Falsely elevated urinary C-peptide during angiotensin receptor-neprilysin inhibitor therapy: A case report.
Akihiro Morishige, Mitsuaki Nishioka, Yoko Nakabayashi et al.
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Case in brief
A 54-year-old man with type 2 diabetes and hypertension was admitted for preoperative glycemic control after being diagnosed with aortic valve insufficiency. A clinical laboratory technologist identified a marked discrepancy between his urinary and serum C-peptide results. The patient was receiving an angiotensin receptor–neprilysin inhibitor (ARNI); after ARNI therapy was discontinued, his excreted urinary C-peptide decreased markedly. The authors considered the findings consistent with ARNI-related elevation of urinary C-peptide, potentially through suppression of C-peptide metabolism.
What made this case unusual
The key diagnostic pitfall was a marked urinary–serum C-peptide discrepancy during ARNI therapy, with urinary C-peptide falling markedly after the drug was stopped.
Diagnostic / clinical pearl
When urinary C-peptide is abnormally high and discordant with serum C-peptide, check for ARNI use and consider laboratory-guided retesting after discontinuation.
Why it matters
Prompt communication of discordant results by the clinical laboratory can help prevent misassessment of insulin secretion capacity.