{"id":"c-peptide","name":"C-Peptide","shortName":"C-Peptide","aliases":["Connecting Peptide","C-Peptide, Serum","C-PEPTIDE, FASTING","Insulin C-Peptide","C Peptide","Serum C-Peptide","Serum, C-Peptide","C-Peptide Connecting Peptide of Insulin","C-Peptide, Random"],"abbreviations":["C-pep"],"loinc":[{"code":"1986-9","primary":true},{"code":"14633-2","primary":false},{"code":"35195-7","primary":false},{"code":"42180-0","primary":false}],"specimen":"serum-or-plasma","units":[{"ucum":"ng/mL","display":"ng/mL"},{"ucum":"nmol/L","display":"nmol/L"},{"ucum":"pmol/L","display":"pmol/L"}],"referenceRanges":[{"population":"Adults","low":0.8,"high":3.85,"unit":"ng/mL","unitDisplay":"ng/mL","note":"Quest Diagnostics' fasting interval (immunoassay, 12-hour fast): 0.80 to 3.85 ng/mL (about 0.26 to 1.27 nmol/L). Intervals differ between labs and assays: Labcorp prints 1.1 to 4.4 ng/mL, ARUP 0.5 to 3.3 ng/mL and the ABIM January 2026 list 0.8 to 3.1 ng/mL, and all of these apply to fasting samples. C-peptide normally rises well above this after a meal, so a non-fasting result should not be judged against it. Read it together with a glucose measured at the same time.","sources":[{"title":"C-Peptide (test code 372)","url":"https://testdirectory.questdiagnostics.com/test/test-detail/372/c-peptide?cc=MASTER","publisher":"Quest Diagnostics"},{"title":"C-Peptide (test 010108)","url":"https://www.labcorp.com/tests/010108/c-peptide","publisher":"Labcorp"},{"title":"Serum, C-Peptide (test 0070103)","url":"https://ltd.aruplab.com/Tests/Pub/0070103","publisher":"ARUP Laboratories"},{"title":"ABIM Laboratory Test Reference Ranges (January 2026)","url":"https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf","publisher":"American Board of Internal Medicine","year":2026}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"C-peptide is released along with insulin, so it shows how much insulin your own pancreas is making, even if you take insulin.","url":"https://bloodtesttracker.com/markers/c-peptide","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}