Circulating immunoglobulin M (IgM) at various stages of severity. IgM levels were measured in serum within the first 24 hours from diagnosis of systemic inflammatory response syndrome (SIRS) (n= 41), of sepsis (n= 100), of severe sepsis (n= 113) and of septic shock (n= 78). Serum IgM levels for healthy volunteers (n= 35) are also provided. Circles denote outliers. P values of comparisons with patients with septic shock after Mann-Whitney U test and correction for multiple comparisons are provided.