Despite the ongoing development of automated hematology analyzers to optimize complete blood count results, platelet count still suffers from pre-analytical or analytical pitfalls, including EDTA-induced pseudothrombocytopenia. Although most of these interferences are widely known, laboratory practices remain highly heterogeneous. In order to harmonize and standardize cellular hematology practices, the French-speaking Cellular Hematology Group (GFHC) wants to focus on interferences that could affect the platelet count and to detail the verification steps with minimal recommendations, taking into account the different technologies employed nowadays. The conclusions of the GFHC presented here met with a "strong professional agreement" and are explained with their rationale to define the course of actions, in case thrombocytopenia or thrombocytosis is detected. They are proposed as minimum recommendations to be used by each specialist in laboratory medicine who remains free to use more restrictive guidelines based on the patient’s condition.

Summary: COVID‐19 has compelled scientists to better describe its pathophysiology to find new therapeutic approaches. While risk factors, such as older age, obesity, and diabetes mellitus, suggest a central role of endothelial cells (ECs), autopsies have revealed clots in the pulmonary microvasculature that are rich in neutrophils and DNA traps produced by these cells, called neutrophil extracellular traps (NETs.) Submicron extracellular vesicles, called microparticles (MPs), are described in several diseases as being involved in pro‐inflammatory pathways. Therefore, in this study, we analyzed three patient groups: one for which intubation was not necessary, an intubated group, and one group after extubation. In the most severe group, the intubated group, platelet‐derived MPs and endothelial cell (EC)‐derived MPs exhibited increased concentration and size, when compared to uninfected controls. MPs of intubated COVID‐19 patients triggered EC death and overexpression of two adhesion molecules: P‐selectin and vascular cell adhesion molecule‐1 (VCAM‐1). Strikingly, neutrophil adhesion and NET production were increased following incubation with these ECs. Importantly, we also found that preincubation of these COVID‐19 MPs with the phosphatidylserine capping endogenous protein, annexin A5, abolished cytotoxicity, P‐selectin and VCAM‐1 induction, all like increases in neutrophil adhesion and NET release. Taken together, our results reveal that MPs play a key role in COVID‐19 pathophysiology and point to a potential therapeutic: annexin A5.

Mean corpuscular haemoglobin concentration (MCHC) is determined by the ratio of haemoglobin concentration to haematocrit. Managing increased MCHC presents significant challenges, mainly due to variations in analytical methods and pathophysiological conditions. Depending on the haematological analyser (HA), MCHC can be measured directly or calculated. It is important that all people involved in hematocytometry must identify and correct artefacts to ensure accurate erythrocyte parameters. In order to harmonise and standardise haematology practices in all laboratories, the French‐speaking Cellular Haematology Group (GFHC) has reviewed the interferences and pathophysiological situations that could increase MCHC, and the advice on how to manage cases of elevated MCHC. We will review current techniques, such as impedance and optical methods, for accurate determination of MCHC. We will also examine the interferences that can artificially increase MCHC; and the pathophysiological conditions responsible for such increases. Finally, we will present guidelines for the management of elevated MCHC, including strategies to bypass interferences and determine which erythrocyte parameters can be reliably reported, as well as the acceptable MCHC values for various pathophysiological variations.

The British Journal of Haematology publishes original research papers in clinical, laboratory and experimental haematology. The Journal also features annotations, reviews, short reports, images in haematology and Letters to the Editor.