HealthRX.com · Printable lab tracker
C-peptide draw record: medicines, timing and the sample
Fill this in before and on the day of a C-peptide test: why it was ordered, every medicine that changes insulin release with the time of the last dose, and the conditions of the sample. Take it to the draw and to the results visit.
Why the test was ordered
The question it should answertype of diabetes, low blood sugar episodes, whether insulin is needed, other
Ordering clinician
Fasting or after food?hours since you last ate
Medicines that change insulin or glucose
Change or hold a dose only if the person who ordered the test tells you to.
| Medicine | Dose | How often | Last dose: date and time | Held for the test? (only if told) | Written on the lab form? |
|---|---|---|---|---|---|
| Insulin (which kind) | |||||
| Sulfonylurea or meglitinide | |||||
| GLP-1 or GIP/GLP-1 injection | |||||
| Steroid tablets or injections | |||||
| Octreotide, lanreotide or diazoxide | |||||
The sample
Date and time drawn
Blood glucose on the same sample
Latest eGFR or creatinine, and its date
C-peptide result, with unitsng/mL or nmol/L
The lab's reference range
Points from MedlinePlus, the labels and the review
- MedlinePlus: you may need to fast for 8 to 12 hours before a C-peptide blood test.[1]
- MedlinePlus: what the result means depends on the medicines you take and on other tests, such as blood glucose.[1]
- Nateglinide before a meal: the insulin rise peaks at about 1 hour and is back to baseline by 4 hours.[2]
- Glipizide XL releases the drug over 24 hours, and its label says meal-time C-peptide responses stay enhanced after at least 6 months.[3]
- The Proglycem label says diazoxide causes a false-negative insulin response to glucagon.[4]
- Low glucose suppresses insulin and C-peptide, and C-peptide can read falsely high with kidney impairment; a glucose above 8 mmol/L marks a stimulated sample in the review.[5]
For the clinician who ordered the test
- Should I take my morning medicines before or after the blood draw?
- Which of my insulin doses, if any, should change before the test?
- Will glucose be measured on the same sample?
- Is my latest kidney test recent enough to read this result?
- Would a test after a meal or after glucagon answer the question better?
- If the result does not fit, how and when should it be repeated?
Sources for the facts on this sheet
- U.S. National Library of Medicine. C-Peptide Test: MedlinePlus Medical Test. Accessed 2026-10-19. https://medlineplus.gov/lab-tests/c-peptide-test/
- Dr. Reddy's Laboratories Limited, via DailyMed. Nateglinide tablets, for oral use: prescribing information. Effective 2021-11-27. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f7b28951-76d2-cabd-64a1-b74aa225c6e9
- Roerig, via DailyMed. Glucotrol XL (glipizide) extended release tablets, for oral use: prescribing information and patient information. Effective 2026-07-21. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=eed99b60-d043-4249-9b2a-f05e46fb588d
- Teva Pharmaceuticals USA, Inc., via DailyMed. Proglycem (diazoxide) oral suspension: prescribing information. Effective 2026-10-06. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b16c7832-2fd9-49af-b923-1dc0d91fd6e2
- Jones AG, Hattersley AT. The clinical utility of C-peptide measurement in the care of patients with diabetes. Diabet Med 2013. PMID 23413806. https://pubmed.ncbi.nlm.nih.gov/23413806/
This sheet records information for a conversation with your prescriber or pharmacist. It does not replace their instructions or the medication's prescribing information.