Public Service Announcement: "Piss Poor" Direct RIA fT measurement (HELP is on the way)

[tareload]

Hey Folks, thought I would update the graph for free T reference ranges based on LC-MS/MS+ED and compare with Labcorp's direct RIA fT reference range.

What the hell do you do with with your direct fT measurement if you want to compare with equibrium dialysis reference ranges? Take the Labcorp values in pg/ml and divide by 10 to get ng/dl. Then multiply by 6.67 to transform the direct fT measurement to the equilibrium dialysis scale.

Example and background / gory details here:

When does natural production return when stopping TRT?

Does natural production come back when stopping TRT? I’m 49 and have been on TRT for 3.5 years because I had severe depression and my Test levels were 150 tested 2 different times. I also had untreated sleep apnea at the time and was drinking a lot. I didn’t take any supplements at the time...

www.excelmale.com

Desperate advice needed quickly..too late?

First of all, I just want to thank all, for all the wealth of information that is shared here, more than anywhere else I have found on the internet. Excel Male, hands down the best! A special thanks to the moderators. Your knowledge on the subject of TRT, is better than any Dr. I have seen on...

www.excelmale.com

Enjoy!

Repeat. Long story short, take your direct RIA fT measurement in pg/ml, divide by 10 and multiply by 6.7 to get your value in ng/dl and on the same scale parity wise as the ED reference methods (at least as best as we can for now). Of course it doesn't help that the ED methods haven't been standardized and don't always agree with each other. Imagine that, the US reference laboratories don't all agree on the upper reference range for fT based on LC-MS/MS+ED. But we can't exactly blame that on the poor little direct fT assay, can we?

You also can bracket your direct fT "transform" value by your calculated fT with Vermeulen and Tru-T and compare the 3 to give you a decent range for thought and comparison with ED reference ranges below. Fun, isn't it?

Updated graphs:

You can see Labcorp's direct fT lower reference range snaps into place along side Quest/Mayo/Labcorp/ARUP ED methods. Of course there is still discrepancies on the upper reference ranges for the various reference labs. Tru-T (Zakharov 2015) still all by itself on the lower reference range (it must be lonely at the top of the bottom).

 

[Cataceous]

But then you have @madman posting this:

... Experiments using varying concentrations of SHBG and T showed that analog-based free T immunoassays reported free T results that were related primarily to total T and concluded that free T analog assays do not detect serum-free T [67]. Some argue that free T concentrations measured by immunoassays are as good as calculated free T but failed to note that the free T values obtained by immunoassays are only 1/7 of those measured by equilibrium dialysis indicating clearly what is measured by the analog free T assays is not free T [69]. The Endocrine Society Position Statement indicates that analog-based assays have poor accuracy, sensitivity, and poor correlation with the equilibrium dialysis method [18]. Free T by analog immunoassay correlates with total serum T and provides no additional information and is not a measure of free T and should not be used.​

Which echoes this earlier piece:

3.2 Analog immunoassay methods for free testosterone​

Analog immunoassay methods for free testosterone are no longer recommended by governing bodies [28]. These methods were developed as commercially available kits to combat the difficulty of performing free testosterone in most community laboratories by the reference methods described earlier. Briefly, these assays are based on a competitive principle whereby a radio-labeled testosterone analog competes with endogenous free testosterone in serum for a limited number of antitestosterone antibodies immobilized on a solid surface. This method assumes that the analog has little affinity for SHBG and albumin and hence, does not disrupt the equilibrium between bound and unbound testosterone in the patient sample. Analytical performance of these assays is generally quite poor; results generated tend to be an order of magnitude lower than equilibrium dialysis [61] or ultrafiltration [62,63]. In fact, free testosterone results generated from analog immunoassays correlate better with total testosterone, perhaps due to antibody binding of protein-bound testosterone [64] or fluctuations in concentration of SHBG [52]. For this reason, analog immunoassay measurement of free testosterone should not be performed as it is of limited clinical utility.​

For me Labcorp's direct IA test has a relatively poor correlation with dose (R-squared < 0.5) compared to fTZ and fTV (R-squared > 0.9).

 

[tareload]

Good points and this should be a good thread/review. My intent in first post was to get guys "conversant" in the language so to speak so they aren't paralyzed by their direct fT results. Once, they get the lay of the land let's get into the weeds regarding correlation, precision, accuracy between the free T methods and measurements for that matter.

Regarding ref 67 above:

https://academic.oup.com/clinchem/article/54/3/512/5628433

Clearly not all direct fT methods are created equal; but then again not all equilibrium dialysis methods for fT appear to be equal either.

Realistic TRT Recomp Progress

Haha, I’m sure there’s a whole lot more if you keep digging. As a side note… I’m the other weird one with SHBG comparable to BKB’s, I was at 151 just before starting TRT and, I believe, even higher than that a few months prior. I literally had “high” total T and a “low” free T on the same...

forums.t-nation.com

 

[tareload]

Mixture of endogenous production and exogenous T data points. Sorry I don't have more direct (analogue) data points. All Labcorp:

First plot: direct fT ("analogue") transform vs TT is quite linear. cFTZ also has about the same correlation coefficient (R2). cFTV much lower R2,

2nd plot is calculated %fT vs SHBG.

As shown previously, estimated %fT from cFTV much more sensitive to SHBG than cFTZ.

%fT estimated from direct fT transform much flatter vs SHBG (~2%).