Erroneous C-Peptide Values Given?

Marshall B. Block, MD
Arch Intern Med. 1982;142(1):201. doi:10.1001/archinte.1982.00340140203042.
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To the Editor.  —A letter regarding permanent remission of ketotic diabetes with subsequent normal C-peptide secretion was published in the Archives (1981;141:960-961) by Harstine and co-workers. Their data for C-peptide in their table and their contention that the patient had subsequent normal values for this polypeptide are probably erroneous if the serum used for the C-peptide tests was not first cleared of insulin antibodies that, no doubt, would have arisen from the patient's previous insulin therapy. Since these antibodies would cause retention of proinsulin in the patient's plasma, cross-reactivity in the C-peptide assay would, therefore, accrue, with elevated levels of C-peptide ultimately being detected.1 Normal basal C-peptide levels are usually 0.75 ng/mL, or thereabouts, and the elevated basal levels noted in their patient bespeak some technical problem, if not an abnormality, in insulin secretion. Their comment on this point would be greatly appreciated and would help clarify what is


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