Assaying tumor necrosis factor concentrations in human serum. A WHO International Collaborative study

A collaborative study involving several international research groups was conducted in order to test the validity and reproducibility of tumor necrosis factor-alpha (TNF) measurements in serum. 58 serum samples, nine of them spiked with recombinant human TNF, were aliquoted and distributed blindly to 11 different laboratories. 20 samples were obtained from cerebral malaria patients, 20 from septic shock patients, eight from patients with rheumatoid arthritis and ten from normal blood donors. The serum samples were assayed for TNF using various immunoassays (ELISA), radioimmunoassays (RIA) and bioassays. Interassay coefficient of variance was analysed. Substantial differences were observed on terms of sensitivity and results obtained with the different commercial and in-house assays. The level of sensitivity was highest with ELISAs and bioassays. RIAs yielded the highest concentrations of TNF in the same samples as compared to those obtained by ELISAs and bioassays. These data emphasize the necessity of establishing international standards for cytokine assays in order to render the interpretation of biological and medical data more reliable.