The new evidence seen by Panorama shows a blood test from a third baby being cared for by Letby in November 2015 also recorded very high levels of insulin and low levels of C-peptide.
Lab results indicated the insulin level was in excess of 6,945 picomoles per litre – a very high reading. Had the insulin been natural, the C-peptide level would have been between 35,000 and 70,000, but the blood test showed it was just 220.
At the time, consultants on the neonatal unit assumed the insulin must be natural. Tests later revealed the baby had congenital hyperinsulinism (CHI) – a condition where the body naturally produces too much insulin.
But four experts have told Panorama that CHI could not explain such an exceptionally high insulin reading for the infant – partly because of the low C-peptide level, but also because a baby with CHI would never produce that much insulin.
Medical records seen by Panorama show how quickly the boy became poorly after Letby came on duty. A blood test taken at 06:56 showed the infant had a normal blood sugar level of three millimoles per litre (mmol/L).
Letby started her shift at 08:00, and by 13:54 his blood sugar level had plummeted to one mmol/L – a dangerously low level, and a strong indication the baby had too much insulin.
The boy’s blood sugar level remained low throughout the nurse’s shift and he only recovered after she went off duty at 20:00.
