Unreliable Insulin Test Casts New Doubts on Lucy Letby Conviction

A recent report from a consortium of pediatric and toxicology experts has raised serious concerns over the reliability of the insulin tests central to Lucy Letby’s conviction, prompting renewed calls for a full appeal. The case, which has already ignited significant public debate, is now under fresh scrutiny as experts question the forensic standards employed during Letby’s trial.

New Evidence and Forensic Concerns

The report, submitted to Britain’s Criminal Cases Review Commission by Letby’s legal team, presents evidence suggesting that the insulin test used—the Roche immunoassay—may have produced “falsely high insulin results.” This testing method, the experts argue, did not adhere to acceptable forensic standards, thereby undermining its reliability in establishing exogenous insulin administration in the case. The report focuses in particular on two infants, referred to as Babies F and L, who exhibited episodes of hypoglycemia yet recovered without further complications.

Lucy Letby, a former nurse at a northern England hospital’s neonatal unit, was convicted in 2023 of inflicting harm and, in seven instances, murdering infants through methods that allegedly included insulin poisoning. Her conviction, based in part on the disputed test results, has been a subject of intense debate since the verdict was handed down. More detailed coverage on the trial and its aftermath was provided in a New York Times article.

Examining the Forensic Evidence

The panel of experts, which includes a half-dozen pediatric doctors and toxicology specialists, contend that the insulin test’s limitations were not adequately considered during the trial. They highlighted that the assay used is known to yield unreliable results, especially when applied to samples from neonates. The experts emphasize that the test should have been corroborated with more precise laboratory analyses before being used as a basis for conviction.

In their detailed report, the experts wrote, “Studies in adults and older children were quoted which are not relevant, and the limited appropriate information was not referred to.” Their assessment indicates that not only was the choice of data problematic, but the failure to consider alternative explanations for the hypoglycemic episodes further compromised the integrity of the prosecution’s case.

Implications for the Appeal and Broader Legal Debate

Critics of the trial point out that the testing protocol, as outlined in guidance from the Royal Liverpool Hospital laboratory, clearly states that the assay is “not suitable” for investigating hypoglycemia resulting from insulin injections. This guidance recommends that if exogenous insulin is suspected, the sample should be sent for external analysis. In the case of Babies F and L, however, the samples were never referred for further testing as both infants recovered.

The report also raises the possibility that the hypoglycemia could have arisen from alternative medical conditions such as line failure, sepsis, or perinatal stress-induced hyperinsulinism—possibilities that were not explored during the trial. A separate, comprehensive 698-page examination led by Canadian neonatologist Dr. Shoo Lee further scrutinized Letby’s case, concluding that there was no medical evidence to substantiate claims of deliberate harm in any of the 17 cases reviewed. Additional insights from Dr. Lee’s panel were previewed in February and have added momentum to the push for a renewed appeal.

Legal representatives for Letby, including her lawyer Mark McDonald, have argued that the accumulation of independent expert evidence necessitates an urgent review by the Court of Appeal. In a recent statement, Mr. McDonald asserted, “The conclusions of the report on Babies F and L clearly demonstrate that the case must go back to the Court of Appeal as a matter of urgency.” He further emphasized that “Lucy Letby is currently serving 15 whole life terms in prison, when overwhelming independent expert evidence indicates that no babies were murdered.” More details on the perspectives of families affected by the events were documented in a public inquiry submission.

While the report and its associated findings have rekindled debate over the forensic methods used in the trial, they also underscore the complexities inherent in diagnosing and interpreting biochemical data in vulnerable populations. As the case awaits further legal proceedings, the spotlight remains on the standards of evidence required in forensic testing, particularly when the stakes involve irreversible life sentences.

The controversy surrounding the insulin test not only challenges the judicial process in Letby’s case but also raises broader questions about the adequacy of forensic protocols in cases involving neonatal care. The call for rigorous, transparent, and methodologically sound testing has resonated widely among legal experts, medical professionals, and progressive advocates alike.

As the Criminal Cases Review Commission continues its investigation into potential miscarriages of justice, the evolving narrative around Lucy Letby’s trial serves as a potent reminder of the need for precision and accountability in the administration of both medical and judicial practices.