Objective: To examine whether transfer from animal insulin to human insulin is associated with an increased risk of severe hypoglycaemia.
Design: Matched case-control study of insulin treated diabetic patients admitted to hospital because of hypoglycaemia during 1984-7, the period when human insulin was introduced into treatment.
Setting: Case admissions and control admissions were obtained from eight public hospitals within the Swiss canton of Berne and a second control group comprised members of the Bernese section of the Swiss Diabetes Association.
Subjects: 94 patients with insulin treated diabetes with a total of 112 admissions for hypoglycaemia during 1984-7 (case admissions), 182 patients with insulin treated diabetes seen in the same hospitals for reasons other than hypoglycaemia with a total of 225 admissions (control admissions), and 86 insulin treated diabetic patients who were members of the Bernese section of the Swiss Diabetes Association.
Main outcome measures: Type of insulin used at time of admission, glycaemic control as measured by amount of glycated haemoglobin or glucose concentration; severity of hypoglycaemia.
Results: Treatment with human insulin at admission was more common in cases than controls (52/112 (46%) admissions v 77/225 (34%); p = 0.003). 116 out of 129 (90%) of admissions taking human insulin had been transferred from animal insulin, mainly because of non-availability of porcine insulins. The ratio of rate of hypoglycaemia in those taking human insulin to the rate in those taking animal insulin was 2.4 (95% confidence interval 1.3 to 4.4). Other risk factors for hypoglycaemia were a history of hypoglycaemic coma (rate ratio of history to no history 3.8, 2.3 to 6.4) and good glycaemic control (rate ratio of good to poor control 3.9, 1.4 to 7.5). With multivariate analysis the increase in rate ratio associated with use of human insulin rose to 3.0 (1.4 to 6.4). Comparison with the diabetes association controls also showed an increased risk associated with use of human insulin (2.2; 1.1 to 4.8).
Conclusions: Transfer of treatment from animal insulin to human insulin was associated with an increased risk of severe hypoglycaemia. Caution should be exercised when transferring diabetic patients to human insulin. Further studies are required to elucidate why this effect occurs.