Monocyte subset distribution is associated with mortality in critically ill patients.

Although patients admitted to an intensive care unit (ICU) suffer from various pathologies, many develop a systemic inflammatory response syndrome (SIRS). As key regulators of innate immunity, monocytes may be crucially involved in SIRS development. Monocytes can be distinguished into three subsets: Classical monocytes (CD14++CD16-; CM), non-classical monocytes (CD14+CD16++CCR2-; NCM) and intermediate monocytes (CD14++CD16+CCR2+; IM). The aim of this prospective, observational study was to analyse whether monocyte subset distribution is associated with 30-day survival in critically ill patients. A total of 195 consecutive patients admitted to a cardiac ICU at a tertiary-care centre were enrolled, blood was taken at admission and after 72 hours and monocyte subset distribution was analysed. Mean APACHE II score was 19.5 ± 8.1 and 30-day mortality was 25.4 %. At admission, NCM were significantly lower in non-survivors as compared to survivors [2.7 (0.4-5.5) vs 4.2 (1.6-7.5)%; p=0.012] whereas CM and IM did not differ according to 30-day survival. In contrast, 72 hours after admission, monocyte subset distribution shifted towards an increased proportion of IM [8.2 (3.9-13.2) vs 4.2 (2.3-7.9)%; p=0.003] with a concomitant decrease of CM [86.9 (78.6-89.2) vs 89.6 (84.9-93.1)%; p=0.02] in non-survivors vs survivors, respectively. NCM at day 3 were not associated with death at 30 days. These results were independent from age, gender, CRP, APACHE II score and primary diagnosis. In conclusion, circulating monocyte subsets are associated with 30-day mortality in critically ill patients. The innate immune system as reflected by monocyte subset distribution may play a major role in ICU outcome despite varying admittance pathologies.