Context
Since the August 2023 Letby convictions, specialist peer-reviewed clinical- biochemistry and endocrinology journals have published on the forensic use of immunoassay insulin results. This page summarises the post-2023 literature record.
What the literature establishes
- Immunoassays are screening, not forensic. Every insulin immunoassay on the UK market, including the Roche Cobas, is designed to flag samples. Forensic distinction requires mass spectrometry.
- False-positive catalogue. Auto-antibodies, heterophilic antibodies, macro-insulin, assay interference, drug cross-reactivity — each produces false-positive results. The published literature catalogues each specifically.
- Sample-handling sensitivity. Gel tubes, delayed centrifugation, ambient-temperature storage each compromise forensic reliability. Combined, as in the Letby samples, they disqualify forensic use.
- C-peptide dissociation is non-specific. Adrenal suppression, sepsis, liver and kidney disease, drug exposure, repeated dextrose infusions all suppress C-peptide independent of exogenous insulin.
- Physiological-plausibility modelling. Prof. Geoff Chase’s work on insulin physiological modelling demonstrates the reported Letby values are implausible on the Crown’s own TPN-bag theory.
The Royal Liverpool protocol change
A specific documentary feature cited in the literature: the Royal Liverpool laboratory’s own 2012 protocol explicitly states the laboratory cannot diagnose exogenous insulin. The 2010 protocol in force at the time of Letby sample testing did not include that statement. The laboratory itself now acknowledges, in its post-2012 guidance, that results of the Letby type cannot diagnose exogenous insulin.
What the literature is not saying
No peer-reviewed post-2023 work defends the Crown’s framing against this literature. The specialty consensus is settled. Published defences of the Roche-Cobas-as-forensic-test position do not exist in peer-reviewed literature. This is the strongest form of Cannings-principle expert disagreement: not merely reputable experts disagreeing, but a settled specialty position against.
Read alongside
Our analysis of the peer-reviewed literature, Baby F insulin deep-dive, Joint Insulin Report summary, Dr Adel Ismail — biography, Dr Sarrita Adams — biography.