Analog-Based Free Testosterone Test Results Linked to Total Testosterone Concentrations, Not Free Testosterone Concentrations

Abstract

BACKGROUND:Analog-based free testosterone test results, sex hormone binding globulin (SHBG) concentrations, and total testosterone concentrations are somehow related. This study used new experiments to clarify these relationships. METHODS:An analog-based free testosterone immunoassay and a total testosterone immunoassay were applied to well-defined fractions of serum testosterone. First, they were applied to the 2 fractions (retentate and dialysate) of normal male serum obtained by equilibrium dialysis. Second, they were applied to covaried concentrations of SHBG and total testosterone. Third, they were applied to decreasing concentrations of SHBG and protein-bound testosterone, offset by increasing concentrations of protein-free testosterone, while total testosterone was held constant. RESULTS:The analog-based free testosterone assay and the total testosterone assay detected and reported serum testosterone test results from serum retentate, whereas neither assay detected the free testosterone in serum dialysate. Test results reported by the analog-based free testosterone assay followed varied concentrations of SHBG and total testosterone. When total testosterone was held constant, however, analog-based free testosterone test results did not follow varied concentrations of serum proteins or of free testosterone.CONCLUSION: An analog-based free testosterone immunoassay reported free testosterone test results that were related to total testosterone concentrations under varied experimental conditions. This alleged free testosterone assay did not detect serum free testosterone (the test results it reported were nonspecific) and should not be used for this purpose.

Free Testosterone Measurement by the Analog Displacement Direct Assay: Old Concerns and New Evidence

“…Although the latter approach is technically simple, care must be taken to assure the correct concentration of ammonium sulfate for complete precipitation of the SHBG-T complex. The fourth method is that studied by Fritz et al (1 ). Although this method is used widely, the analog-based assay described in their report is an automated black-box package with a proprietary radioactive buffer provided by the manufacturer; this class of assay has been criticized as having poor accuracy, sensitivity, and between-assay comparability and being influenced by the dilution of serum (2)(3)(4)(5)(6).…”

“…Fritz and coworkers (1 ) have provided data arguing against the validity of a popular analog-based direct assay for free testosterone (T). Their rigorous dissection of characteristics of the assay and use of carefully defined solutions demonstrates that the assay correlates generally with total T but does not measure dialyzable T; this observation is consistent with prior reservations about this class of assay by reported by the Endocrine Society (2,3 ) and of other investigators (4 -6 ).…”

The negative correlation between testosterone levels and age in healthy Indonesian men residing in the special capital province of Jakarta, Indonesia

“…LH levels in the circulation directly determine testosterone secretion by testes. 9 Only FT fraction that function in steroid action to target cells, including for bone and muscle growth. [10][11][12] Sex hormone binding globulin (SHBG) is a plasma glycoprotein synthesized by hepatocytes and also produced by the Sertoli cells.…”

Testosterone Replacement Therapy in Reversing “Andropause”: What Is the Proof-of-Principle?

“…[33][34][35][36] In these circumstances, a supplemental test assessing bioavailable or FT is helpful in clinical decision making. 36,37 However, different methods are available also for measuring TT and FT. 32,36,37 All of these methods are generally adequate for the diagnosis of male hypogonadism, but marked variations can occur from one laboratory to another. Moreover, different studies have indicated large variations and/or lacks of specificity in measurements of serum TT and FT by different methods commonly used in clinical chemistry laboratories (see Fig.…”

“…1). 12,[37][38][39] In recent years, there has been growing concern about the use of T replacement therapy (TRT) in middle-aged and older men who have borderline TT or even normal TT levels according to their ages. 40 Indeed, despite the lack of precise criteria for andropause, 26 both crosssectional and longitudinal studies have estimated that a substantial number of older men (i.e., especially aged ‡ 70 years) may have low sex steroid hormone levels.…”