title: Sensitivity and reproducibility of urinary C-peptide as estimate of islet B-cell function in insulin-treated diabetes.
abstract: The aims of the present study were to evaluate the ability of urinary C-peptide determination to demonstrate presence of residual insulin secretion, and to evaluate the reproducibility of urinary C-peptide excretion in 125 insulin-treated diabetic patients. C-peptide was determined in two consecutive 24-h urine specimens and related to plasma C-peptide 6 min after the intravenous injection of 1 mg glucagon. The detection limit of C-peptide in plasma was defined analytically (greater than or equal to 0.02 nmol l-1) and from pancreatectomized patients (greater than or equal to 0.06 nmol l-1), and in urine only analytically (greater than or equal to 0.1 nmol l-1). If the analytical detection limit of plasma C-peptide was used as indicator of residual insulin secretion, islet B-cell function was preserved in all patients. In patients with stimulated plasma C-peptide levels from 0.02- less than 0.06 nmol l-1 no increase was found in plasma C-peptide values after stimulation with glucagon. This unresponsiveness of islet B-cells is in good agreement with the existence of a biological detection limit of C-peptide in plasma of 0.06 nmol l-1. Using this biological plasma C-peptide detection limit, 49 of 125 patients were without residual insulin secretion. In contrast to this, only 7 patients were diagnosed as C-peptide nonsecretors using the analytical detection limit of urinary C-peptide. Eighty-four per cent of patients considered to have Type 1 (insulin-dependent) diabetes with a duration of diabetes of more than 15 years had detectable C-peptide in the urine.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medical Department, Fredericia Hospital, Denmark.
authors.forename: H J
authors.initials: HJ
authors.lastname: Gjessing
authors.forename: L E
authors.initials: LE
authors.lastname: Matzen
authors.forename: O K
authors.initials: OK
authors.lastname: Faber
authors.forename: A
authors.initials: A
authors.lastname: Frøland
mesh_terms: D000293:Adolescent; D015415:Biomarkers / Q000652:urine*; D002096:C-Peptide / Q000097:blood / Q000652:urine*; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000188:drug therapy / Q000503:physiopathology / Q000652:urine*; D005215:Fasting; D005934:Glucagon; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D007118:Immunoassay; D007328:Insulin / Q000378:metabolism / Q000627:therapeutic use; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000503:physiopathology*; D008832:Microchemistry
chemical_list: D015415:Biomarkers; D002096:C-Peptide; D005934:Glucagon; D006442:Glycated Hemoglobin; D007328:Insulin