Assessment of monocytic HLA-DR expression in ICU patients: analytical issues for multicentric flow cytometry studies

read with interest the recent report by Gogos and colleagues [1]. While the rationale for their study is excellent, we would like to comment on technical issues that may have infl uenced the results. As stated, a time limit of 8 hours between sample drawing and staining at a central laboratory was specifi ed [1]. Unfortunately, information regarding transport conditions is missing (average time, temperature). Th is seems important since monocytic HLA-DR expression (mHLA-DR) increases artifi cially over time [2,3]. Conse quently, recommendations suggest that sample staining for mHLA-DR should occur within 4 hours [2,3]. Although the authors aimed to address the eff ect of transportation, they inappropriately used samples present ing with already near-maximal mHLA-DR values (>90%) before storage. We therefore assume that mHLA-DR results may be falsely elevated due to prolonged transportation times. Furthermore, mHLA-DR modulation during sepsis takes days and consecutive measurements are required [4]. Assessment of one early sample (within the fi rst 24 hours) is probably inappropriate to investigate the impact of infection on mHLA-DR. Similarly, apoptosis staining should not be performed after 8 hours and experts' recommendations highlight the need for dedicated protocols on fresh cells [5]. We are convinced that successful future trials in sepsis will rely on our capacity to accurately assess immune responses. In that sense, fl ow cytometry multicentric clinical studies are essential. Such trials should be performed in standardized environments in accordance with specifi c (pre)analytical requirements. Otherwise, results might be misinterpreted and may impede promising new avenues in future care of septic patients. Abbreviations ICU, intensive care unit; mHLA-DR, monocytic human leukocyte antigen DR-1. Competing interests The authors declare that they have no competing interests. Early alterations of the innate and adaptive immune statuses in sepsis according to the type of underlying infection. A: Analytical requirements for measuring monocytic human lymphocyte antigen DR by fl ow cytometry: application to the monitoring of patients with septic shock. D: Monitoring temporary immunodepression by fl ow cytometric measurement of monocytic HLA-DR expression: a multicenter standardized study. Persisting low monocyte human leukocyte antigen-DR expression predicts mortality in septic shock. Assessment of monocytic HLA-DR expression in ICU patients: analytical issues for multicentric fl ow cytometry studies.