The association between C-reactive protein (CRP) and procalcitonin (PCT) levels and the severity of infection in patients with impaired renal function. The differences in CRP and PCT among four subgroups were analyzed using the Kruskal-Wallis test. (a) CRP increased depending on the infection severity (P <0.001). However, there was no difference in CRP between severe sepsis and septic shock (P = 0.549). The median (IQR) CRP in each subgroup was as follows: 3.74 (7.27) when there was no systemic inflammatory response syndrome (SIRS), 10.41 (18.82) in sepsis, 18.59 (15.43) in severe sepsis, and 19.26 (21.94) in septic shock. (b) PCT increased depending on the infection severity (P <0.001). However, PCT was not significantly higher in patients with sepsis than in those without SIRS (P = 0.851). The median (IQR) PCT in each subgroup was as follows: 1.52 (10.78) in the absence of SIRS, 2.22 (5.51) in sepsis, 7.96 (34.97) in severe sepsis, and 25.41 (85.11) in septic shock.