I agree, and would add that TNFa is very labile. You should therefore avoid freeze thaw cycles. Aliquot the samples if you think you may need to assay more than once. Even one thaw can refreeze will affect TNFa concentrations, as will prolonged storage at only -20oC.
Ok thanks. I saw protocol 10min at RT to coagulate the RBC well and then on ice. Wait until the whole set is done (everything on ice) and centrifugation step and run assay/ storage.