Determination of serum sex hormone binding globulin (SHBG) in preadolescent and adolescent boys

Evaluation of a new automated electrochemiluminescent sex hormone-binding globulin (SHBG) immunoassay

Serum sex hormone-binding globulin (SHBG) regulates the cellular bioavailability of SHBG-bound steroid hormones. Since variations in SHBG levels may affect the concentration of free, i.e., biologically active testosterone in serum, SHBG levels are commonly measured as a supplement to total testosterone determination. The recently developed electrochemiluminescence Elecsys SHBG immunoassay was evaluated analytically on a Modular E170 (Roche Diagnostics, Mannheim, Germany) immunoanalyzer. Major differences in SHBG concentrations have been described among the commercially available methods; we therefore compared the new method with an established SHBG immunoradiometric assay (IRMA) in 99 routine serum samples. To provide reference values to clinicians, SHBG concentration was measured by Elecsys in 304 serum samples from healthy volunteers and several relevant clinical subgroups. The within-run and total imprecision coefficients of variation were </=2.9% and </=3.3%, respectively. Functional sensitivity was at least 0.74 nmol/L. Recoveries after dilution of high-concentration samples in low-titer human serum or in assay diluent were within the range of 85-110%. The Elecsys SHBG assay correlated well (r=0.98) with the SHBG immunoradiometric assay, but values were higher for the Elecsys assay (Passing Bablok regression analysis: slope 1.14, intercept +2.5). In healthy subjects and clinical subgroups, we confirmed the differences in SHBG values reported in the literature. The Elecsys SHBG immunoassay provides precision and reliability in combination with reduced turnaround time.

Characterization of serum SHBG isoforms in prepubertal and pubertal girls

OBJECTIVE

SHBG is a circulating glycoprotein that binds dihydrotestosterone, testosterone and oestradiol with high affinity and low capacity. In girls, serum concentrations of SHBG gradually decrease with age due to a true fall in concentration and not to a change in the binding characteristics. The aim of our study was to determine the pattern of serum SHBG isoforms in normal girls in early childhood (ECh), late childhood (LCh) and puberty (P).

SUBJECTS

Fifteen normal girls were studied. They were divided into three groups according to their age: ECh: 3.7 +/- 0.9 years (mean +/- SD, n = 5); LCh: 6.4 +/- 0.5 years (n = 5); and P: 13.4 +/- 1.5 years (n = 5).

METHODS AND MEASUREMENTS

Preparative isoelectric focusing was used to isolate SHBG isoforms according to their isoelectric point (pI). Three groups of isoforms were isolated: SI: pI 5.2-5.4; SII: pI 5.4-5.6 and SIII: pI 5.6-5.8. Steroid levels in serum were determined by RIA.

RESULTS

The relative distribution of SHBG isoforms (% of the total SHBG recovered, mean +/- SD) in the three groups of girls studied was: ECh: SI: 25.8 +/- 9.9, SII: 53 +/- 10.5 and SIII: 21.2 +/- 1.6; LCh: SI: 8.8 +/- 3.1, SII: 58.8 +/- 12.2 and SIII: 31.8 +/- 8.6; P: SI: non-detectable; SII: 51.6 +/- 12.6 and SIII: 48.4 +/- 12.6.

CONCLUSION

These results indicate that serum SHBG is more heterogeneous before puberty. A considerable proportion of acidic isoforms are present early in life; they decrease during the prepubertal period and disappear when sexual development is completed. After puberty the glycoprotein is more homogeneous and an important proportion of more basic isoforms is present. At puberty serum SHBG not only falls in concentration but also has an altered sialic acid content which modulates its circulating half-life.

Hormone measures in finger-prick blood spot samples: new field methods for reproductive endocrinology

Comparative endocrine studies have notably advanced understanding of ecological factors that contribute to variation in human reproductive function. Such research has relied on methodological advances that permit hormone determinations in samples that are easily and safely collected, stored, and transported, most recently on measurement of steroids in saliva. This report seeks to further expand the scope of endocrine research by demonstrating the value of blood spot samples collected by finger prick. As a sampling strategy, finger-prick blood spot collection offers the advantages of short collection time, low invasiveness, repeatability, absence of postcollection processing, low biohazard risk, and ease of sample storage and transport. We document good sample stability and present sensitive assay methods for a range of steroids and proteins (FSH, LH, PRL, T, E2, DHEAS, androstenedione, cortisol, SHGB) in blood spots that require sample volumes of 3-12 microliters and display good reliability, specificity, precision, accuracy, and convertibility of results to plasma/serum equivalent concentrations. Laboratory evaluation was augmented by a feasibility study at a remote site in Papua New Guinea that confirmed validity and stability of blood spot collections under field conditions. Research applications of blood spot sampling are illustrated with a series of studies, including cross-sectional surveys for developmental and life span endocrinology, a longitudinal, population-based developmental epidemiologic study of puberty, and serial sampling in a dynamic study of neuroendocrine response to suckling. We conclude that the sampling features and wide range of measurable biomolecules of blood spots do constitute a methodological advance for endocrine research.

Changes in serum sex hormone-binding globulin and in serum non-sex hormone-binding globulin-bound testosterone during prepuberty in boys

Much evidence suggests that sex hormone-binding globulin (SHBG) influences the delivery of sex steroids to cells, probably by playing an important role in the distribution of serum sex hormones between SHBG-bound, albumin (HSA)-bound and free fractions. Recent evidence also suggests that HSA-bound testosterone (T), the major constituent of non-sex hormone-binding globulin-bound T, is biologically important. To examine the potential exposure of peripheral tissues to T during prepubertal years, the serum concentration of SHBG as well as the distribution of serum T in SHBG-bound, HSA-bound, free and non-SHBG-bound fractions was studied in 80 normal boys aged 0.5-14 yr, all at Tanner's stage G1 of sexual development. A gradual decrease in serum SHBG as a function of age was found without significant changes in the Ka of SHBG-dihydrotestosterone association. While regression analysis of serum total T vs age showed a 2.6-fold increase from 0.5 to 14 yr of age, those of non-SHBG-found, HSA-bound and free T vs age showed 8- to 9-fold increases during the same period. On the other hand, SHBG-bound T had only a 1.9-fold increase. Expressed as a function of serum total T, non-SHBG-bound T increased from 6.6 to 30.4%, the relative increment being greater for HSA-bound T than for free T. It is concluded that, with advancing age, there is a progressive increase in the T exposure of all tissues in normal prepubertal boys. It is speculated that, at the level of the central nervous system, this increase in serum bioavailable T could induce maturative changes in brain cells that result in the onset of puberty in normal boys.

Dynamics of SHBG response to testosterone. Implications upon the immediate biological effect of sex hormones

The dynamics of the changes in serum concentrations of SHBG to variations in serum testosterone was studied in rabbits. Castration of male rabbits failed to produce changes in SHBG within 2 days but induced a significant increment 2 months later. Administration of 15 mg of testosterone to 5 male castrates produced a rapid decrease in SHBG concentrations from 215 +/- 121 nmol/l before, to 114 +/- 15, 6 h after (mean +/- SD), while 25 mg of the androgen barely changed SHBG levels in 5 females (from 81 +/- 26 to 72 +/- 22). Three of the males and the 5 females showed a tendency to recover basal levels at 24 and 48 h. Since SHBG is a major regulator of the availability of sex hormones to be transported into tissue cells for both biological action and degradation, the rapid changes in serum SHBG induced by testosterone might play a role in controlling its own biological effect. A decrease in SHBG will result in a more effective stimulation in androgen-responsive tissues, but it will also favor a faster interruption of the effect by increasing the rate of degradation. These androgen induced changes in SHBG are apparently different in male and females.