Insulin: Know what your immunoassay detects. Evaluation of two new immunoassays.

BACKGROUND: Insulin is essential for glycemic regulation but diseases can cause a default or an excess of insulin secretion leading to dysregulated glycemia. Hence, measurement of insulinemia is useful to investigate hypoglycemia, determine the pathogenesis of diabetes and evaluate ß-cell function. Thus, diabetic patients need supplementation with recombinant human insulin and/or insulin analogues. Analogues have primary sequences different from native human insulin and may not be detected by some immunoassays. The objective of our study was to evaluate new insulin immunoassays by determining their ability to detect different types of human insulin or analogues. METHODS: This study compared the reactivity of two new insulin immunoassays with five well-established immunoassays on ten commercial insulins. We also measured insulin in blood samples from diabetic or pancreas transplant patients with known treatment. RESULTS: Contrary to recombinant human insulin, there were differences in the specificity to insulin analogues. We distinguished three immunoassay categories: those recognizing all types of insulin such as the non-specific BI-INS-IRMA®, Architect® and Access® immunoassays; those recognizing human insulin only (Cobas®); and those recognizing human insulin and analogues in variable proportions (Liaison XL®, iFlash® and Maglumi®). CONCLUSION: An accurate biological interpretation of insulinemia relies on knowledge of the specificity of the immunoassay used.

A novel fully-automated method to measure steroids in serum by liquid chromatography-tandem mass spectrometry.

Background: Steroids play a key role in numerous physiological processes. Steroid determination is a useful tool to explore various endocrine diseases. Because of its specificity, mass spectrometry is considered to be a reference method for the determination of steroids in serum compared to radioimmunoassay. This technology could progress towards more automation for the optimal organization of clinical laboratories and ultimately for the benefit of patients. Methods: A fully automated ultra-high-performance liquid chromatography-tandem mass spectrometry method was developed and fully validated to determine five steroids in serum. Sample preparation was based on protein precipitation with filtration followed by online solid phase extraction. Chromatographic separation was performed using a biphenyl stationary phase. Results: The method was successfully validated according to European Medicine Agency guidelines. Coefficients of variation did not exceed, respectively, 8.4% and 8.1% for intra- and inter-assay precision. Method comparison with radioimmunoassay showed a proportional bias for all compounds, except for testosterone in men. Comparison with another LC-MS/MS method demonstrated acceptable concordance for all steroids, although a small bias was observed for androstenedione. Conclusion: The novelty of this method is that it has been fully automated. Automation provides benefits in traceability and allows significant savings in cost and time.

[About a case of macro-FSH analytical interference]. / Une grosse FSH qui trompe énormément : à propos d'un cas de macro-FSH.

An 18-year-old woman was referred by her GP to the endocrinology department of the University Hospital of Bordeaux on suspicion of premature ovarian failure because of a disorder of the menstrual cycle and pathological results of biological exploration of the gonadotropic axis. Repeatedly-found elevated concentrations of FSH contrasted with a normal concentration of LH leading to a hypothesis of ovarian failure. However, different investigations favoured an analytical interference. The presence of heterophilic antibodies or anti-mouse antibodies (HAMA) was unlikely but, finally, a complex combining FSH and autoantibody (called macro-FSH) was evidenced.