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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Response from LabCorp About Their Incorrect Unit Usages For Their Free Testosterone - Direct - Test
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<blockquote data-quote="tareload" data-source="post: 194717"><p>Thanks for raising this issue and most people don't understand it very well. I don't blame them. However, the units used by Labcorp for the direct (RIA) free Testosterone assay are not incorrect. They are correct.</p><p></p><p>It's easy to think it's just a simple unit mislabel as I detail below in the attached posts. In reality the transfer function from direct (RIA) free T to calc-V Testosterone or Eq/LCMS Testosterone is typically closer to a factor of 5-7. All arcane but below you can find the details if you want the facts. Then this brings up the gory details of calculated free T vs measured EqD/LCMS free T (that's been beaten to death and not the topic at hand).</p><p></p><p>Nothing Valcour says above is wrong but it doesn't help explain the discrepancy. For the interested reader, I hope the following curated posts below help provide a useful resource to improve your understanding.</p><p></p><p><em>P.S. For the first appt I ever had on potential TRT I saw that the Dr. had ordered the direct free T assay and I spent the next 3 hours going through the details on why it was a problematic assay and not meaningfully physical when compared to human physiology as a % free T (as Dr. Cohen rightfully mentions in the original post above). Needless to say the Dr. laughed about it at the appt. As they say "ignorance is bliss" and understanding this stuff doesn't really lead to happiness. </em></p><p></p><p>Have a great day.</p><p></p><p>[URL unfurl="true"]https://www.excelmale.com/forum/threads/how-much-testosterone-is-converted-to-estradiol.8636/post-189044[/URL]</p><p></p><p>[URL unfurl="true"]https://www.excelmale.com/forum/threads/how-much-testosterone-is-converted-to-estradiol.8636/post-189054[/URL]</p><p></p><p>[URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3311[/URL]</p><p></p><p>From this post as summary of how the math works out in an "easy" to understand example:</p><p></p><p><em>In summary, a poor guy with high SHBG:</em></p><p><em>Total T = 1077 ng/dL</em></p><p><em>SHBG = 151 nmol/L</em></p><ul> <li data-xf-list-type="ul"><em>“Direct” RIA free T comes back = 0.72 ng/dL (<strong>0.067% of total T</strong>)</em></li> <li data-xf-list-type="ul"><em>Calculated free T by Vermuelen = 7.57 ng/dL (<strong>0.7% of free T</strong>)</em></li> <li data-xf-list-type="ul"><em>Calculated free T by Tru-T = 25.3 ng/dL (<strong>2.35% of free T</strong>)</em></li> <li data-xf-list-type="ul"><span style="font-size: 15px"><span style="font-family: 'Arial'"><em>Actual free T as measured by equilibrium dialysis probably 5-6 ng/dL (<strong>0.46-56% of free T</strong>)</em></span></span></li> </ul><p><em>So what’s the average guy to do if he really wants to understand his free T status? You can even argue about the validity of indirect vs direct equilbrium dialysis measurements and which one is correct if they don’t match. In short, it gets complicated.</em></p><p><em></em></p><p><em>EDIT: as I posted below, if you take the RIA result and multiply by 6.7:</em></p><p><em>0.72 ng/dL * 6.7 = 4.8 ng/dL which is very close to the range of 5-6 ng/dL I estimated would be shown via equilbrium dialysis. So if you want to convert your free T (via direct RIA) number to what it would be if your physician actually had ordered an appropriate test, then multiply by 7 not 10.</em></p><p></p><p>[URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3313[/URL]</p><p></p><p>[URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3314[/URL]</p></blockquote><p></p>
[QUOTE="tareload, post: 194717"] Thanks for raising this issue and most people don't understand it very well. I don't blame them. However, the units used by Labcorp for the direct (RIA) free Testosterone assay are not incorrect. They are correct. It's easy to think it's just a simple unit mislabel as I detail below in the attached posts. In reality the transfer function from direct (RIA) free T to calc-V Testosterone or Eq/LCMS Testosterone is typically closer to a factor of 5-7. All arcane but below you can find the details if you want the facts. Then this brings up the gory details of calculated free T vs measured EqD/LCMS free T (that's been beaten to death and not the topic at hand). Nothing Valcour says above is wrong but it doesn't help explain the discrepancy. For the interested reader, I hope the following curated posts below help provide a useful resource to improve your understanding. [I]P.S. For the first appt I ever had on potential TRT I saw that the Dr. had ordered the direct free T assay and I spent the next 3 hours going through the details on why it was a problematic assay and not meaningfully physical when compared to human physiology as a % free T (as Dr. Cohen rightfully mentions in the original post above). Needless to say the Dr. laughed about it at the appt. As they say "ignorance is bliss" and understanding this stuff doesn't really lead to happiness. [/I] Have a great day. [URL unfurl="true"]https://www.excelmale.com/forum/threads/how-much-testosterone-is-converted-to-estradiol.8636/post-189044[/URL] [URL unfurl="true"]https://www.excelmale.com/forum/threads/how-much-testosterone-is-converted-to-estradiol.8636/post-189054[/URL] [URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3311[/URL] From this post as summary of how the math works out in an "easy" to understand example: [I]In summary, a poor guy with high SHBG: Total T = 1077 ng/dL SHBG = 151 nmol/L[/I] [LIST] [*][I]“Direct” RIA free T comes back = 0.72 ng/dL ([B]0.067% of total T[/B])[/I] [*][I]Calculated free T by Vermuelen = 7.57 ng/dL ([B]0.7% of free T[/B])[/I] [*][I]Calculated free T by Tru-T = 25.3 ng/dL ([B]2.35% of free T[/B])[/I] [*][SIZE=15px][FONT=Arial][I]Actual free T as measured by equilibrium dialysis probably 5-6 ng/dL ([B]0.46-56% of free T[/B])[/I][/FONT][/SIZE] [/LIST] [I]So what’s the average guy to do if he really wants to understand his free T status? You can even argue about the validity of indirect vs direct equilbrium dialysis measurements and which one is correct if they don’t match. In short, it gets complicated. EDIT: as I posted below, if you take the RIA result and multiply by 6.7: 0.72 ng/dL * 6.7 = 4.8 ng/dL which is very close to the range of 5-6 ng/dL I estimated would be shown via equilbrium dialysis. So if you want to convert your free T (via direct RIA) number to what it would be if your physician actually had ordered an appropriate test, then multiply by 7 not 10.[/I] [URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3313[/URL] [URL unfurl="true"]https://forums.t-nation.com/t/realistic-trt-recomp-progress/253389/3314[/URL] [/QUOTE]
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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Response from LabCorp About Their Incorrect Unit Usages For Their Free Testosterone - Direct - Test
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