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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Public Service Announcement: "Piss Poor" Direct RIA fT measurement (HELP is on the way)
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<blockquote data-quote="Cataceous" data-source="post: 223823" data-attributes="member: 38109"><p>But then you have [USER=13851]@madman[/USER] posting <a href="https://www.excelmale.com/forum/threads/what-to-measure-testosterone-or-free-testosterone.25287/#post-223782" target="_blank">this</a>:</p><p></p><p style="margin-left: 20px"><em>... 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]. <u>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</u> [69]. <u>The Endocrine Society Position Statement indicates that analog-based assays have poor accuracy, sensitivity, and <strong>poor correlation with the equilibrium dialysis method</strong></u> [18]. <u>Free T by analog immunoassay correlates with total serum T and provides no additional information and <strong>is not a measure of free T and should not be used</strong></u>.</em></p><p></p><p>Which echoes <a href="https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/immunoassay-method" target="_blank">this</a> earlier piece:</p><h3><p style="margin-left: 20px"><em>3.2 Analog immunoassay methods for free testosterone</em></p> </h3> <p style="margin-left: 20px"><em>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 <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/equilibrium-dialysis" target="_blank">equilibrium dialysis</a> [61] or <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/ultrafiltration" target="_blank">ultrafiltration</a> [62,63]. In fact, free testosterone results generated from analog <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/immunoassay" target="_blank">immunoassays</a> 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.</em></p><p></p><p>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).</p></blockquote><p></p>
[QUOTE="Cataceous, post: 223823, member: 38109"] But then you have [USER=13851]@madman[/USER] posting [URL='https://www.excelmale.com/forum/threads/what-to-measure-testosterone-or-free-testosterone.25287/#post-223782']this[/URL]: [INDENT][I]... 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]. [U]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[/U] [69]. [U]The Endocrine Society Position Statement indicates that analog-based assays have poor accuracy, sensitivity, and [B]poor correlation with the equilibrium dialysis method[/B][/U] [18]. [U]Free T by analog immunoassay correlates with total serum T and provides no additional information and [B]is not a measure of free T and should not be used[/B][/U].[/I][/INDENT] Which echoes [URL='https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/immunoassay-method']this[/URL] earlier piece: [HEADING=2][INDENT][I]3.2 Analog immunoassay methods for free testosterone[/I][/INDENT][/HEADING] [INDENT][I]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 [URL='https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/equilibrium-dialysis']equilibrium dialysis[/URL] [61] or [URL='https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/ultrafiltration']ultrafiltration[/URL] [62,63]. In fact, free testosterone results generated from analog [URL='https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/immunoassay']immunoassays[/URL] 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.[/I][/INDENT] 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). [/QUOTE]
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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Public Service Announcement: "Piss Poor" Direct RIA fT measurement (HELP is on the way)
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