Total cytokine immunoassay: A more accurate method of cytokine measurement?

Background: Cytokines signal the normal processes of inflammation and repai r in all organs, yet the aberrant expression of these peptide mediators is associated,vith significant organ dysfunction, The accurate measurement of cytokines is therefore critical. In this study, we sought to investigate th e alterations in cytokine expression early after trauma in humans using a n ew competitive binding immunoassay that measures both free and bound cytoki ne and compare this with standard enzyme-linked immunosorbent assay (ELISA) , which measures only Free cytokine. Methods: Peripheral blood was obtained from trauma patients at admission. E xclusion criteria were transfers, death within 24 hours, pregnancy, known a cquired immunodeficiency syndrome, chemotherapy, transplant, or other chron ic immune disorder. "Total" cytokine immunoassay was compared with ELISA fo r cytokines (interleukin [IL]-1, IL-6, and TL-IO) measured in serum. Results: Cytokine concentrations measured by total immunoassay were signifi cantly higher (10- to 500-fold increase) than those measured by ELISA, and correlation between the two methods was poor (r(2) = 0.193 for IL-10). No s ignificant differences in mean serum cytokine concentrations were noted bet ween trauma patients and normal controls for IL-1 (56 vs. 37 pg/mL), IL-6 ( 16 vs. 25 pg/mL), and IL-10 (4 vs. 26 pg/mL) using the ELISA method. In con trast, trauma patients had significantly higher serum concentrations of IL- 1 (3,320 vs. 1,470 pg/mL, p < 0.05), IL-6 (2,415 vs. 1,048 pg/ml,p < 0.05), and IL-10 (2,307 vs. 1,480 pg/mL, p < 0.05) at admission compared with nor mal controls using total cytokine immunoassays. Conclusion: Cytokine measurements in peripheral blood in trauma patients an d normal controls are significantly (10- to 500-fold) higher when using a t otal cytokine assay that measures both free and bound cytokine, Competitive immunoassays may be the method of choice when measuring endogenous cytokin e levels in biologic fluids, and new normal ranges for cytokines must be es tablished for future accurate research in critical care and trauma.