Nondiabetic hypoglycemia may be caused by hepatic or renal failure, drugs, malnutrition, malignancy or functional changes. The fasting test may be used to distinguish organic hypoglycemia by insulinoma from functional (reactive) hypoglycemia. The aim was to compare if clinical and biochemical characteristics could clearly differentiate both diagnoses during fasting test.

In total, 84 patients (mean age 50 ± 16 years; 54 females) with history of unclear hypoglycemia were examined at our department in the last 8 years. Their liver and renal functions were normal. All patients underwent a 72-hour fasting test. The test was stopped earlier when neuroglycopenic symptoms developed. Blood samples were taken for glucose (BG), insulin (Ins) and C peptide measurements at the beginning, in 6-hour intervals and at the end of the test.

Fasting test was positive (F+ group) in 43 persons developing neuroglycopenic symptoms and thus it was stopped earlier (duration 24 ± 17 hours) as compared to F- group (41 persons) without these symptoms during the whole 72-hours of fasting. Both groups were similar in age, BMI or arterial pressure. Significant differences between F+ and F- group were observed at the end of the test (BG: 2.0 ± 0.4 vs. 3.8 ± 0.8 mmol/l, p<0.0001; Ins: 61 (11; 111) vs. 13 (5; 22) mU/L, p<0.0001; C peptide: 1.4 (0.5; 2.1) vs. 0.4 (0.1; 0.6) nmol/L, p<0.0001). All patients in F+ group developed spontaneous hypoglycemia <2.5 mmol/l during fasting but it was not true in F- group. The insulin/BG ratio (normal value <5.0 mU/mmol) could significantly distinguish both groups at the end of fasting (29.7 vs. 3.5 mU/mmol, p<0.0001). Insulinoma was then confirmed in all F+ patients at surgery.

Fasting test represents the most important diagnostic tool in the evaluation of unclear nondiabetic hypoglycemia. Neuroglycopenic symptoms together with spontaneous hypoglycemia by fasting are the most sensitive indicators of insulinoma. In addition, the insulin/BG ratio seems to be of highest benefit in distinguishing organic and functional hypoglycemia.


J. Skrha: Advisory Panel; Self; Boehringer Ingelheim International GmbH. Speaker's Bureau; Self; Lilly Diabetes. M. Prazny: Advisory Panel; Self; Abbott, AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Medtronic, Merck Sharp & Dohme Corp., Novo Nordisk Inc., Sanofi-Aventis, Takeda Pharmaceutical Company Limited. Board Member; Self; Bayer AG. Consultant; Self; Medtronic, Roche Diabetes Care. Speaker's Bureau; Self; Abbott, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Medtronic, Novartis Pharmaceuticals Corporation, Novo Nordisk Inc., Sanofi-Aventis, Servier, Teva Pharmaceutical Industries Ltd. J. Krizova: None. J. Skrha: Advisory Panel; Self; Boehringer Ingelheim International GmbH, Lilly Diabetes, Novo Nordisk A/S, Sanofi.



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