LEARNING OBJECTIVES: 1. To illustrate clinical features of hypoglycemia from inadvertent administration of a sulfonylurea compared to an insulinoma. 2. To demonstrate the importance of carefully reviewing medications that patients with hypoglycemia are taking. CASE INFORMATION: Two patients were referred for recurrent episodes of hypoglycemia thought to be due an insulinoma. The clinical presentations were characterized by precipitous drops in blood glucose (BG) associated with marked adrenergic symptoms. The first patient was a 69 yo man with a coronary artery disease, heart failure, hypertension, chronic renal insufficiency, and peripheral vascular disease. He had recurrent acute hypoglycemic reactions (including 3 hospital admissions) accompanied by adrenergic symptoms. He also had a recent myocardial infarction. Medications included warfarin, metoprolol, nifedipine, isosorbide dinitrate (IsoD), furosemide, famotidine, lisinopril, potassium, pentoxyphylline, and colchicine. His chemistry panel was normal. Prior workup included normal cortrosyn stimulation test and abdominal CT scan, and negative serum sulfonylurea levels. A 36 hour fast ( the patient refused to go beyond 36 hours) showed a BG of 59 mg/dl, a corresponding cpeptide of 3.5 ng/ml (0.7±3.0) , and absent insulin antibody. Inspection of his medications revealed a bottle labeled for IsoD contained two types of light green pills: IsoD and glyburide 5 mg. The second patient was an 87 yo woman who was referred for surgical treatment for a presumed insulinoma. Over a 2 mo period she has had several episodes consisting of confusion, diaphoresis, and syncope with confirmed hypoglycemia(BG levels < 40mg/dl). Medications included cardizem, ranitidine, acetaminophen, and diazepam. Evaluation included a normal chemistry panels, somatomedin, and cortrosyn stimulation test. Serum insulin and c-peptide levels at the time of hypoglycemia (BG= 37 mg/dl) were 36.38 pmol/L and 1600 pmol/L respectively. Serum and urine SFU screens were negative. CT and octreotide scans of the abdomen showed no abnormalities. Identification of the patient's home medications was done. In a bottle labeled diazepam were light blue-green tablets identified as generic glyburide 5mg. To further confirm SFU induced hypoglycemia, a repeat 72 hour fasting was done. At a glucose level of 94mg/dl, the insulin and insulin antibody levels were 3.2uU/ml (4.0±24.0) and < 5 % respectively, and at a glucose level of 58mg/dl, the levels were < 2 uU/ml and < 5% respectively. An exploratory laparotomy was canceled. In each case, no further hypoglycemic episodes occured following discontinuation of the SFU. DISCUSSION: The biochemical features of hypoglycemia due to sulfonylureas and insulinomas are similar. Insulinomas are commonly associated neuroglycopenic symptoms that are insidious in onset, and recipitous hypoglycemia with adrenergic symptoms is uncommon. Presence of such symptoms mandates a search for other causes. SFU-induced hypoglycemia may mimic an insulinoma biochemically. Our two cases illustrate the importance of careful attention to history, and a thorough inspection of all medications in patients presenting with hypoglycemia before extensive, diagnostic tests, including invasive procedures or surgery are undertaken LEARNING OBJECTIVES: 1) Diagnose chronic lung disease in patients with sickle cell disease.