May 2026: Thirlwall Inquiry report delayed to at least September 2026 · six-baby inquests relisted to 2027 · CCRC review active · Shoo Lee Panel: no medical evidence of deliberate harm.
Medical explainer
C-peptide is produced when the pancreas makes its own insulin; injected (exogenous) insulin contains no C-peptide. A low insulin-to-C-peptide ratio is therefore presumptive of exogenous insulin — but only when the immunoassay used is forensically validated and confirmatory testing (mass spectrometry) is performed.
Two attempted-murder counts in the Letby case rested on insulin-to-C-peptide ratios from the Royal Liverpool laboratory. Named clinical biochemists have argued the immunoassay was not validated for forensic interpretation, that mass spectrometry was not performed, and that interfering antibodies and the immunoassay 'hook effect' were not excluded.
The Crown treated the laboratory ratio as forensic proof of exogenous insulin administration.
Prof. Adel Ismail, Prof. Geoff Chase and others have argued for the necessity of confirmatory mass spectrometry in forensic insulin determination. The Joint Insulin Report (May 2025) consolidated this view.
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