Automated bedside flow cytometer for mHLA-DR expression measurement: a comparison study with reference protocol

Mehdi Zouiouich, Morgane Gossez, Fabienne Venet, Thomas Rimmelé, Guillaume Monneret

In various ICU conditions, measurement of diminished expression of human leukocyte antigen-DR on circulating monocytes (mHLA-DR) by flow cytometry appears to be a reliable marker of acquired immunosuppression. Low mHLA-DR is associated with an increased risk of nosocomial infections and mortality. Nevertheless, its use remains somewhat limited and has not been adopted in common medical practice. The main drawback of mHLA-DR measurement is likely related to the use of flow cytometry that is not accessible everywhere on a 24/7 basis. Recently, the Accellix system, a fully automated table top cytometer, was developed for use at bedside or emergency labs. The objective was to assess the performance of the Accellix (beta site evaluation including repeatability and method comparison with reference protocol) for the measurement of mHLA-DR expression. Accellix repeatability at low and high expression levels of mHLA-DR was < 10% (i.e., within the range of acceptability for clinical flow cytometry). In comparison study including 139 blood samples (67 septic shock patients and 17 healthy volunteers), Pearson's correlation parameters (r (2)) ranged from 0.71 to 0.97 (p < 0.001). Intra-class correlation coefficient was 0.92. This fully automated table top cytometer appears to be a suitable tool for ICU patient monitoring and on-going clinical trials as there is no sample preparation and no need for specific skills in flow cytometry. Upon validation in a larger cohort study to reinforce reliability, Accellix could represent a major step to make flow cytometry accessible to clinicians by placing the instrument inside intensive care units or emergency laboratories.