Elsevier

Clinical Biochemistry

Volume 48, Issue 18, December 2015, Pages 1354-1357
Clinical Biochemistry

Short Communication
Commercial insulin immunoassays fail to detect commonly prescribed insulin analogues

https://doi.org/10.1016/j.clinbiochem.2015.07.017Get rights and content

Highlights

  • We assess the cross reactivity of 15 exogenous insulins in 10 clinical insulin assays.

  • Detection of insulin analogues was highly variable and ranged from 0% to > 140%.

  • Most assays failed to detect insulins with more than 1 amino acid difference.

  • Physicians need to be aware of the limitation of laboratory methods to detect exogenous insulin.

Abstract

Objectives

Blood insulin and C-peptide are key investigations in the differential diagnosis of hypoglycaemia. Analogues of insulin have modified primary-sequences compared to native human insulin, as such may not cross react with insulin assays. This has important implications in detecting surreptitious or malicious insulin administration.

The aim of this study is to assess the cross-reactivity of all insulins currently listed in the British National Formulary (BNF65, 2013) in clinical insulin assays currently used in UK clinical laboratories.

Design and methods

Sample sets were prepared for all 15 exogenous insulin classes listed in the BNF, at concentrations of 1000 pmol/L and 300 pmol/L, using pooled human serum. Samples were sent blinded to 5 participating analytical laboratories to cover analysis on the 10 major clinical insulin assays used in the UK.

Results

The ability of insulin assays to detect exogenous insulin preparations was highly variable and ranged from 0% to > 140% for a single exogenous insulin. Four assays were highly specific for the human insulin sequence and had no cross-reactivity with any synthetic analogue insulin. Two detected all insulin types (human sequence, animal and synthetic analogue), with the remaining having variable cross-reactivity.

Conclusion

The cross-reactivity of the 15 exogenous insulin preparations is highly variable in the assays used in clinical laboratories around the UK. It is important that laboratories and clinicians are aware of the limitations of their local assays to avoid missing the important diagnosis of hypoglycaemia secondary to excessive exogenous insulin. Where necessary, samples should be referred to specialist centres for insulin analysis and ideally by a validated and fully-quantitative mass spectrometry-based method.

Section snippets

Insulin analogues

Fifteen different insulin analogues were supplied by the Pharmacy at the Royal Devon and Exeter Hospital, UK. Details of the analogues assessed are provided in Table 1 and the amino acid sequences and structure modifications for each analogue are provided in the online methods.

Results

This cross-reactivity of commercial insulin assays to insulin analogues are shown in Table 1.

Discussion

We have shown that commercially available insulin assays fail to detect many insulin analogues commonly prescribed in the United Kingdom. This is the first study to comprehensively assess all combinations of available exogenous insulins and assays in the UK.

As the complexity of modification to the native human insulin molecule increases, the ability of assays to detect them decreased. Four of the insulins tested (Actrapid®, Humulin® S, Humulin® I and Insulatard®) have identical sequence and

Author contributions

CP, DC, AA, LC, CE, GW, and TM researched the data. CP and TM wrote the manuscript and researched the data.

DC, AA, LC, CE, and GW reviewed/edited the manuscript.

Acknowledgements

TM is funded by National Institute of Health Research CSO Fellowship, this paper's guarantor. DC is funded by the Diabetes Research & Wellness Foundation (RGAG/217). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. Technical support was provided by Nicholas Porter (Royal Surrey County Hospital), David Halsall (Addenbrooke's Hospital), Keith Burling (NIHR Cambridge Biomedical Research Centre, Core Biochemical Assay

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