I’m endocrine fellow who proceed this project. I collected all blood samples from newly diagnosed obese children. The blood samples were stored about 1-2 hr at 4 ºC temperature before serum collection. All serum were collected by 1000 g centrifuge at 25ºC temperature in 20 minutes followed by CUSABIO serum collection for GPC4 method. After that all were immediatly frozen at -80ºC temperature about 1-6 months before processing GPC4 ELISA test.
Therefore, we found that the difference duration of collected serum were clearly no effect to undetectable GPC4 results. Because the most recently serum was showed undetectable GPC4 result. Moreover, I checked the reproducible of your kit. All GPC4 results of the same samples were difference about 1-2 times; some couldn’t be detected in one kit but could be detected in another.