Mrs B., 39 years old, hospitalized in the department of respiratory medicine for lung cancer, has an undetectable and verified venous blood glucose concentration (measured in central laboratory) less than 0.1 mmol/L. The patient feels no symptom of hypoglycemia. A concomitant capillary determination realised by a bedside glucose reader gives a result of 4.7 mmol/L. This gap is due to glucose consumption in vitro by leukocytes between the time of sampling and laboratory analysis. Indeed the leukocyte count is 86.4 G/L (92% neutrophils) probably in a context of paraneoplastic syndrome. An efficient talk between biologist and clinician identified this phenomenon for this patient. This event allows us to recall the different causes of hypoglycemia (artifactual or real), and to describe the care of patients with true hypoglycemia.