c-peptide and Anemia--Sickle-Cell

The work-up of fasting hypoglycemia may be difficult but is crucially important because a wrong diagnosis can lead to either unnecessary pancreatectomy or a missed pancreatic tumor. We describe a patient with severe fasting hypoglycemia [22-32 mg/dl (1.2-1.8 mmol/liter) after 6-10 h of fasting] in which the diagnosis of a secretory islet-cell tumor was obscured, rather than facilitated, by use of a new, highly specific serum insulin assay. Insulin measured by the specific assay suppressed normally during fasting hypoglycemia [undetectable at < 2.0-3.8 micro IU/ml (26.4 pmol/liter)], whereas insulin measured by older, less specific assays was diagnostically elevated [34, 73 micro IU/ml (236.1, 507.0 pmol/liter)]. Serum proinsulin and C-peptide levels were abnormal, and further work-up revealed an islet-cell tumor that secreted predominantly proinsulin. The tumor was surgically removed, relieving the fasting hypoglycemia. We conclude that insulin levels as measured by new, highly specific insulin assays may obscure the diagnosis of a functional, proinsulin-secreting islet-cell tumor. Because proinsulin cross-reacts with insulin in older insulin assays, C-peptide or proinsulin should be measured to rule out a proinsulin-secreting islet-cell tumor. Normative values for new insulin assays must be established during prolonged fasting.

Topics: Adenoma, Islet Cell; Adult; Anemia, Sickle Cell; Biopsy, Needle; C-Peptide; Fasting; Humans; Hypoglycemia; Insulin; Male; Pancreatectomy; Pancreatic Neoplasms; Proinsulin; Sensitivity and Specificity; Ultrasonography

Intravenous glucose tolerance tests (IVGTT) were performed on 9 adults with sickle cell anemia and 15 normal controls. Blood samples were collected before and 1, 3, 5, 10, 20, 30, 40, 50, and 60 min after intravenous glucose infusion and used for glucose and C-peptide assays. The mean C-peptide concentration after glucose infusion was significantly (p less than 0.05) lower for the SCA patients as compared to the controls. No significant differences were observed in the glucose concentration of IVGTT between the two groups. These results suggest an inadequate insulin secretion by the endocrine pancreas in sickle cell anemia or an independent genetic abnormality in linkage disequilibrium with the beta s gene.

Topics: Adolescent; Adult; Anemia, Sickle Cell; Blood Glucose; C-Peptide; Female; Humans; Insulin; Insulin Secretion; Male