Standardization of C-peptide measurements

Randie R. Little, Curt L. Rohlfing, Alethea L. Tennill, Richard W. Madsen, Kenneth S. Polonsky, Gary L. Myers, Carla J. Greenbaum, Jerry P. Palmer, Eduard Rogatsky, Daniel T. Stein

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


BACKGROUND: C-peptide is a marker of insulin secretion in diabetic patients. We assessed within- and between-laboratory imprecision of C-peptide assays and determined whether serum calibrators with values assigned by mass spectrometry could be used to harmonize C-peptide results. METHODS: We sent 40 different serum samples to 15 laboratories, which used 9 different routine C-peptide assay methods. We also sent matched plasma samples to another laboratory for C-peptide analysis with a reference mass spectrometry method. Each laboratory analyzed 8 of these samples in duplicate on each of 4 days to evaluate within- and between-day imprecision. The same 8 samples were also used to normalize the results for the remaining samples to the mass spectrometry reference method. RESULTS: Within- and between-run CVs ranged from <2% to >10% and from <2% to >18%, respectively. Normalizing the results with serum samples significantly improved the comparability among laboratories and methods. After normalization, the differences among laboratories in mean response were no longer statistically significant (P = 0.24), with least-squares means of 0.93-1.02. CONCLUSIONS: C-peptide results generated by different methods and laboratories do not always agree, especially at higher C-peptide concentrations. Within-laboratory imprecision also varied, with some methods giving much more consistent results than others. These data show that calibrating C-peptide measurement to a reference method can increase comparability between laboratories.

Original languageEnglish (US)
Pages (from-to)1023-1026
Number of pages4
JournalClinical chemistry
Issue number6
StatePublished - Jun 1 2008
Externally publishedYes

ASJC Scopus subject areas

  • General Medicine


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