An in vitro method for diagnosing and treating sepsis in a patient is provided, the method including: contacting at least a portion of a biological sample from the patient consisting essentially of microparticles isolated via differential centrifugation with reagents for detection and/or quantification of neutrophil-derived microparticles; determining a level of neutrophil-derived microparticles based on the contacting step; diagnosing sepsis in the patient when the determined level of neutrophil-derived microparticles is elevated relative to a cutoff value of the neutrophil-derived microparticles; and treating the diagnosed patient for sepsis.