Background: Cytokines signal the normal processes of inflammation and repair in all organs, yet the aberrant expression of these peptide mediators is associated with significant organ dysfunction. The accurate measurement of cytokines is therefore critical. In this study, we sought to investigate the alterations in cytokine expression early after trauma in humans using a new competitive binding immunoassay that measures both free and bound cytokine 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. Exclusion criteria were transfers, death within 24 hours, pregnancy, known acquired immunodeficiency syndrome, chemotherapy, transplant, or other chronic immune disorder. "Total" cytokine immunoassay was compared with ELISA for cytokines (interleukin [IL]-1, IL-6, and IL-10) measured in serum.
Results: Cytokine concentrations measured by total immunoassay were significantly higher (10- to 500-fold increase) than those measured by ELISA, and correlation between the two methods was poor (r2 = 0.193 for IL-10). No significant differences in mean serum cytokine concentrations were noted between 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 contrast, 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 normal controls using total cytokine immunoassays.
Conclusion: Cytokine measurements in peripheral blood in trauma patients and normal controls are significantly (10- to 500-fold) higher when using a total cytokine assay that measures both free and bound cytokine. Competitive immunoassays may be the method of choice when measuring endogenous cytokine levels in biologic fluids, and new normal ranges for cytokines must be established for future accurate research in critical care and trauma.