Factitious hypoglycaemia documented by a modified assay for the measurement of plasma sulphonylurea

Screening for Sulphonylureas in the Investigation of Hypoglycaemia

The most important cause of hypoglycaemia in the presence of high insulin and C-peptide concentrations is insulinoma. However, a similar picture arises from use of sulphonylureas, which is sometimes covert. All specimens received in two years by a supraregional assay service laboratory from adults with low glucose and inappropriately high insulin and C-peptide concentrations were tested for sulphonylureas by a radioimmunoassay that employed antibodies to glibenclamide. In sulphonylurea-positive cases a questionnaire was sent to the consultant responsible for the patient, to elicit further information.

Samples from 93 adult patients met the criteria, and 34 (37%) of these gave a positive result on screening for sulphonylureas. The consultants provided further information on 31 of the 34, and in 20 the presence of a sulphonylurea was unexpected. In 10 the features were such as to raise the possibility of factitious drug ingestion.

A simple screening technique applied to specimens from patients with hyperinsulinaemic hypoglycaemia indicated that, in a substantial proportion of cases, the patient was taking a sulphonylurea.

Insulin & C-peptide levels in sulfonylurea-induced hypoglycemia: a systematic review

OBJECTIVES

We will describe insulin and C-peptide levels observed in sulfonylurea-induced hypoglycemia and determine whether these levels differed if obtained before or after hypoglycemic therapy.

METHODS

We performed a systematic review of the English literature to identify Medline articles containing "sets" (glucose <60 mg/dL with insulin and C-peptide levels). These "sets" were categorized as being obtained BEFORE, AFTER, or UNKNOWN with respect to hypoglycemic therapy.

RESULTS

22 articles, 76 patients, and 97 "sets" were included. Mean glucose (mg/dL), insulin (muIU/mL), and C-peptide (ng/mL) for all "sets' were 28.6 (+/-12.6; 26.1 to 31.2), 54.4 (+/-126.3; 28.3 to 80.5), 7.2 (+/-6.2; 5.9 to 8.5). The BEFORE measures were 24.3 (+/-7.3; 18.7 to 30.0), 36.6 (+/-26.2; 16.5 to 56.7), 5.4 (+/-4.6; 1.5 to 9.2). The AFTER measures were 33.1 (+/-9.8; 28.2 to 38.0), 126.7 (+/-278.1; 0 to 265.0), 10.3 (+/-10.5; 5.1 to 15.4). The UNKNOWN measures were 28.0 (+/-13.5; 24.7 to 31.3), 37.1 (+/-21.8; 31.7 to 42.5), 6.5 (+/-4.3; 5.4 to 7.6). Only one "set" (glucose 49 mg/dL) had insulin <3.9 muIU/mL and C-peptide <1.4 ng/mL.

CONCLUSIONS

Insulin > or =3.9 muIU/mL, C-peptide > or =1.4 ng/mL, and glucose <49 mg/dl are consistent with sulfonylurea-induced hypoglycemia. BEFORE levels were lower, but they were consistent with sulfonylurea-induced hypoglycemia.

Screening for sulphonylureas in the investigation of hypoglycaemia

The most important cause of hypoglycaemia in the presence of high insulin and C-peptide concentrations is insulinoma. However, a similar picture arises from use of sulphonylureas, which is sometimes covert. All specimens received in two years by a supraregional assay service laboratory from adults with low glucose and inappropriately high insulin and C-peptide concentrations were tested for sulphonylureas by a radioimmunoassay that employed antibodies to glibenclamide. In sulphonylurea-positive cases a questionnaire was sent to the consultant responsible for the patient, to elicit further information. Samples from 93 adult patients met the criteria, and 34 (37%) of these gave a positive result on screening for sulphonylureas. The consultants provided further information on 31 of the 34, and in 20 the presence of a sulphonylurea was unexpected. In 10 the features were such as to raise the possibility of factitious drug ingestion. A simple screening technique applied to specimens from patients with hyperinsulinaemic hypoglycaemia indicated that, in a substantial proportion of cases, the patient was taking a sulphonylurea.

Deliberate sulphonylurea poisoning mimicking hyperinsulinaemia of infancy

A 6 month old child presenting with seizures was found to be hypoglycaemic secondary to hyperinsulinism. A family history of type II diabetes prompted estimation of sulphonylurea in the baby's blood, which was found to be high. A multidisciplinary case conference concluded that the sulphonylurea ingestion was likely to be the result of Munchausen syndrome by proxy. When investigating hypoglycaemia of infancy this possibility should be considered.

Standardized procedure for the assay and identification of hypoglycemic sulfonylureas in human plasma

A standardized procedure for the assay and identification of hypoglycemic sulfonylureas in plasma is presented. External standards and plasma extracts containing glibenclamide, gliquidone, glipizide, or gliclazide were examined by high-performance liquid chromatography. The four sulfonylureas could be identified and measured with a precision of 5%-7% and a limit of detection close to 1-2 ng in injected external standards and 10-40 ng/ml in plasma samples. This method is suitable to study the pharmacokinetics of hypoglycemic sulfonylureas, for blood drug monitoring in diabetic patients, for diagnostic purposes in factitious hypoglycemia, and in cases relevant to forensic medicine.