Confused by American Standard Unit for Free Test

Oops, I didnt see you had also posted the same link. Sorry about that. Have deleted my post since its a duplicate link.

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I feel bad for guys trying to make sense of their TT/fT numbers. Lots of moving parts and historical issues and artifacts.

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Very interesting, thanks for posting. I initially thought they were using wrong units before realizing it was pretty unlikely and then got lazy about looking into it more and decided to just go with ED as the consensus best method, but this makes a lot of sense

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At least a high confidence if not 100% :grinning:

Interesting, I’ve never placed too much value on it either way since I keep my TT high enough anyway.

You’d better be careful. If your levels go supraphysiological, the graph police will be coming for you!

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Haha thanks for the heads up

You mean Free T in general? I think Free T became the main thing I look at because my TT was very high when I got on TRT but Free T was completely tanked due to super high SHBG, so I learned early on not to care too much about TT.

Now that my SHBG has dropped considerably since starting TRT I would feel relatively comfortable going with TT if I had nothing else to look at

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Perhaps I missed the explanation, but I’m still trying to wrap my head around this FT stuff. Everyone including my doctors say it’s all about “Free T” and not so much “Total T.”

LabCorp (Direct) FT range is 6.8-21.5 pg/mL
Quest (Gold Standard / Dialysis) range is 34.0-155.0 pg/mL

A lot of the videos on the internet seem to say ~20 pg/mL is an ideal range. Some say 30-50’s. But then in this thread a lot of people are saying 30+ is dangerous. Nobody seems to say which range they are referring to.

But the two ranges above are very different, and 30-50 would be towards the bottom of the Quest range… so why is that dangerous?

Am I missing something? (Presumably yes)

And assuming those two ranges above; is there somewhere with some literature as to what would be considered low/dangerous on each? I’m ~10 pg/mL on LabCorp, and ~85 on Quest.

Really confusing.

Go back up to this post and read the links:

Pay attention to units and example for all the fT options.

Also this plot i did:

Even the “gold standard” equilibrium dialysis assays for fT havent been standardized across US reference laboratories yet. CDC is working on it. Examples above show that calculated fT by Veremulen method typically a decent estimate. Direct RIA free T method correlates with true fT but it is a factor typically 6-7 off once you keep track of units. Most people are not trained in units so are confused as hell and i dont blame them. It is very arcane. So numbers get thrown out without units and the shitshow continues.


Thanks. I’ve read it several times, as well as the thread on EM. As much as I want to say that I get it, I’m not sure exactly what the take away should be.

Different labs, different tests, different ranges. I get it.
Different FT calculation formulas, different results. I get it.

But my LabCorp and Quest both have the same units: pg/mL. Labcorp has me at ~10 which is pretty close to the bottom of their range. Quest has me at ~85 which is pretty close to the middle (which seems odd based on my lower TT value).

My understanding of the takeaway there is to ignore the value results, and just focus on the range derived from their samplings. So I’m towards the bottom, or towards the middle which doesn’t add much clarity.

Then I plug my results into a Veremulen calculator and it gives me a result of 9-10; but there is no range to give me context. So I’m not sure what the takeaway there is. Is that good, bad, dangerous, and how would I know because I can’t really use that number with LabCorp or Quest ranges?

Then you then see stuff like this on forums:

“Various Forums and YouTube TRT guys state many people don’t feel “optimized” until their Free T hits 25 and better yet, 30+.”

Is the unwritten assumption that everyone is referring to a Veremulen results caluclation (and not say Quest)?

I still hope I’m missing my “ah-ha” moment of clarity. But if every doctor had different blood pressure ranges using the same units it would be really frustrating to try and determine if you had low, high, or dangerous blood pressure. As just a normal dude trying to make sense of Free T… this is annoying complicated. :slight_smile:

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You have to pay attention to units and test type. Post the lab results and test descriptions and i will walk you through the aha moment. Then we can capture that for others to read.

Ok I went back and pieced this together:

As I shared above, Labcorp direct FT test is correlated but not absolute measure of fT. Quest dialysis fT test is.

Maybe a picture will help:

Note the slope of the line on the left panel of the figure. Note that slope (approx 0.15) is very different than the slope of the right panel (~1.2).

This confusion is from folks not being clear about units. The 20 and 30-50 numbers referenced are for an equilibrium dialysis FT measurement in ng/dl not pg/ml.

Note: 10 pg/ml = 1 ng/dl

Careful with units.

To convert Labcorp direct result multiply by 7 so

Labcorp result converted to absolute comparator = 7*10 = 70 pg/ml = 7 ng/dl

Quest ED FT = 85 pg/ml = 8.5 ng/dl

Vermeulen FT calculator gives 9-10 what? 9-10 ng/dl

As mentioned above, Vermeulen FT calculator may be 20% high compared to Labcorp FT by ED. 80%*10 ng/dl = 8 ng/dl which compares well with your Quest fT by ED result and transformed Labcorp direct FT result.

In summary:

Transformed Labcorp direct FT method: 7 ng/dl

Quest FT ED method: 8.5 ng/dl

Vermeulen calculated FT = 9-10 ng/dl

Transform of Vermeulen calculated free T to ED result = 0.8 * (9-10) = 7.2-8 ng/dl

So there we have it, a decent tight range of FT estimate using the data from multiple measurement assays and calculation option (7-8.5 ng/dl).

Until all the FT methods get harmonized why not just use the Vermeulen calculator for everyday work? Or pay for ED at Labcorp or Quest. Or know how to convert and work between the various options. :thinking:

As shown here, a reasonable physiologic range for FT is 5-28 ng/dl based on Labcorp FT ED method. What is confusing is Quest has a range of 3.5 to 15.5 ng/dl. So cross lab harmonization still needs to be done.

The takeaway is TOT channel gives the impression FT of 30-50 ng/dl is reasonable place to shoot for “symptom resolution” as per the experience of their members. 30-50 ng/dl is above physiologic range. 50 ng/dl is really high for a human (statistical improbably and reckless to be throwing out this range to people on the internet).

See this discussion (this thread and below) for more context about absolute fT measurements by ED above 30 ng/dl:

Please guys, I realize everyone is not a trained scientist but you have to keep track of units and assay type for this FT stuff to make any sense in any self-consistent fashion. Otherwise just look at your results with respect to reported reference range or just trust your provider given his/her/their experience. Of course you should do the later and make sure you have someone you can count on for your health care guidance. Not some weirdo on the internet.

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Do we know if all know:

1 deciliter (dl) = one tenth of a liter
1 milliliter (ml) = one thousandth of a liter
1 microliter (μl) = one millionth of a liter
1 nanoliter (nl)= one billionth of a liter
1 picoliter (pl) = one trillionth of a liter

The same applies to grams

Thank you for going through the numbers, I think it makes a bit more sense to me now.

Per my blood pressure analogy; this part still boggles my mind. If Free T is what is most important; the two largest testing labs having very different ranges for what gets interpreted as healthy values is just… confusing/concerning. Having some standards here would certainly help.

The first sentence of that one says a typical range of 9-25ng/dL Free T range. Just pointing this out because it’s somewhat humorous, as if that was the typical range my calculations from above would be below it. So many different ranges. :slight_smile:

This makes a lot more sense to me now, and is probably the most important part. I would roughly have to 3.5X my numbers to get to 30 ng/dL… and nearly 6X to get to 50. Values aside, either of those just sounds dangerous.

Having watched a lot of their videos; that definitely makes me re-question a lot of the advice/“knowledge” they are giving.

Thanks again. Hopefully some other normal dudes out there stumble upon this thread and it helps them as well.

My pleasure and hope it does clear some of this up for those interested.

Absolutely and perceptive observation. You are right, I wasn’t going to get into a pissing match with @disciplined_trt about 5-28 ng/dl vs 9-25 ng/dl. The context of our discussion was about going much higher above a reasonable physiologic reference range and not about the cutoff for the lower part of the range. I know it is shocking but even I have my limits for trying to not be an ass and for the most part I try to engage in constructive dialogue. :slight_smile:

In my opinion we have enough data to infer there is a risk to even imply this is a reasonable range to shoot for (again, they are throwing this info out to the whole distribution who may be listening and a significant fraction of those potential listeners have never had a fT of 30-50 ng/dl (at age 18 or 28 or whatever).

Hence, I made this thread to deal specifically with the greener grass theory of TT levels:

Take care and thanks for your thoughts and feedback.

And yes I completely agree here. Here is the same plot above except with linear range:


Yes I understand why good advice is to use each labs free T result only in context of the method’s reported reference range. But if you are selling an expensive assay that claims to be an absolute measure of free Testosterone then you would hope the US reference laboratories would have better agreement than this on the upper reference range.

This type of harmonization process was recently completed for TT by LC/MS-MS and I hope they get there with FT as well:

Until then, I use calculated FT via Vermeulen and have seen enough to think it is pretty close (close enough) to Labcorp FT by ED. Secretly many of us FT nerds believe Quest has some issues with their FT method (there are both direct and indirect FT methods via ED that I won’t bore people with). And I won’t even bring up the Tru-T algorithm which even makes things more confusing for high SHBG guys.

If you want to have some fun use both of these calculators and share your FT numbers from both.

Check out the labs who participated in CDC standardization program for TT:

Another example from a post today:

cfTV about 10% higher than Quest fT via LC/MS-MS with ED: