Variable characteristics with insulin assays

Factitious hypoglycaemia is a challenging diagnosis to confirm. Evaluation of surreptitious human insulin use can be distinguished from endogenous insulin excess by existing biochemical assays. However, the increasing use of insulin analogues poses a challenge because commercially available insulin assays detect these with varying accuracy and precision. Insulin analogues are increasingly used in diabetes management and the case outlined here highlights the variations in assay. Initially, the local assay (ELISA kit – Dako, Copenhagen) failed to detect a significant concentration of insulin (<6pmol/L; range 9.6–65.4pmol/L) which an external reference laboratory subsequently detected using the Mercodia Iso-insulin two-site immunoassay (Uppsala, Sweden). The key analytical point is the recognition that different immunoassays detect insulin analogues to varying degrees. Clinical teams need to consider this if such cases are to be recognised. Following recent media reports where surreptitious insulin administration may be implicated in inpatient mortality, this knowledge is crucial to empower us to accurately diagnose all cases of unexplained hypoglycaemia. Copyright © 2013 John Wiley & Sons. Practical Diabetes 2013; 30(3): 118–120