"Method-specific" stability of serum C-peptide in a multicenter clinical study

A Central laboratory that participates in multicenter clinical studies must consider and study the parameters that condition the in vitro stability of the analytes. We evaluated the effect of temperature on serum C-peptide storage during transport from clinical research centers to the Central laboratory. In particular, the stability for storage lengths from 0 to 24-48 hours at temperatures of between -20 degrees C and +37 degrees C were studied: the C-peptide assay was performed by means of a chemiluminescence and a RIA method. The tests confirmed that sample freezing is the gold standard for accurate determination of serum C-peptide and that storage at 37 degrees C may decrease the analyte levels. Instead, C-peptide stability at 2-8 degrees C appeared "method-specific"; while no apparent alteration was obtained with the chemiluminescence method up to 24 hours of storage, the RIA showed an early slight increase in C-peptide that is proportionate to storage time. Our work highlights that before starting up a multicenter clinical study it is always necessary to optimize and standardize biological sample storage and transport conditions to guarantee a high quality sample for analysis. Beyond this, it is even very useful to check the reliability of technical and instrumental resources that the Central laboratory will use during the study because molecular alterations of the analytes due to variable storage conditions can cause misleading results.