Serum eosinophil cationic protein determination in asthmatic children-effect of different collecting tubes used for blood sampling.

We compared the effect of using 2 different serum collecting tubes, serum separation tubes (SST, with clot activator and gel barrier) and conventional glass tubes (with no additives), on circulating levels of eosinophil cationic protein (ECP) in asthmatic children and controls. The serum ECP values obtained from both SST and glass tubes were significantly higher in asthmatic children than in corresponding controls. ECP values were higher in serum samples using SST than in those using glass tubes (P<0.01), while no difference was found between the two in controls. ECP levels correlated with peripheral eosinophil counts, for SST samples and glass tube samples alike. The difference in ECP levels between these two tubes also correlated with circulating eosinophil counts (r = 0.62, P = 0.004) After 18-hour storage at room temperature, the ECP values increased significantly in samples obtained from asthmatic children. No difference in ECP values between SST samples and glass tube samples was found for 18 hour samples. Thus, ECP levels obtained from SST samples and glass tube samples, though reliable, should not be directly compared, especially in asthmatic children with eosinophilia.