Free Testosterone units of measure

Driven Mad · Apr 17, 2018

Can anyone help me understand how free testosterone is measured and how the results are interpreted? In Dec of 2017 my free-t was tested by Quest. Results were 189 pg/mL with a range of (35 - 155). Recently went with Discounted Labs (Labcorp) and got back what they call "Direct" and the results were 13.2 pg/mL 6.6 - 18.1

How the heck am I supposed to compare apples to apples here if the ranges are so wildly different? I think I'm low but none of this makes sense.

All this makes me Driven Mad

Systemlord · Apr 17, 2018

The problem with directly measured free T is the fact that free T is release in multiple pulses throughout the day and the half life is very short lived, so 30 minutes later if could change. We rely on Total T together with SHBG to determine our free T using an SHBG calculator, 2-3% is considered normal, below that and you guess it, you're low.

Hopefully this simplifies things a little.

http://www.issam.ch/freetesto.htm

Driven Mad · Apr 17, 2018

Systemlord said:
The problem with directly measured free T is the fact that free T is release in multiple pulses throughout the day and the half life is very short lived, so 30 minutes later if could change. We rely on Total T together with SHBG to determine our free T using an SHBG calculator, 2-3% is considered normal, below that and you guess it, you're low.

Hopefully this simplifies things a little.

http://www.issam.ch/freetesto.htm

So the direct free T test is meaningless but this is the test that you get from Discounted Labs which, correct me if I'm wrong, is owned by the owner of this site? Also, the calculator requires albumin as an input. Why is this not included in the DL test matrix? I thought I was confused but this assures me that I am.

Driven Mad

Systemlord · Apr 17, 2018

If I had to guess it would be cost. Our SHBG holds onto most of our testosterone and release 2-3% as free T, this will get you more accurate free T numbers than anyother method.

It seems most who have problems with their testosterone have free T below 2% and if within the 2-3% have other issues (thyroid/cortisol) going on.

I never said free T was useless, a bigger picture is painted when you have bioavailable, free T (directly) and Total T and SHBG all in one shot. They can corroborate each other.

madman · Apr 18, 2018

Systemlord said:
The problem with directly measured free T is the fact that free T is release in multiple pulses throughout the day and the half life is very short lived, so 30 minutes later if could change. We rely on Total T together with SHBG to determine our free T using an SHBG calculator, 2-3% is considered normal, below that and you guess it, you're low.

Hopefully this simplifies things a little.

http://www.issam.ch/freetesto.htm

Equilibrium dialysis is the gold standard for measuring free t. http://www.eje-online.org/content/152/3/471.long

Calculated free t (provides an accurate estimate) and has been found to be as accurate as equilibrium dialysis.

Direct free t RIA method correlates well with free t by equilibrium dialysis but (does not provide an accurate estimate) of free t.

https://academic.oup.com/jcem/article/89/2/520/2840748

Driven Mad · Apr 18, 2018

Thanks guys,
I think I understand at least a little better. So using the calculator method I'm at
Free-T 10.1 ng/dL = 1.62 %
Bio- T 268 ng/dL = 43 %

Info I received in another thread indicates most would consider this on the low side. The effects of this on how I feel are quite pronounced.
Thanks again for the responses.

Driven Mad

Free Testosterone units of measure

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