C-peptide analysis in serum is a laboratory test used to evaluate the level of insulin production in the body. C-peptide is a byproduct of insulin synthesis and is released from the pancreas when insulin is secreted. This test helps physicians diagnose and monitor conditions such as type 1 and type 2 diabetes, as well as assess states of insulin deficiency or excess. The test is performed by taking a blood sample, usually after fasting for 8 hours. The results are used to determine the pancreas’s ability to produce insulin and can therefore be used to evaluate treatment effectiveness and monitor patient response to different therapeutic options. C-peptide analysis is also a useful tool for distinguishing between type 1 diabetes, which is characterized by low insulin production, and type 2 diabetes, in which insulin production may be normal or elevated but accompanied by insulin resistance.