Comparison of 11 Human Insulin Assays: Implications for Clinical Investigation and Research

Abstract

Background: The American Diabetes Association task force on standardization of insulin assays in 1996 showed wide variation in assay bias. Newer assays are specific for insulin, with several now available on automated immunoassay analyzers. Methods: In 2004, we compared 11 commercially available insulin assays by analyzing 150 serum samples (99 fasting/51 postprandial) from study participants with various degrees of glucose intolerance (exclusions being type 1 diabetes, insulin treatment, or presence of insulin antibodies). All assays were calibrated against International Reference Preparation 66/304. One assay was not specific for insulin and another was an RIA; 10 assays used enzyme/chemiluminescent labels. Bland-Altman difference plots were modified to use the mean insulin from all assays on the x-axis as a common comparator. Results: As in the 1996 study, insulin values from the different assays varied by a factor of 2, with the nonspecific assay ranking in the middle of the distribution. Spearman rank correlation coefficients, for ranking samples vs the mean, were 0.983-0.997. Both offsets and concentration-dependent differences were seen in the modified difference plots. Imprecision (mean CV) for automated assays (3%) was not significantly different from manual assays (5%). Similar values were obtained when one automated assay was run in laboratories in both the UK and the US. Results of 1 assay showed lower insulin concentrations in heparinized plasma than in serum.

Assessing the test–retest repeatability of insulin resistance measures: Homeostasis model assessment 2 and oral glucose insulin sensitivity

“…Insulin concentrations will vary depending on analytical method, including the use of plasma or serum. 25,26 Although some discrepancies may have resolved with improving technologies, they should be considered if older studies are referenced. Participant factors such as age, sex, body fat distribution and health status may also affect insulin sensitivity.…”

Interlaboratory Agreement of Insulin-like Growth Factor 1 Concentrations Measured by Mass Spectrometry

“…Part of the motivation behind the project was the known variability between immunoassays and even between the same immunoassay performed at multiple sites (23)(24)(25)(26)(27)(28), including for IGF-1 (3 ). Those reports were supported by the data available from the College of American Pathologists (CAP) proficiency testing program for IGF-1 (BGS survey), which from September 2011 to March 2013 demonstrated interlaboratory variability up to 33.5% CV.…”

Indicadores do perfil lipídico plasmático relacionados à resistência à insulina

“…Além do mais, foi utilizado um ensaio para insulina com ausência de reação cruzada com pró-insulina, o que garante maior confiabilidade das determinações plasmáticas. Apesar da praticidade na utilização do HOMA-IR na pesquisa, quando comparado ao clamp; na prática clínica, a determinação da insulinemia de jejum conta com as desvantagens da ausência de padronização entre os laboratórios, tanto no que diz respeito ao método quanto ao ensaio utilizado 24 . Em relação ao custo, são dosagens relativamente caras e indisponíveis em muitos serviços de saúde.…”