but only as a sign post to note when you start feeling good so you know where to stay. I think you could have a decent ratio but a shit free and still feel bad.

So total and free t are the usual tests. There’s a different one if you expect the total t to be rather high, like over 1500 I think.still total t but uncapped and a bit more expensive.

Am confused as to which is best too.

Some use

I did a lab corp test recently. Usually I do the eia not lcms. Lcms took a week to get the results. Next time I use the eia.

Here’s good reading on lab corp site

The concentration of free testosterone is very low, typically <2% of the total testosterone concentration. In most men and women, >50% of total circulating testosterone is bound to sex hormone-binding globulin, SHBG, and most of the rest is bound to albumin.1,2 Routinely available assay methods used to measure total testosterone are not sensitive enough to accurately quantitate the free testosterone fraction directly. Free testosterone is estimated in this test by a direct, analogue immunoassay method. This assay uses a labeled testosterone analogue that has a low binding affinity for both SHBG and albumin but is bound by antitestosterone antibody used in the assay. Since the analogue is unbound in the plasma, it competes with free testosterone for binding sites on an antitestosterone antibody that is immobilized on the surface of the microtiter plate well.

Several authors have found that the analogue method has good correlation with equilibrium dialysis,1-4 but have found that the analogue results were only about one-fourth as high. Another group found that the analogue method produced results directly comparable to equilibrium dialysis without multiplication by a factor.5 More recently, Winters and coworkers have found the analogue method to correlates better with total testosterone levels than with bioavailable testosterone determined by the ammonium sulfate precipitation method.6 They suggested that the analogue-free testosterone results might be misleading in men with low SHBG concentration.6 Ooi suggested that the problems observed by Winters6 might, in large part, be resolved by simply using a more appropriate population-based reference interval.7 Vermeulen and coworkers found that the analogue-free testosterone method correlated well with free testosterone by equilibrium dialysis, but did not agree well with a free testosterone calculated from total testosterone and SHBG.3

https://www.labcorp.com/tests/144980/testosterone-free-direct

Agree. With so many options I wonder which is actually best. Do providers just send in the same lab without knowing the others or if what they order is best or maybe it does not really matter. Can you just take the free t divide by total t and that will give the the %freet T? Is so what does the % of free T mean in treatment dosing? Is it worth something or not