C-peptide represents the connecting peptide which is cleaved from proinsulin in the production of endogenous insulin. As such, the presence of C-peptide indicates endogenous production of insulin, whereas C-peptide is absent if only exogenous insulin is administered. For accurate interpretation in appropriate clinical settings, plasma C-peptide should be paired with laboratory plasma glucose (± insulin) testing. Depending on the clinical question, either fasting or non-fasting specimens may be appropriate.
In patients with diabetes, C-peptide may be of value in the assessment of residual pancreatic function in insulin treated diabetics, differentiating between types of diabetes (eg in presence of high or normal glucose, C-peptide is typically low or low-normal in Type 1 diabetes, but typically high in MODY or Type 2 diabetes).
In patients with hypoglycaemia, high C-peptide may be associated with insulinoma, dumping syndrome or sulphonylurea use, whereas low C-peptide is an appropriate physiological response representing less release of endogenous insulin. A 72 hour fast or mixed meal test may be performed in certain settings to provoke hypoglycaemia for this purpose and aid clinical diagnosis if it is not captured opportunistically.
It is suggested that an endocrinologist be consulted for further advice regarding interpretation.
C-peptide requests should be paired with a plasma glucose collected at the same time to ensure accurate interpretation. This may be either fasting or non-fasting, depending on the clinical question.
Paired C-peptide and glucose (±insulin) may be useful to differentiate between different types of diabetes. For this purpose either fasting or non-fasting samples are acceptable.
Paired C-peptide and glucose (±insulin) may also be useful to differentiate between different causes of hypoglycaemia, with fasting status depending on the situation where hypoglycaemia is present.
Transport to lab on water/ice slurry if haemolysis likely.
Ambient (8 - 24 degrees Celsius)
Transport to lab ambient for up to 5 days if no hemolysis, otherwise frozen.
350 – 750 pmol/L (fasting, BMI <25)
Roche Cobas e411
$42.65 (Exclusive of GST)
Measure glucose at the same time.
At room temperature, C-peptide is sensitive to hemolysis, and the rate of C-peptide loss increases with the degree of hemolysis. For example, at a level of 0.8g Hb/L, 10% of C-peptide is lost after 24 hours at room temperature.
C-peptide in plasma is not stable long-term at -20o. Loss is of the order of 2% per month. Stable at -40o or lower.
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