Editing C-peptide (section)

==Clinical uses of C-peptide testing==
Patients with diabetes may have their C-peptide levels measured as a means of distinguishing [[type 1 diabetes]] from [[Diabetes mellitus type 2|type 2 diabetes]] or [[maturity-onset diabetes of the young]] (MODY).<ref>{{cite journal | vauthors = Jones AG, Hattersley AT | title = The clinical utility of C-peptide measurement in the care of patients with diabetes | journal = Diabetic Medicine | volume = 30 | issue = 7 | pages = 803–17 | date = July 2013 | pmid = 23413806 | pmc = 3748788 | doi = 10.1111/dme.12159 }}</ref> Measuring C-peptide can help to determine how much of their own natural insulin a person is producing as C-peptide is secreted in equimolar amounts to insulin. C-peptide levels are measured instead of insulin levels because C-peptide can assess a person's own insulin secretion even if they receive insulin injections, and because the liver metabolizes a large and variable amount of insulin secreted into the [[portal vein]] but does not metabolise C-peptide, meaning blood C-peptide may be a better measure of portal insulin secretion than insulin itself.<ref>{{cite journal | vauthors = Clark PM | title = Assays for insulin, proinsulin(s) and C-peptide | journal = Annals of Clinical Biochemistry | volume = 36 | issue = 5 | pages = 541–64 | date = September 1999 | pmid = 10505204 | doi = 10.1177/000456329903600501 | doi-access =  | s2cid = 32483378 }}</ref><ref>{{cite journal | vauthors = Shapiro ET, Tillil H, Rubenstein AH, Polonsky KS | title = Peripheral insulin parallels changes in insulin secretion more closely than C-peptide after bolus intravenous glucose administration | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 67 | issue = 5 | pages = 1094–9 | date = November 1988 | pmid = 3053748 | doi = 10.1210/jcem-67-5-1094 }}</ref>  A very low C-peptide confirms Type 1 diabetes and insulin dependence and is associated with high glucose variability, hyperglycaemia and increased complications. The test may be less sufficient to diagnose or recognize a subgroup of type 1 diabetes named [[Latent autoimmune diabetes in adults|Latent autoimmune diabetes in adults (LADA)]], whose C-peptide levels may not be as low as those in typical Type 1 diabetes while may sometimes overlap with those seen in type 2 diabetes, and [[Beta cell|Beta-cell]] antibody testing is needed for better diagnosis in this case.<ref name=cmc>{{cite journal|last=R|first=Chandini |author2=Udayabhaskaran V |author3=Binoy J Paul |author4=K.P Ramamoorthy|title=A study of non-obese diabetes mellitus in adults in a tertiary care hospital in Kerala, India|journal=International Journal of Diabetes in Developing Countries|date=July 2013|volume=33|issue=2|pages=83–85|doi=10.1007/s13410-013-0113-7|s2cid=71767996 }}</ref><ref>{{Cite journal |last1=O'Neal |first1=Katherine S |last2=Johnson |first2=Jeremy L |last3=Panak |first3=Rebekah L |date=November 1, 2016 |title=Recognizing and Appropriately Treating Latent Autoimmune Diabetes in Adults |url=https://diabetesjournals.org/spectrum/article/29/4/249/32702/Recognizing-and-Appropriately-Treating-Latent |journal=Diabetes Spectrum |language=en |volume=29 |issue=4 |pages=249–252 |doi=10.2337/ds15-0047 |pmid=27899877 |pmc=5111528 |access-date=March 15, 2024 |archive-date=March 15, 2024 |archive-url=https://web.archive.org/web/20240315181746/https://diabetesjournals.org/spectrum/article/29/4/249/32702/Recognizing-and-Appropriately-Treating-Latent |url-status=live }}</ref>

C-peptide can be used for differential diagnosis of hypoglycemia. The test may be used to help determine the cause of hypoglycaemia (low glucose), values will be low if a person has taken an overdose of insulin but not suppressed if hypoglycaemia is due to an insulinoma or sulphonylureas.

Factitious (or factitial) hypoglycemia may occur secondary to the surreptitious use of insulin. Measuring C-peptide levels will help differentiate a healthy patient from a diabetic one.

C-peptide may be used for determining the possibility of [[gastrinoma]]s associated with Multiple Endocrine Neoplasm syndromes ([[MEN 1]]). Since a significant number of gastrinomas are associated with MEN involving other hormone producing organs (pancreas, parathyroids, and pituitary), higher levels of C-peptide together with the presence of a gastrinoma suggest that organs besides the stomach may harbor [[neoplasm]]s.

C-peptide levels may be checked in women with [[Polycystic Ovarian Syndrome]] (PCOS) to help determine degree of insulin resistance.

Ultrasensitive C-peptide assays have made it possible to detect very low levels of circulating C-peptide even in patients with longstanding [[Type 1 diabetes|type-1 diabetes]].<ref>{{cite journal |last1=Keenan |first1=Hillary A. |last2=Sun |first2=Jennifer K. |last3=Levine |first3=Jared |last4=Doria |first4=Alessandro |last5=Aiello |first5=Lloyd P. |last6=Eisenbarth |first6=George |last7=Bonner-Weir |first7=Susan |last8=King |first8=George L. |author-link8=George L. King |date=August 10, 2010 |title=Residual Insulin Production and Pancreatic β-Cell Turnover After 50 Years of Diabetes: Joslin Medalist Study |url=http://dx.doi.org/10.2337/db10-0676 |journal=Diabetes |volume=59 |issue=11 |pages=2846–2853 |doi=10.2337/db10-0676 |issn=0012-1797 |pmc=2963543 |pmid=20699420 |access-date=June 8, 2023 |archive-date=March 16, 2024 |archive-url=https://web.archive.org/web/20240316010114/https://diabetesjournals.org/diabetes/article/59/11/2846/15974/Residual-Insulin-Production-and-Pancreatic-Cell |url-status=live }}</ref> Studies have demonstrated that the presence of residual C-peptide in longstanding [[Type 1 diabetes|type-1 diabetes]] is associated with a lower risk for developing [[microvascular]] complications and a significant reduction in incidence of severe [[Hypoglycemia|hypoglycaemia]].<ref>{{cite journal |last1=Jeyam |first1=Anita |last2=Colhoun |first2=Helen |last3=McGurnaghan |first3=Stuart |last4=Blackbourn |first4=Luke |last5=McDonald |first5=Timothy J. |last6=Palmer |first6=Colin N.A. |last7=McKnight |first7=John A. |last8=Strachan |first8=Mark W.J. |last9=Patrick |first9=Alan W. |last10=Chalmers |first10=John |last11=Lindsay |first11=Robert S. |last12=Petrie |first12=John R. |last13=Thekkepat |first13=Sandeep |last14=Collier |first14=Andrew |last15=MacRury |first15=Sandra |date=February 5, 2021 |title=Erratum. Clinical Impact of Residual C-Peptide Secretion in Type 1 Diabetes on Glycemia and Microvascular Complications. Diabetes Care 2021;44:390–398 |url=http://dx.doi.org/10.2337/dc21er04b |journal=Diabetes Care |pages=dc21er04b |doi=10.2337/dc21er04b |pmid=33547206 |s2cid=237216616 |issn=0149-5992 |access-date=June 8, 2023 |archive-date=March 16, 2024 |archive-url=https://web.archive.org/web/20240316010117/https://diabetesjournals.org/CustomError |url-status=live |url-access=subscription }}</ref>