Why he matters in this case
The Crown’s case on the insulin counts (Babies F and L) rested on a single Roche Cobas immunoassay reading that showed high insulin with low C-peptide. The prosecution told the jury that this pattern could only be explained by exogenous insulin. Dr Ismail’s published career has been about demonstrating that this is not true: the Roche immunoassay is well-known in clinical biochemistry to produce false positives in the presence of interfering antibodies, and in a range of other clinical circumstances that are not unusual in neonates.
Professional background
- Consultant clinical biochemist in the NHS.
- Author of peer-reviewed publications on immunoassay interference, analytical false-positive rates, and the specific problem of macro-insulin and insulin auto-antibodies.
- Contributor to clinical-laboratory guidance on when an immunoassay reading is and is not sufficient for a forensic conclusion.
His position on the Letby insulin evidence
Dr Ismail’s published commentary on the Letby insulin evidence makes the following core points:
- The Roche Cobas immunoassay is not, and was never marketed as, a forensic test for exogenous insulin. The manufacturer’s protocol requires confirmation by mass spectrometry.
- Insulin auto-antibodies (transiently acquired in utero from a diabetic mother, or chronically present from other causes) interfere with the Roche assay and produce a pattern indistinguishable from exogenous insulin.
- Several other clinical conditions — sepsis, adrenal suppression, liver or kidney disease, specific drug exposures — can all produce false-positive results.
- The specific sample-handling protocols required for forensic use were not applied. Gel-tube collection, delayed centrifugation, and storage at ambient temperature are all sufficient, on their own, to compromise the reading.
- The numerical insulin value reported is implausibly high on the Crown’s own theory of a 0.6 ml spike of insulin into a slow-running TPN bag.
What this means for the convictions
The insulin counts are not incidental to the rest of the case. The Crown’s closing speech framed them as the most concrete and hardest-to-dispute evidence on the indictment — “you cannot argue with a lab result,” in effect. Dr Ismail’s point is that you can and must argue with this particular lab result, because it was a screening result interpreted as though it were a forensic result, and those are not the same thing.
The 2025 Joint Expert Witness Insulin Report on Babies F and L drew on Dr Ismail’s framework.