T Nation

Accuracy of Calculated Free Testosterone Formula in Men

Read an interesting study that reports calculed Free Testosterone is severely overestimated when calculated using SHBG and Albumin… when compared to measured free T via Equilibrium Dialysis. It is my understanding that the gold standard for Free T is to calculate it. Looking at my last blood work. My Total T is 382, SHBG 30, and Albumin 4.6… Based on calculations my free T should be 116 PG/Ml which is low-normal based on a reference range of 46-226pg/ml… However my actual measured Free Testosterone is 53 pg/ml. That is more than double what it should have been if I relied solely on calculating it and not by equilibrium dialysis measurement. Based on my experience thus far and the studies I have read, it seems Equilibrium Dialysis measurement is a better indicator of plasma levels and should be the gold standard. 53 pg/ml versus 116 pg/ml huge difference. Can anyone chime in for discussion?

Saying all FT calculators are severely overestimate is accurate, the Tru-T calculator is the only one you should be using, because all the other calculators are based off calculations before testing methods were finalized.

The direct FT measurement is not very accurate, TT is more accurate and is why doctors fixate on it. I usually see a big discrepancy between directly measured FT and FT percentage. What your labs cannot show is how sticky your SHBG is, it might bind androgens more strongly or loosely than the next guy.

The binding force of SHBG differs between individuals. Personally I think current laboratory testing is garbage and we have a long way to go towards improving our testing, it seems like everyone is using different reference ranges and there are no standards.

You can take the same blood sample and split it up into ten different samples and get ten different results, that’s pretty bad if you ask me.

I agree, but wouldn’t this be the reason why calculators such as Tru T are inaccurate? They rely soley on SHBG and albumin values… But if one’s SHBG is less or more sticky then two different individuals with identical SHBG, TT, and Albumin could in theory have the same “Calculated Free T” using Tru T but in reality have different actual Free T levels. Assuming one had a sticky SHBG and the other less sticky.

I think this would be the reason why measurements via Equilibrium Dialysis would give insight into how sticky someone’s SHBG is. Tru T says my free T is 116 pg/ml but my measured free is 53 pg/ml. Could this mean my SHBG of 30 is more sticky as my values are half of what Tru T says they should be.

I have noticed this as well… It seems like Quest uses pg/ml and Lab corp says it is pg/ml however given their reference range I would expect it to be NG/dl. Possible typo by lab corp?

Tru-T is in ng/dL, not pg/mL and you cannot compare or convert to other units as they aren’t interchangeable. You didn’t consider that when converting the units the reference ranges are different.

The Tru-T calculator is the best you’re going to get, Equilibrium Dialysis which isn’t really available to everyone.

I was with a different provider 3 years ago, used Labcorp then and now, the previous provider had FT in ng/dL, then when I use Discount Labs (Labcorp), now FT is in pg/mL.

You can’t do a 1:1 comparison.

You’re right I did convert the units… is it not accurate to just convert them from ng/dL —> pg/ml? Which one do you believe more. My quest direct free T or Tru T? Tru T has me much higher free testosterone really not that low… considering my SHBG is only 30 and TT is 382.

No you cannot because this just dilutes the results because the ranges are not the same.


1 Like

@systemlord Ok so is my pre-TRT free Testosterone actually low then? Tru-T says it is 11.63 ng/dl while Quest measured it at 53 pg/ml. Both seem low in my opinon. But who cares about my opinion lol.

Given my 382 ng/dl TT… my calcualted Free T of 11.63 is almost exactly 3% free T. Much higher than the common 1-2% optimal free T percentage. Thoughts?

Why wont they update this? Seems like they really are in a rush to fix it.

You can’t have optimal FT at the bottom of the reference ranges, you have to conclude the calculator you’re using is in error. Only the Tru-T calculator can be trusted, the other ones use incorrect calculations to arrive at the results.

My value of 11.63 ng/dl is using Tru-T. This is 3% Free T compared to my 382 TT. Is 11.63 nd/dl considered low? There are no standards for reference ranges…

No clue

I don’t have my albumin value, but I used 4.5. The calculated value from Tru-T for me is 46% higher than what I get from my blood results in November from Quest using Equilibrium Dialysis, converting to ng/dl. Top is FT, bottom is TT.

Blood work -

Tru-T -

Am I doing something wrong/missing something?

Which is correct?

This is what the study I read shows… I can link it here in a second. Equilibrium Dialysis in the study was found to be much more accurate when determining true Free Testosterone plasma levels. Also in the study it states that “calculated free T” is not reliable when compared to ED measurement.

1 Like

Based on 2159 serum samples and compared to over 5 different calculators… interesting.

“Commonly used cFT formulae significantly overestimate FT relative to laboratory measurement by ED in male serum samples. The accuracy of the formulae is not influenced by correction for serum albumin, obesity, ethnicity or gonadal status” This last part holds true for me and @bcostigan41… Our calculated free T using Tru-T is much higher than our acutal measured Free T… And based on this large study… The equilibrium dialysis measured Free T is much more accurate. For those who are relying on Tru-T… this study could prove that those who “think” they have optimal free T really could be on the lower side and need more Testosterone.

You cannot get an absolute answer in the TRT world, testing is in its infancy and almost random results with poor accuracy.

Calculated FT is all my provider uses, the Tru-T method. Be careful which study you believe because a lot of these studies are poorly done, studies are like people, they are unreliable at times.

Using the Tru-t number I provided above and my SHBG number of 26, what would you estimate my E2 to be?

You can’t estimate estrogen based off other values, you must test it directly. No one can answer this question.

1 Like

This is true… however this study was done over a matter of years and includes a fairly large sample size… the results did not show any correlation between ED measured and calculated and in fact pointed towards extreme over estimation when using a calculated Free T. This holds true for me as well. I wonder if we can gather our own lab numbers here and compare Tru-T versus ED measured… For all of those reading. Please post your calculated value and your ED measured value.

If one merely relied on Tru-T… it is possible their actual levels are still sub-optimal or a lot lower than they think. Could we be on to something here? Could this be why so many in “optimal levels” still struggle to find relief. Just a thought. I like to question things much like Socrates did lol.

1 Like