Even patients with mild COVID‐19 symptoms after SARS‐CoV‐2 infection show prolonged altered red blood cell morphology and rheological parameters

Infection with the novel severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) and the associated coronavirus disease‐19 (COVID‐19) might affect red blood cells (RBC); possibly altering oxygen supply. However, investigations of cell morphology and RBC rheological parameters during a mild disease course are lacking and thus, the aim of the study. Fifty individuals with mild COVID‐19 disease process were tested after the acute phase of SARS‐CoV‐2 infection (37males/13 females), and the data were compared to n = 42 healthy controls (30 males/12 females). Analysis of venous blood samples, taken at rest, revealed a higher percentage of permanently elongated RBC and membrane extensions in COVID‐19 patients. Haematological parameters and haemoglobin concentration, MCH and MCV in particular, were highly altered in COVID‐19. RBC deformability and deformability under an osmotic gradient were significantly reduced in COVID‐19 patients. Higher RBC‐NOS activation was not capable to at least in part counteract these reductions. Impaired RBC deformability might also be related to morphological changes and/or increased oxidative state. RBC aggregation index remained unaffected. However, higher shear rates were necessary to balance the aggregation‐disaggregation in COVID‐19 patients which might be, among others, related to morphological changes. The data suggest prolonged modifications of the RBC system even during a mild COVID‐19 disease course.