Tom Fiers

Equilibrium dialysis followed by liquid chromatography–tandem mass spectrometry is considered the gold standard for the isolation and quantification of free hormones. However, this technique has not been described for the analysis of free 25-hydroxyvitamin D3. This study investigated analytical challenges, focusing on stability and adsorption of 25-hydroxyvitamin D3 in aqueous buffer environments, to be considered prior to method development of equilibrium dialysis for free vitamin D. Experiments revealed that 25-hydroxyvitamin D3 is highly prone to adsorption, and to a minor extent degradation, resulting in severe analyte loss already upon introduction of 25-hydroxyvitamin D3 into the aqueous environment, far exceeding observations in serum where protein binding provides significant protection. While chemical degradation only slightly contributes, strong surface adsorption accounts for the majority of 25-hydroxyvitamin D3 loss observed. In contrast, the addition of methanol to the buffer environment completely mitigated analyte loss, confirming the severe adsorption of 25-hydroxyvitamin D3 to recipient surfaces. However, incorporating methanol as a buffer component fundamentally altered experimental conditions, thereby potentially disrupting the physiological equilibrium between 25-hydroxyvitamin D3, vitamin D-binding protein, and albumin, and by extension the free fraction of vitamin D. Consequently, the large extent of, primarily, adsorption of 25-hydroxyvitamin D3 in aqueous environments represents an important consideration in setting up equilibrium dialysis experiments for free vitamin D. These findings additionally highlight a critical need for novel analytical strategies that prevent adsorption while maintaining physiological equilibrium in the assessment of free vitamin D.

Objectives: To compare clinical laboratory workflows for the assessment of androgens in men, focusing on total testosterone (T), sex hormone-binding globulin (SHBG) and free T, in clinical laboratories throughout Europe. Methods: An internet-based survey that included questions related to pre-analytical, analytical and post-analytical phases of androgen measurements was distributed between December 2022 and December 2023 by clinical laboratory/chemistry and endocrine societies. A total of 124 unique records from clinical laboratories in 27 European countries were analyzed. Results: Pre-analytical requirements for total T are subject to improvement as less than half of clinical laboratories recommended adequate morning sampling time and/or sampling in a fasting state. Total T was predominantly quantified using enzyme-linked immunoassay (IA) on automated platforms, with only one in four centers using mass spectrometry (MS), while SHBG was exclusively measured by IA. Additionally, free T was used by a majority of clinical laboratories, mainly reported as approximation by calculation of free T (cFT) using the Vermeulen formula. Generally, age-stratification was the preferred means of reporting reference ranges for total T, SHBG and cFT. However, considerate variability was observed in reported lower and upper limits, leading to the necessity of interpreting test results against assay-specific reference ranges, thereby hindering comparability of results between clinical laboratories. Conclusions: Our survey highlights significant inter-laboratory variability for the assessment of androgen status in men, implying non-commutability of clinical test results between different centers. In addition, we observed poor adherence to pre-analytical recommendations. These findings advocate for continued harmonization efforts of measurement procedures for SHBG and total/free T.

Sexual dimorphism influences cardiovascular outcomes in type 1 diabetes (T1D), with women facing a higher relative risk of macrovascular events compared to men, especially after menopause. This study hypothesizes that abnormalities in intermediate metabolism may be associated with cardiac autonomic neuropathy (CAN) in T1D. We aim to assess low molecular weight metabolites (LMWM) as markers of CAN in T1D, considering the effects of sexual dimorphism and age. In this cross-sectional study, we included 323 subjects with T1D (147 women and 176 men), with a mean age of 41 ± 13 years. A total of 44 women and 41 men were over 50 years old. CAN was assessed using Ewing’s tests, and serum metabolites were analyzed by proton nuclear magnetic resonance spectroscopy (¹H-NMR). Patients with CAN had lower levels of valine, isoleucine, and threonine, and higher levels of lactate, compared to those without CAN. These differences persisted after adjusting for BMI and estimated glucose disposal rate (eGDR). In a logistic regression model (R² = 0.178, p < 0.001), the main determinants of CAN included isoleucine [Exp(β) = 0.972 (95% CI 0.952; 0.003)], age [Exp(β) = 1.031 (95% CI 1.010; 1.053)], A_1c [Exp(β) = 1.361 (95% CI 1.058; 1.752)], and microangiopathy [Exp(β) = 2.560 (95% CI 1.372; 4.778)]. Sex influenced LMWM profiles, with over half of the metabolites differing between men and women. However, no interactions were found between CAN and sex, or between sex, age, and CAN, on metabolomics profiles. Our findings suggest an association between CAN and LMWM levels in T1D. The sexual dimorphism observed in amino acid metabolites was unaffected by the presence of CAN.

Context Genetic variation in SHBG structure may affect estimates of sex steroid exposure by altering the affinity of the protein for its ligand. Consequently, free hormone calculations assuming constant binding affinity may, for certain genetic variations, lead to incorrect diagnoses if genetic variation is not taken into consideration. Objective To investigate the effects of genetic variation in SHBG on calculated and measured serum free testosterone (T) in men. Design, setting and participants Population-based sibling-pair study in 999 healthy men aged 25 to 45 (mean, 34.5) years. Main outcome measures Genotyping using microarray (Illumina) for single-nucleotide polymorphism (SNPs) suggested to affect binding affinity and/or concentration of SHBG or T. SHBG concentrations were measured using immunoassay and in a subset (n = 32) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Total T was measured using LC-MS/MS. Free T was calculated and in a subset (n = 314) measured directly using LC-MS/MS after equilibrium dialysis. Results Allelic frequencies of analyzed SNPs ranged from 0.5% to 58.2%. Compared to wild-type, SHBG concentrations were lower in rs6258 heterozygotes (−24.7%; P < .05) and higher in rs6259 heterozygotes, rs727428 homozygotes, and carriers of rs1799941 (+10.8 to 23.1%; all P < .05). Total T was higher in rs727428 homozygotes and carriers of rs5934505, rs1799941and rs6259 (+3.9 to 21.4%; all P < .05). No clear effects on measured free T were found, except for a trend toward higher values in rs6259 homozygotes, significant for calculated free T (+18.7%; P < .05) in the larger global study population. Conclusion In these men, analyzed SNPs were relatively prevalent and affected serum concentrations of total T and SHBG but not calculated or measured free T except for a higher trend in rs6259 homozygotes.

According to the free hormone hypothesis, biological activity of a certain hormone is best reflected by free rather than total hormone concentrations. A crucial element in this theory is the presence of binding proteins, which function as gatekeepers for steroid action. For testosterone, tissue exposure is governed by a delicate equilibrium between free and total testosterone which is determined through interaction with the binding proteins sex hormone-binding globulin and albumin. Ageing, genetics and various pathological conditions influence this equilibrium, hereby possibly modulating hormonal exposure to the target tissues. Despite ongoing controversy on the subject, strong evidence from recent in vitro, in vivo and human experiments emphasizes the relevance of free testosterone. Currently, however, clinical possibilities for free hormone diagnostics are limited. Direct immunoassays are inaccurate, while gold standard liquid chromatography with tandem mass spectrometry (LC–MS/MS) coupled equilibrium dialysis is not available for clinical routine. Calculation models for free testosterone, despite intrinsic limitations, provide a suitable alternative, of which the Vermeulen calculator is currently the preferred method. Calculated free testosterone is indeed associated with bone health, frailty and other clinical endpoints. Moreover, the added value of free testosterone in the clinical diagnosis of male hypogonadism is clearly evident. In suspected hypogonadal men in whom borderline low total testosterone and/or altered sex hormone-binding globulin levels are detected, the determination of free testosterone avoids under- and overdiagnosis, facilitating adequate prescription of hormonal replacement therapy. As such, free testosterone should be integrated as a standard biochemical parameter, on top of total testosterone, in the diagnostic workflow of male hypogonadism.

Background Initiating feminizing gender-affirming hormone therapy (GAHT) in transgender women causes a steep decline in serum testosterone. It is unknown if testosterone concentrations change further and whether adrenal androgen levels change during feminizing GAHT and after gonadectomy. This limits clinical decision making in transgender women with symptoms attributed to GAHT or gonadectomy. Methods Transgender women (n = 275) initiating estradiol and cyproterone acetate (CPA) were included at baseline, and had follow-up visits after 3 months, 12 months, and 2 to 4 years. During follow-up, 49.5% of transgender women underwent a gonadectomy. Total testosterone (TT), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), and androstenedione (A4) were measured using liquid chromatography tandem mass spectrometry. Results After 3 months of GAHT, mean TT, calculated free testosterone (cFT), and A4 decreased by 18.4 nmol/L (95% CI, −19.4 to −17.4, P < 0.001 [ie, −97.1%]), 383 pmol/L (95% CI, −405 to −362, P < 0.001 [ie, −98.3%]), and 1.2 nmol/L (95% CI, −1.4 to −1.0, P < 0.001 [ie, −36.5%]), respectively, and remained stable thereafter. DHEA and DHEAS decreased by 7.4 nmol/L (95% CI, −9.7 to −5.1 [ie, −28.0%]) and 1.8 µmol/L (95% CI, −2.2 to −1.4 [ie, −20.1%]), respectively, after 1 year and did not change thereafter. After gonadectomy, CPA therapy is stopped, which induced no further change in TT, cFT, DHEA, DHEAS, and A4 compared with those who did not undergo gonadectomy. Conclusions Our findings confirm that after an initial drop, testosterone levels in transgender women remain stable. Adrenal androgens decrease in the first year of CPA and estrogen supplementation and remain unchanged after gonadectomy. Androgens did not change after gonadectomy and cessation of CPA. Correlates with clinical symptoms remain to be elucidated.

Health-care organizations are facing a high burden of ergonomic occupational accidents, and prevention is a continuous point of interest. In this manuscript, we describe the characteristics of ergo...

Objective: To provide insight in patterns and causes of aberrant thyroid function tests (TFT) and to propose a practical approach for clinicians. Methods: Starting from an illustrative case report, an extensive literature search was performed, resulting in a narrative literature review. Results: TFT that cannot be explained by the negative feedback principle of the hypothalamo-pituitary-thyroid axis are a challenge for every clinician. Various alternative explanations for these TFT should be considered before drawing the conclusion of thyroid disorder, since incorrect diagnosis and treatment can have severe consequences for the patient. For example, the combination of elevated or normal TSH with elevated free T4 or T3 levels may result from the use of certain drugs or lab interference, while low or normal TSH with low T3 or T4 can often be explained by non-thyroidal illness or central hypothyroidism due to pituitary failure. Correct identification of these clinical situations requires understanding thyroid hormone metabolism and action, knowledge of some laboratory techniques, and a multistep evaluation process. Conclusion: To avoid incorrect diagnosis and thus treatment, clinicians should be aware of the existence of aberrant TFT and know how to decipher them.