Severity of neutropenia relates to the relative risk of infection and is classified as follows: Mild: 1000 to 1500 / mcL (1 to 1.5 × 10 9 / L) Moderate: 500 to 1000 / mcL (0.5 to 1 × 10 9 / L) Severe: < 500 / mcL (< 0.5 × 10 9 / L) When neutrophil counts fall to < 500 / mcL, endogenous microbial flora (eg, in the mouth or gut) can cause infections.