The Relative Merits and Demerits of Various Methods of Measuring Free and Bioavailable Testosterone Levels
| Method . | Merits . | Problems . |
|---|---|---|
| Bioavailable Testosterone . | ||
| Ammonium sulfate precipitation of SHBG-bound testosterone | • Correlates well with free testosterone obtained by equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Conceptually measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Concanavalin A method | • More selective and less variable than ammonium sulfate precipitation to precipitate SHBG | • Technically difficult • Not easily automated • Not used currently by clinical laboratories • Measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Calculated bioavailable testosterone | • Based on law-of-mass-action theory or empirical equations • Simple to obtain | • Correlation between different algorithms is poor unless revalidated in a local laboratory • Dependent on correct estimation of the association constants for the binding of testosterone to SHBG (KT) and HSA (KHSA) • Results affected by the quality of total testosterone and SHBG and HSA measurements |
| Method . | Merits . | Problems . |
|---|---|---|
| Bioavailable Testosterone . | ||
| Ammonium sulfate precipitation of SHBG-bound testosterone | • Correlates well with free testosterone obtained by equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Conceptually measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Concanavalin A method | • More selective and less variable than ammonium sulfate precipitation to precipitate SHBG | • Technically difficult • Not easily automated • Not used currently by clinical laboratories • Measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Calculated bioavailable testosterone | • Based on law-of-mass-action theory or empirical equations • Simple to obtain | • Correlation between different algorithms is poor unless revalidated in a local laboratory • Dependent on correct estimation of the association constants for the binding of testosterone to SHBG (KT) and HSA (KHSA) • Results affected by the quality of total testosterone and SHBG and HSA measurements |
| Free Testosterone . | ||
|---|---|---|
| Equilibrium dialysis | • The reference method against which other methods are compared | • Technically difficult; operations in which the dialysis is performed vary across laboratories, contributing to high interlaboratory variability • Not easily automated • Few hospital clinical laboratories perform this assay • Expensive • Relies on accuracy and precision of total testosterone |
| Ultracentrifugation | • Comparable to equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Expensive • Relies on accuracy and precision of total testosterone |
| Free androgen index | • Represents the ratio of total testosterone/SHBG • Has been shown to correlate with free testosterone measurements • Simple to obtain | • Overly simplistic and inaccurate measure of free testosterone concentrations • Poor indicator of gonadal status • Dependent on accurate measurements of total testosterone and SHBG • Most experts do not favor its use |
| Analogue immunoassays | • Commercially available kits • High throughput and precision • Has been shown to correlate with free testosterone measurements | • Provides inaccurate estimates of free testosterone • Experts recommend against the use of direct analogue assays for measurement of free testosterone. |
| Salivary testosterone | • Simple to obtain | • May not be an accurate marker of circulating free testosterone concentrations • Affected by sample desiccation, contamination by food and blood |
| Calculated free testosterone | • Easy to use algorithms based on various models of testosterone binding to SHBG or empirical equations • Simple to obtain | • Dependent upon correct estimates of the association constants and stoichiometry for binding of testosterone to SHBG and HSA • Accuracy and precision affected by the accuracy and precision of the total testosterone and SHBG assays |
| Free Testosterone . | ||
|---|---|---|
| Equilibrium dialysis | • The reference method against which other methods are compared | • Technically difficult; operations in which the dialysis is performed vary across laboratories, contributing to high interlaboratory variability • Not easily automated • Few hospital clinical laboratories perform this assay • Expensive • Relies on accuracy and precision of total testosterone |
| Ultracentrifugation | • Comparable to equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Expensive • Relies on accuracy and precision of total testosterone |
| Free androgen index | • Represents the ratio of total testosterone/SHBG • Has been shown to correlate with free testosterone measurements • Simple to obtain | • Overly simplistic and inaccurate measure of free testosterone concentrations • Poor indicator of gonadal status • Dependent on accurate measurements of total testosterone and SHBG • Most experts do not favor its use |
| Analogue immunoassays | • Commercially available kits • High throughput and precision • Has been shown to correlate with free testosterone measurements | • Provides inaccurate estimates of free testosterone • Experts recommend against the use of direct analogue assays for measurement of free testosterone. |
| Salivary testosterone | • Simple to obtain | • May not be an accurate marker of circulating free testosterone concentrations • Affected by sample desiccation, contamination by food and blood |
| Calculated free testosterone | • Easy to use algorithms based on various models of testosterone binding to SHBG or empirical equations • Simple to obtain | • Dependent upon correct estimates of the association constants and stoichiometry for binding of testosterone to SHBG and HSA • Accuracy and precision affected by the accuracy and precision of the total testosterone and SHBG assays |
The Relative Merits and Demerits of Various Methods of Measuring Free and Bioavailable Testosterone Levels
| Method . | Merits . | Problems . |
|---|---|---|
| Bioavailable Testosterone . | ||
| Ammonium sulfate precipitation of SHBG-bound testosterone | • Correlates well with free testosterone obtained by equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Conceptually measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Concanavalin A method | • More selective and less variable than ammonium sulfate precipitation to precipitate SHBG | • Technically difficult • Not easily automated • Not used currently by clinical laboratories • Measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Calculated bioavailable testosterone | • Based on law-of-mass-action theory or empirical equations • Simple to obtain | • Correlation between different algorithms is poor unless revalidated in a local laboratory • Dependent on correct estimation of the association constants for the binding of testosterone to SHBG (KT) and HSA (KHSA) • Results affected by the quality of total testosterone and SHBG and HSA measurements |
| Method . | Merits . | Problems . |
|---|---|---|
| Bioavailable Testosterone . | ||
| Ammonium sulfate precipitation of SHBG-bound testosterone | • Correlates well with free testosterone obtained by equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Conceptually measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Concanavalin A method | • More selective and less variable than ammonium sulfate precipitation to precipitate SHBG | • Technically difficult • Not easily automated • Not used currently by clinical laboratories • Measures non−SHBG-bound testosterone, which approximates but does not equal HSA-bound plus unbound testosterone |
| Calculated bioavailable testosterone | • Based on law-of-mass-action theory or empirical equations • Simple to obtain | • Correlation between different algorithms is poor unless revalidated in a local laboratory • Dependent on correct estimation of the association constants for the binding of testosterone to SHBG (KT) and HSA (KHSA) • Results affected by the quality of total testosterone and SHBG and HSA measurements |
| Free Testosterone . | ||
|---|---|---|
| Equilibrium dialysis | • The reference method against which other methods are compared | • Technically difficult; operations in which the dialysis is performed vary across laboratories, contributing to high interlaboratory variability • Not easily automated • Few hospital clinical laboratories perform this assay • Expensive • Relies on accuracy and precision of total testosterone |
| Ultracentrifugation | • Comparable to equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Expensive • Relies on accuracy and precision of total testosterone |
| Free androgen index | • Represents the ratio of total testosterone/SHBG • Has been shown to correlate with free testosterone measurements • Simple to obtain | • Overly simplistic and inaccurate measure of free testosterone concentrations • Poor indicator of gonadal status • Dependent on accurate measurements of total testosterone and SHBG • Most experts do not favor its use |
| Analogue immunoassays | • Commercially available kits • High throughput and precision • Has been shown to correlate with free testosterone measurements | • Provides inaccurate estimates of free testosterone • Experts recommend against the use of direct analogue assays for measurement of free testosterone. |
| Salivary testosterone | • Simple to obtain | • May not be an accurate marker of circulating free testosterone concentrations • Affected by sample desiccation, contamination by food and blood |
| Calculated free testosterone | • Easy to use algorithms based on various models of testosterone binding to SHBG or empirical equations • Simple to obtain | • Dependent upon correct estimates of the association constants and stoichiometry for binding of testosterone to SHBG and HSA • Accuracy and precision affected by the accuracy and precision of the total testosterone and SHBG assays |
| Free Testosterone . | ||
|---|---|---|
| Equilibrium dialysis | • The reference method against which other methods are compared | • Technically difficult; operations in which the dialysis is performed vary across laboratories, contributing to high interlaboratory variability • Not easily automated • Few hospital clinical laboratories perform this assay • Expensive • Relies on accuracy and precision of total testosterone |
| Ultracentrifugation | • Comparable to equilibrium dialysis | • Technically difficult • Not easily automated • Few clinical laboratories measure it routinely • Expensive • Relies on accuracy and precision of total testosterone |
| Free androgen index | • Represents the ratio of total testosterone/SHBG • Has been shown to correlate with free testosterone measurements • Simple to obtain | • Overly simplistic and inaccurate measure of free testosterone concentrations • Poor indicator of gonadal status • Dependent on accurate measurements of total testosterone and SHBG • Most experts do not favor its use |
| Analogue immunoassays | • Commercially available kits • High throughput and precision • Has been shown to correlate with free testosterone measurements | • Provides inaccurate estimates of free testosterone • Experts recommend against the use of direct analogue assays for measurement of free testosterone. |
| Salivary testosterone | • Simple to obtain | • May not be an accurate marker of circulating free testosterone concentrations • Affected by sample desiccation, contamination by food and blood |
| Calculated free testosterone | • Easy to use algorithms based on various models of testosterone binding to SHBG or empirical equations • Simple to obtain | • Dependent upon correct estimates of the association constants and stoichiometry for binding of testosterone to SHBG and HSA • Accuracy and precision affected by the accuracy and precision of the total testosterone and SHBG assays |
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