Correlation between IL-6 levels and the systemic inflammatory response score: can an IL-6 cutoff predict a SIRS state?

BACKGROUND: Recently, increasing emphasis is being placed upon assessment of the inflammatory status of the patient. Serum inflammatory cytokines, particularly IL-6, have been used as an adjunct to this assessment. Another method uses a combination of simple laboratory and clinical data to provide an assessment of the patient's current level of systemic inflammation, the SIRS. The aim of this study was to investigate, in a group of adult trauma patients, the relationship between the interleukin-6 (IL-6) concentration, the systemic inflammatory response score (SIRS) and outcome.

METHODS: In patients with femoral shaft fracture, serum IL-6 levels and clinical parameters were recorded prospectively on admission and on days 1, 3, 5, and 7. Clinical course, the SIRS score and complications were documented. Nonparametric tests were used to assess relationships between variables and receiver operator characteristic (ROC) curves were used to examine their predictive values. Significance was assumed at the p < 0.05 level.

RESULTS: Forty-eight patients were included in the final analysis, with a median new injury severity score (NISS) of 31.5 (range, 9-75). The presence of a "SIRS state" detected early (day 1 and 3) positively correlated with the IL-6 measurement from the same period (p < 0.001). ROC curve analysis revealed elevated IL-6 to be significantly diagnostic of a SIRS state (p < 0.001) at all times. Early (days 0 and 1), an IL-6 value above 200 pg/dL diagnosed a SIRS state with an 83% sensitivity and a 75% specificity (area under ROC curve 0.76, p < 0.0001). Both a SIRS state and an IL-6 > 300 pg/mL was associated with a significantly increased risk of complication (pneumonia, MOF, death). Both systems were found to be significantly diagnostic of these complications using ROC curve analysis.

CONCLUSIONS: The IL-6 concentration and SIRS score are useful adjuncts to clinical evaluation of the injured patient. In the early phase, they are closely correlated with the NISS and each other. A cutoff value of 200 pg/dL was shown to be significantly diagnostic of a SIRS state. Significant correlations between adverse events and both the IL-6 level and SIRS state are demonstrated.