Cytometric Bead Array to Measure Six Cytokines in Twenty-Five Microliters of Serum

Infections and sepsis are among the most common reasons for neonatal morbidity and mortality. Early diagnosis is difficult because clinical presentation is highly variable and signs are often subtle and common to a variety of conditions. Among the proposed early indicators of infection and sepsis are serum concentrations of interleukin (IL)-6, IL-8, and IL-10. It is believed that IL-8 is a sensitive indicator of infection and that high concentrations of IL-6 and IL-10 are indicators of sepsis and predictors of mortality (1)(2)(3). The concentrations of each of these cytokines in serum vary by several orders of magnitude (1)(2)(3). Literature-reported cutoff values for IL-8 are >70 ng/L (2) or >18 ng/L (1) for infection, and values >10 000 ng/L have been reported (1). IL-6 >175 ng/L is predictive of sepsis, and values >747 ng/L are predictive for pneumonia (3). IL-6 is also believed to be predictive of necrotizing enterocolitis (3). IL-10 >420 ng/L correlates with neonatal death (3). The ELISAs commonly used for cytokine detection require 50–100 μL of serum (∼100–200 μL of peripheral blood in the neonate) per cytokine. To determine the stage of an infection, measurement of several cytokines at multiple time points can be of importance (3). Combining pro- and antiinflammatory cytokines in a single assay yields an overall view on the patient’s inflammatory status; may allow differentiation among infection, sepsis, and enterocolitis; and thus may improve diagnostic accuracy. In neonates, however, particularly preterm neonates, such combined measurements are often hampered by lack of sufficient obtainable blood (1). Furthermore, although the ELISAs are adequate for measuring these cytokines, they often require multiple dilutions to cover a wide concentration range because …