Hi I wanted to standardize protocol for VEGF ELISA from cell culture supernatant,previously western blot did not work in my lab,can u send me the protocol for VEGF ELISA is any any means by which I can improve my assay by concentrating VEGF plz help

Concentrating chemokines and growth factors like VEGF usually leads to considerable losses due to adsorption, denaturation etc (CentriCon, SpeedVac techniques). Some of them can be lyophilized, but thats very cumbersome esp if you are doing 96-well plate based assays.
Your best bet is to get a good Ab-pair for sandwich-ELISA - RnD systems has the duoset range of matched Ab pairs: they should have one for both mouse and human VEGF.