T Nation

Accuracy of Calculated Free Testosterone Formula in Men

Which would effectively be the same as saying… 160-310 pg/ml, correct? If one wanted to convert to pg/ml they could use Quests reference range of 46-226 pg/ml to compare it to. IE: My free T is 53 Pg/ml which is the same thing as 5.3 ng/dl. If i converted to ng/dl and wanted to compare ng/dl values I would have to compare it to a reference range that was based on nano grams per deciliter. Such as lab corp or Tru-Ts reference range

If the average person had to drink 1 gallon of water per day to be in a healthy range. wouldn’t that be the same as saying 128 fl oz… Units can be converted but reference ranges will have to be switched to match those units.

I could be way off here, but that is how we learn and grow by questioning and obtaining knowledge.

Not when it comes to laboratory testing, it’s too complicated for me to be able to explain. There’s a reason why doctors ignore FT measurements and fixate on the TT number.

The Endocrine Society position

Current methods for measuring free testosterone (fT) are technically challenging and not accurate. The widely used direct immunoassay and tracer analog techniques for measuring fT have been shown to be inaccurate. Equilibrium dialysis, the reference method against which other methods are compared, is labor-intensive and cumbersome, and therefore has had limited clinical adoption.

Recently, Endocrine Society’s Expert Panel acknowledged the experimental problems in fT measurements and concluded that “…the calculation of free testosterone is the most useful estimate of free testosterone in plasma…” For this reason they advocate for indirect “calculator” based methods, where free testosterone can be computed from the total testosterone, SHBG, and albumin concentrations.

Don’t you love how doctors are ignoring the number that matters the most? We really need to revolutionize modern medicine in respect to testosterone replacement therapy. Doctors who prescribe TRT should be more versed on the matter before subjecting their patients to something that they know little about… Seeing some protocols docs prescribe makes me wonder why they have a medical license.

The Tru T calculator gives a very high free T number for me too, for whatever that is worth. Something like 50% over measured. Which is right? I have no idea.

I read that part on Tru-T webiste. “Direct immunoassay and tracer analog techniques for measuring fT have been shown to be inaccurate”. Equilibrium dialysis on the other hand has limited research and is labor intensive… that is why I found the study interesting because Equilibrium Dialysis was researched to be more accurate when compared to 2000+ men and 5 calculators. ED could be the gold standard and due to it being expensive/labor intensive most would rather calculate.

So far me and one other have noticed the same as you. The study I linked says calculators widely over estimate when compared to Equlibrium dialysis… Im pushing for research here and correlation within our community. If free T is being over estimated many men might have lower Free T levels than they think…

Please post your results in my other thread

I only have free T direct measurements, not ED

I see… oh well. Im going to read through the forums to see what I can find on numbers.

If I plug in 2000 total T and 90 for SHBG I get 64 for free T on the truT site. Mine actually came back at 39 but it was the direct method, not ED

The total T test maxed at 1500 so I’m guessing at the 2000 number… it could be lower (I wouldn’t really expect it to be any higher)


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. Such inaccuracy relative to the reference method renders some cFT estimates unreliable for evaluating androgen deficiency as recommended by clinical best practice guidelines.

The last part “Relative to the reference method” is what I am referring to when I convert units and compared to the different reference methods.

This is a conclusive study… a large one that is finding calculators to be inaccurate. For those who rely soley on calculations… it might be beneficial to have levels measured. For those following along, if able please contribute in my separate thread and post your values. Any study can be wrong such as @systemlord stated. But that is why I am trying to start our own internal research here.

The cardiologist, the heart doctor are the most clueless about testosterone, without testosterone the heart is going to wither away and become weak and cardiologist are the least informed.

The problem is healthcare is dead and has been dead for some time now, but people are unaware that the healthcare we used to have has been replaced with sick care. Sick care waits for disease to strike, then offers treatment, it doesn’t prevent the disease because this is less profitable.

TRT is about treating and preventing disease, this is not how our sick care system operates.

Correct… look at how common anti-depressants are prescribed. I wonder how many could have benefited from TRT instead. Sad

For the sake of accruing a larger sample size. Can you post your values in the other thread even though they are direct immunoassay? Just make note of it when you post so others are aware.

I dont think you need to go through the hassle

calc FreeT according to Vermeulen shows a very good correlation to measured freeT. See Figure 2.

cFT - Z is a multistep, dynamic, allosteric model, its either the basis of Tru T or something very close.

Right, so two different studies with widely different results. Based on personal results and a few others here we have noticed a large gap between calculated and ED or direct measured. Collecting numbers from all of us within this forum will allow us to paint our own research picture. Its not a hassle when there is two different studies showing the exact opposite data. One thing is certain though mine and two others lab results are severely over estimated when comparing to Tru-T calculator.

Do not accept just one study, question everything and come to your own conclusions. Please read the study I posted above and contribute by posting your lab numbers (if you have them) in my other thread.

The study above is based on a sample of over 2000 serums and compares 5 different calculators to ED measured Free T… it was found that the calculators way overestimated levels. In my experience thus far and most of the labs I have seen… this is holding true.

@johann77 did you happen to read this part??

“Of the three methods we evaluated in this study, cFT-V, albeit systematically overestimating FT, most robustly approximated directly measured FT in samples representative of a broad range of T and SHBG levels“ This is directly from the study you just linked. They are saying that the cFT-V method is more accurate of the calculators… but it overestimates free T. Exactly what I am saying and what my study linked shows…

@systemlord please reference above posts. The basis of Tru-T is known to over estimate free T based on a study using the same algorithms Tru-T uses. This coupled with the study I linked and the results here at T-Nation suggest that calculated free-T is higher when compared to actual free T levels. I think the more we poke at this the more information we will discover.

“cFT-Z appears far off target relative to the results of direct ED in this study as well as compared with a substantial body of published data obtained with a variety of ED- or UF-based methods. Although cFT-L performs well in the midrange levels of serum T and SHBG, the dependence of its accuracy on T and SHBG levels has clinical implications ( e.g. , underestimation by cFT-L of FT at low SHBG concentrations could impair the ability to detect hyperandrogenism“

Directly from the same published research. Multiple studies have it known that calculating free T leads to overestimation and slimmer chances of diagnosing hypogonadsim when relying solely on calculations. Men who have normal calculated Free T must push for measured free T, as symptom relief might not be felt until true measured levels are towards the higher end of the reference range.

The study you linked is from 2010 in which the CDCs hormone standardization program wasnt implemented. Long story short, T value measured using the CDCs T standard are about 25% lower now then they were in 2010. I tried to explain this in another thread. This brings the outcome of the 2010 and the 2018 study much closer together.

Link relative information on CDC’s hormone standardization program here. Very interesting to see. Even if the T values are 25% lower now… than in 2010. This would not effect correlation to free T levels then. We are comparing sample sizes from the same time frame in this case 2010. The study you posted is taking the guess work out of it and directly saying it overestimates when compared to direct immmunoassay or Equilibrium dialysis measurements. I think this is why most men need to be on the higher end of calculated Free T to feel good… Because in actuality their true measure Free T is a lot lower. I wonder how many are content with mid range calculated Free T levels but still feel like shit… If only they pushed for ED measured Free T… those in this case would really benefit from a dosage increase. Instead they probably spin in circles wondering why they have no symptom relief with “high free T levels”.

In any case… It serves us all well and benefits each of us to conduct our own research. Look at how far we have come in terms of protocol choices. Plenty of research would have you think every 2 weeks is an ok choice. We know from our trials and tribulations this is extremely false. We can standardize care among ourselves through our experiences. Think outside of the box and contribute to something greater. If you know others on TRT collect their information and post it to my thread. If we can collect significant data at some point… It might change the way we think of Free T levels and symptom relief.

This was on 100mg every 3 days or 50mg every 3 days? 460ish seems low for that dosage. Do you have the labs from then? I am on the same dosage and feel low T symptoms. I wonder if my levels are hanging around the 400s like yours did. If so a dosage increase may be in the future. Just have to wait and see what my labs say.