Validity of radioimmunological methods for determining free testosterone in serum

Free testosterone: clinical utility and important analytical aspects of measurement

Testosterone, the most abundant androgen in men, is a steroid hormone that is synthesized predominantly by the testes. In women, minor amounts are synthesized in the ovaries. Androgen precursors are also produced and secreted from the adrenal glands in both sexes, where they undergo peripheral conversion to testosterone. Circulating concentrations are approximately 15-25 times higher in adult men compared to women. Maintenance of these levels is necessary for development and maintenance of secondary sexual characteristics, libido, growth, prevention of osteoporosis, and most importantly in men, spermatogenesis. Most testosterone circulates tightly bound to sex hormone-binding globulin (SHBG) or weakly bound to albumin. A minor amount circulates as free testosterone, and it is believed that this is the metabolically active fraction. Measurement of free testosterone is important in the diagnosis of many diseases, most importantly disorders of androgen deficiency in men (i.e., hypogonadism) and androgen excess in women (i.e., polycystic ovary syndrome and hirsutism). Many methodologies are available for free testosterone measurement including the reference methods (equilibrium dialysis and ultrafiltration), analog immunoassay, and calculated free testosterone based on measurement of total testosterone, SHBG, and albumin. Moreover, measurement of bioavailable testosterone, a combination of albumin-bound and free testosterone, also has clinical utility and can be measured by selective protein precipitation or calculation. In this review, the advantages and limitations of each of these methods will be discussed in the context of clinical utility and implementation into a routine hospital laboratory. Furthermore, up and coming methodologies for free testosterone measurement, including liquid chromatography-tandem mass spectrometry, will also be discussed.

Free testosterone levels and implications on clinical outcomes in elderly men

BACKGROUND AND AIMS

Aging is accompanied by a progressive decline in serum testosterone. Evidence concerning the clinical manifestations of low serum testosterone levels is contradictory. We aimed to examine the age-related decline in testosterone and the possible clinical outcomes, including erectile dysfunction, prostatism, cognitive function, daily life activities, depression, and osteoporosis.

METHODS

One hundred and twenty men underwent comprehensive geriatric assessment. Testosterone and free testosterone levels were measured, geriatric assessment scales, International Index of Erectile Function (IIEF) and International Prostate Symptom Scale (IPSS) were performed, and bone mineral densities were determined.

RESULTS

The mean age of the 120 men was 73.8+/-5.90. A significant decrease in testosterone and free testosterone levels with increasing age was determined (p=0.021). It was also found that erectile dysfunction, as determined by IIEF (r=0.66, p<0.001), and symptoms of prostatism determined by IPSS (r=-0.23, p=0.016), were significantly associated with low free testosterone levels. Laboratory parameters, obesity, osteoporosis, cognitive function, daily life activities, and cardiovascular diseases were not significantly different between groups with low and normal free testosterone levels.

CONCLUSION

Age-related decrease in free testosterone may lead to erectile dysfunction and symptoms of prostatism in elderly men.

Using the Protein Chip to Screen Agonists and Antagonists of the Androgen Receptor

Based on its important physical and pathological function, the androgen receptor (AR) is regarded as a significant drug target. In this report, the authors describe a novel strategy of protein chip technology to screen agonists and antagonists of AR. First, the AR ligand binding domain (AR-LBD) was expressed in Escherichia coli, purified, and then immobilized on a silane-polysaccharide surface of a protein chip. Second, the affinities of methyltestosterone (MT) and fluorescent-labeled testosterone for the AR-LBD protein chip were determined. Third, a converse strategy of the protein chip was tested to evaluate its reliability as a drug screening method. Fourth, a 10,067-compound library was screened to find new ligands of AR. From the results, the Kdof testosterone and the IC50of MT are consistent with the literature (0.61 vs. 0.49 nM 2.88 vs. 3.90 nM, respectively). The Z′ factor of the high-throughput screening (HTS) method was 0.76, which meets the requirement of drug screening (>0.4). Finally, 3 active ligands of AR were identified with their IC50values of 3.63, 2.19, and 1.71 µM, respectively. In summary, the novel strategy of the AR-LBD protein chip was suitable for HTS at the molecular level. ( Journal of Biomolecular Screening 2008:276-284)

Androgen therapy for loss of desire in women: is the benefit worth the breast cancer risk?

OBJECTIVE

To contrast the limited evidence that androgen therapy is an effective treatment for low sexual desire in women with the extensive literature suggesting that androgens promote breast cancer.

DESIGN

Evidence from population studies of women is reviewed on the association between endogenous androgen levels and sexual function or satisfaction. Recent randomized trials of testosterone therapy for low desire are critiqued in terms of methodology and generalizability. Research on endogenous testosterone levels and breast cancer risk in both premenopausal and postmenopausal women is summarized, as are recent studies of androgenic hormonal therapy and breast cancer risk.

SETTING

Literature review.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Not applicable.

RESULT(S)

Endogenous androgen levels are not correlated with sexual desire in population-based studies of aging women. Factors that are strongly associated with low desire include pain with sexual activity, emotional distress, life stress, and relationship conflict. The efficacy of testosterone therapy for women's desire problems is modest. Expectancy effects were not adequately controlled in randomized trials. Epidemiological findings agree that higher endogenous serum androgen levels confer increased breast cancer risk both before and after menopause. Androgenic hormonal replacement regimens also increase the risk of breast cancer.

CONCLUSION(S)

Testosterone supplementation should not be prescribed to women with low sexual desire unless long-term studies can demonstrate its efficacy and safety. Treatments for low sexual desire in women should address its common correlates: relationship distress, emotional distress, and dyspareunia.

Time-Resolved Fluoroimmunoassay for 19-Nortestosterone Residues in Aquaculture Tissues

A competitive time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of 19-nortestosterone (17beta-NT) residues in aquaculture tissues. The limit of detection (LOD) was determined to be 0.08 ng g-1 and the limit of quantification (LOQ) was less than 0.8 ng g-1. The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of incurred aquaculture tissues and confirmed by liquid chromatography tandem mass spectrometry (LC/MS/MS). This proposed technique could be applied to routine residue analysis.

Androgen insufficiency in women

Androgens are directly secreted by the ovaries and adrenals in women, and androgen precursors from these glands are converted in a variety of peripheral tissues into androgens. The major androgen in women is testosterone, and its action in target tissues can be mediated through the androgen receptor or through the estrogen receptor after aromatization to estradiol. Low sexual desire that causes personal distress (or hypoactive sexual desire disorder [HSDD]) is the most common form of female sexual dysfunction, and androgen insufficiency is one cause of this problem. In addition to a low libido, the clinical construct of the female androgen insufficiency syndrome includes the presence of persistent, unexplained fatigue and a decreased sense of well-being. Although there is conflicting information about the relationship between serum testosterone concentrations and sexual desire, multiple randomized, double-blind, placebo-controlled treatment trials have demonstrated that testosterone improves libido significantly more than placebo. Doses that provide physiologic to slightly supraphysiologic serum free or bioavailable testosterone concentrations are safe and associated with only mild androgenic side effects of acne and hirsutism. Oral, but not parenteral or transdermal, testosterone may decrease high-density lipoprotein cholesterol. At present, no testosterone preparation has been approved by the FDA for the treatment of low sexual desire (HSDD), so all such therapy is considered to be off-label use at this time.

Measures of bioavailable serum sex hormone levels in aging Chinese by protein chip

The purpose of this study was to develop a protein chip technique based on receptor binding assays to measure bioavailable serum sex hormone levels (BSSHL). 224 aging healthy Chinese were investigated to get the referenced values of BSSHL for the first time. In the assays recombined sex hormone receptor proteins were jointed to polysaccharide coated slides to make protein chip, and the dose-dependence curves of sex hormone on chip were prepared. The data showed that this method had good precision (CV < 16%) and accuracy (Bias < 10%), and the sensitivity could reach 1 pmol/L. From the results, BSSHL of men and women declined with aging, but no significant differences were observed. The BSSHL of aging men were higher than those of women. The bioavailable serum androgen level of men was 52-112 pmol/L, women's was 3-70 pmol/L and the whole group was 41.9-81.4 pmol/L. The bioavailable serum estrogen level of men was 0.8-3.0 pmol/L, women's was 1.2-2.5 pmol/L and the whole group was 0.6-2.64 pmol/L. Based on the assays, BSSHL measurement by protein chip can meet the needs of epidemiological studies in terms of speed, accuracy and sample volume required, and was helpful in quantitative assessment of aging people's health.

Validation of 5 routine assays for serum free testosterone with a candidate reference measurement procedure based on ultrafiltration and isotope dilution–gas chromatography–mass spectrometry

BACKGROUND/METHOD

The analytical validity of free testosterone (FTe) analog immunoassays is subject to much controversy. We revisited the validation of 4 analog assays and 1 FTe calculation procedure with a metrologically traceable reference measurement procedure (RMP) based on ultrafiltration and isotope dilution-mass spectrometry for direct measurement of Te in the ultrafiltrate. To this end, we performed split-sample measurements of 40 male sera.

RESULTS

Deming regression showed that 3 of the immunoassays had moderate to good correlation (0.8474 < or = r < or = 0.9241) with the RMP; however, the slope was markedly below 1. The FTe calculation procedure was in good agreement with this result. The Sy/x values for all assays were higher than the combined imprecision values, which indicate their susceptibility to matrix-related effects.

CONCLUSIONS

The study demonstrated substantial differences in analytical quality of FTe assays; however, the results suggested that after extending the validation with a larger variety of samples, recalibration of some analog assays might be worth further investigation.

Evaluation of a Candidate Reference Measurement Procedure for Serum Free Testosterone Based on Ultrafiltration and Isotope Dilution–Gas Chromatography–Mass Spectrometry

Background: To assess the analytical validity of free testosterone (FTe) measurements, a reference measurement procedure (RMP) is required. For steroids, isotope dilution–mass spectrometry is accepted as state-of-the-art technology. Because FTe is defined as the hormone fraction in serum water in equilibrium with the protein-bound fraction, the RMP should include a physical separation step. The use of equilibrium dialysis (ED) or ultrafiltration (UF) is advocated. Our objective was to develop such a candidate RMP.

Methods: We selected UF combined with isotope dilution–gas chromatography–mass spectrometry (ID-GC/MS) for direct measurement of Te in the ultrafiltrate. After optimization of the UF process, the complete procedure was validated by use of split-sample comparisons with indirect ED (iED) and symmetric dialysis (SyD).

Results: The candidate RMP gave maximum within-day, between-day, and total CVs of 3.0%, 3.1%, and 4.3%. The Deming regression equations for the respective method comparisons were: UF-ID-GC/MS = 0.98(iED) − 53 pmol/L (r = 0.94; Sy|x= 42 pmol/L) and UF-ID-GC/MS = 0.92(SyD) + 21 pmol/L (r = 0.97; Sy|x= 31 pmol/L).

Conclusions: We achieved the objective of a state-of-the-art candidate RMP, which agreed well with iED and SyD. However, we also demonstrated that a degree of discordance remains, which may require a decision from an authoritative organization on the recommended procedure to measure free hormone concentrations.

Interferences in hormone immunoassays

Despite the numerous potential interferences that were discussed in this article, immunoassays, in general, are robust measurement systems. There is no practical way to identify specimens a priori that are likely to have immunoassay interference. Therefore, laboratories must rely on communication from clinicians to identify suspicious test values that may be caused by assay interference. After laboratories are alerted, multiple investigations can be undertaken. The common causes of immunoassay interferences (see Box I) are dependent on the analytic format. Competitive assays are most likely to have problems with cross-reactivity, whereas immunometric assays most often have problems with heterophile antibodies. The simple steps to test for dilutional linearity, spiked recovery, heterophile antibody blocking,and testing with alternate technology can help in the evaluations of cases that are suspected to have assay interference.

Subgroup analysis of sex difference on the Vandenberg-Kuse mental rotation test

A large sex difference has been elicited on the Vandenberg-Kuse mental rotation test. Prior research emphasizes the biological root of this sex difference. In recent experiments we confirmed this viewpoint. A large sample was administered the test, and the distributions of scores for men and women (N = 138; 68 men and 70 women: ages 19 to 23 years). The mean scores were used as cut-off points to group the men and the women in different subgroups (Low/Women, High/Women, Low/Men, High/Men). There were large differences among all subgroups, reinforcing Kimura's testosterone hypothesis for sex differences in spatial ability.

Effect of four different oral contraceptives on various sex hormones and serum-binding globulins

In a double-blind, controlled, randomized, four-arm, bicentric clinical study, the effect of four oral contraceptives (OCs) on various hormone parameters and serum-binding globulins was investigated. Four groups with 25 volunteers each (18-35 years of age) were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinylestradiol (EE) + 2 mg dienogest (DNG) (30EE/DNG), 20 microg EE + 2 mg DNG (20EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG) or 20 microg EE + 100 microg levonorgestrel (LNG) (EE/LNG). The study was completed by 91 subjects. Blood samples were taken after at least 12 h of fasting on Day 21-26 of the preceding control cycle and on Day 18-21 of the first, third and sixth treatment cycle. The serum concentrations of free testosterone were significantly decreased by about 40-60% in all four groups, while those of dehydroepiandrosterone sulfate (DHEAS) showed a time-dependent decrease during treatment. Except for EE/EV/DNG, which increased prolactin significantly during the third and sixth cycles, no change was observed with the EE-containing preparations. There was a significant increase in the levels of serum-binding globulins during treatment, which differed according to the composition of the OCs used. The rise in sex hormone-binding globulin (SHBG) was highest during intake of 30EE/DNG (+320%) and lowest with EE/LNG (+80%), while the effect of 20EE/DNG and EE/EV/DNG was similar (+270%). The thyroxine-binding globulin (TBG) levels increased significantly, by 50-60%, during treatment with the DNG-containing formulations, while the effect of EE/LNG was less significant (+30%). The rise in corticosteroid-binding globulin (CBG), which occurred in all groups, was most pronounced in women treated with 30EE/DNG (+90%) and least with EE/EV/DNG (+55%), indicating a strong influence of EE and no effect of the progestogen component. In all treatment groups, the frequency of intracyclic bleeding rose in the first treatment cycle and decreased thereafter. Cycle control was significantly better with 30EE/DNG or EE/LNG than with 20EE/DNG or EE/EV/DNG. There was no significant change in blood pressure, body mass index or pulse rate throughout the study. In conclusion, the DNG-containing OCs caused a higher rise in SHBG and TBG levels than the LNG-containing preparation. The effects on CBG suggest a lesser hepatic effect of 2 mg EV as compared to 20 or 30 microg EE. In contrast to EE, the use of estradiol in OCs appeared to increase prolactin release, while the cycle control was better with the OC containing 30 microg EE.