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La Rivista Italiana della Medicina di Laboratorio 2020 Giugno;16(2):86-93

DOI: 10.23736/S1825-859X.20.00061-4


language: Italian

Insulin determination in serum: recent advances and further challenges

Anna VERO 1, Gabriella LAVALLE 2 , Andrea MOSCA 3, Roberto TESTA 4, per il Gruppo di Studio SIBioC-SIPMeL Diabete Mellito

1 Laboratorio di Analisi Chimico-Clinica, Azienda Ospedaliera Pugliese Ciaccio, Catanzaro, Italia; 2 Laboratorio Analisi, Ospedale di Bracciano, Roma, Italia; 3 Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italia; 4 Laboratorio Analisi Chimico-Cliniche e Molecolari, IRCCS-INRCA, Ancona, Italia

Insulin in the blood has the function of regulating carbohydrate metabolism by promoting the use of glucose in the tissues by changing the permeability of the cell membrane to glucose and promoting the synthesis of intracellular enzymes. Despite the important role, there are currently no indications on the measurement of basal insulinemia or during oral glucose loading to formulate the diagnosis of diabetes. Its dosage is recommended instead in the differential diagnosis of type 1 and type 2 diabetes in overweight children, in the diagnosis of hypoglycemia factitia and insulinoma. Its measurement also provides useful information on insulin resistance, β-cellular dysfunction, two fundamental aspects in the pathogenesis of diabetes mellitus and as a research tool in epidemiological studies. The numerous pre-analytical problems of insulin assay make the test difficult to use in clinical practice, preferring the dosage of C-peptide, which has the advantage of providing the same information as insulin but with less variability in distribution-degradation and with greater stay in blood. In the analytical field also, the main critical issues of the insulinemic assay concern the lack of standardization of the methods, the interference of any autoantibodies, the cross reactivity with the synthetic analogues used in therapy and the pre-analytical variables such as hemolysis and sample stability. Years after the discovery of the first diagnostic method, the problem of standardization remains open today. The results of several studies suggest that the origin of the discrepancies in the results among commercial methods is attributable to the lack of a standard reference method and the absence of a pure calibration material. For this reason, an IFCC international study group has been established in collaboration with the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) with the aim of developing a reference method for the insulin measurement using mass spectrometry techniques, to identify a high purity primary reference standard and to determine the analytical performance of commercially available insulin assays compared to the ID-LC/MS method. Among the pre-analytical interferents of insulin, hemolysis is certainly the most relevant and, as evidenced by studies on different analytical platforms, it depends on not only on the degree of hemolysis but also on the time and temperature of exposure to the hemolysis itself. Some authors have identified a correction equation, which, depending on the degree and time of exposure to hemolysis, provides insulin results such as those obtained from non-hemolysed samples. Regarding the stability of the sample, various scientific evidences, some in contrast to each other, indicate a greater stability of insulin on EDTA or lithium heparin plasma stored at 4 °C compared to the serum sample especially if there is a delay in the dosage. However, these aspects need further investigation.

KEY WORDS: Insulin; Reference standards; Serum; Diabetes mellitus; Diabetes insipidus

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