July 2026: Government declines to widen the Thirlwall terms of reference (16 July) · new 100-page insulin report to the CCRC challenging the trial evidence (9 July) · Thirlwall report still expected no earlier than September · inquests relisted to 2027 · Shoo Lee Panel: no medical evidence of deliberate harm.
Medical explainer
Insulin immunoassays measure insulin via antibody binding; mass spectrometry identifies insulin by mass-to-charge ratio. Immunoassays are quick and sensitive but susceptible to cross-reactivity, interference and the 'hook effect' at high concentrations. Forensic interpretation typically requires confirmatory mass spectrometry.
The Letby insulin counts rested on immunoassay results from the Royal Liverpool laboratory. No mass-spectrometry confirmation was performed. Independent clinical biochemists have argued this fails the forensic standard.
The insulin counts rested on immunoassay results from the Royal Liverpool laboratory, presented to the jury as measurements capable of distinguishing insulin the body made from insulin administered to it.
Independent clinical biochemists argue the method cannot bear that weight without confirmation. Immunoassays are susceptible to cross-reactivity, interfering antibodies and the 'hook effect' at high concentrations, where the assay's sigmoidal response curve becomes non-linear and readings unreliable. Mass spectrometry, which identifies insulin by mass-to-charge ratio, was not performed.
Because no confirmatory testing was done and no samples remain to test, the question of what the true values were cannot now be settled by re-analysis. The argument is about whether the method used could support the inference drawn from it, not about a competing measurement.
An immunoassay measures insulin via antibody binding — quick and sensitive, but indirect. Mass spectrometry identifies the molecule by its mass-to-charge ratio, which is why it is normally the confirmatory step for a forensic conclusion.
At very high concentrations an immunoassay's response curve stops being linear, so the number it reports can be distorted. In this context that matters because the reported values were treated as reliable measurements rather than as screening results needing cross-check.
Independent commentary states that Roche's own guidance for the Cobas assay requires confirmation by mass spectrometry before a result is treated as diagnostic of exogenous insulin.
No. It means the result was not confirmed to the standard normally required before it is used as forensic proof. That is a question about evidential weight, not a demonstration that the underlying value was false.
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