Effects of plasma donation on blood rheology and peripheral vascular function.

Plasma donation, the removal of plasma and reinfusion of cellular components, is widely used to produce plasma-derived products; however its physiological effects on blood rheology and peripheral vascular function remain poorly understood. This study investigated the effects of plasma donation (Investigation 1) on blood viscosity, red blood cell (RBC) deformability and aggregation, and brachial artery reactive hyperaemia flow-mediated dilatation (RH-FMD), and compared these responses with those induced by frusemide-mediated haemoconcentration (40 mg; Investigation 2) to isolate the independent effects of plasma volume contraction. In Investigation 1, 15 participants (7 females; 25 ± 5 years) underwent plasma donation and were assessed at baseline, immediately after, and 24 h following donation. In Investigation 2, 13 participants (6 females; 24 ± 5 years) underwent diuresis (i.e. plasma contraction), with measurements taken pre- and 4 h following frusemide. Blood rheology parameters and RH-FMD were evaluated at each time point. Both interventions similarly increased haemoglobin (∼8%) and whole blood viscosity (7.6% post-donation; 13.1% post-diuresis, P<0.001), but neither altered shear stress, blood flow, or vascular reactivity. Plasma donation, but not plasma contraction, acutely reduced RBC deformability (theoretical maximum elongation index, P = 0.0403) and increased reactive hyperaemia (∼23%, P = 0.0386), with RBC deformability recovering (P = 0.589) and aggregation decreasing by 24 h (P = 0.0107). Systolic blood pressure declined following plasma donation (P = 0.0123) and remained reduced at 24 h (P = 0.0457), which was not observed following plasma contraction. These findings suggest that plasma donation transiently impairs RBC deformability, lowers systolic pressure, and enhances microvascular reactivity. These effects are unlikely driven by haemoconcentration and may instead reflect changes in macromolecules, RBC mechanics, or anticoagulants. KEY POINTS: Plasma donation is becoming increasingly common due to the global demand for plasma-derived therapeutics. Despite its widespread use, the consequences of plasma donation for blood rheology (e.g. red blood cell deformability) and vascular health remain poorly understood. In this study, we compared individuals who underwent plasma donation with those who ingested an oral diuretic, which reduced plasma volume through diuresis, to isolate the effects of haemoconcentration. Neither intervention altered most blood rheology or vascular function. However, plasma donation transiently reduced red blood cell deformability and enhanced microvascular function. These findings indicate that plasma donation does not adversely affect blood rheology or vascular function and may promote transient beneficial vascular effects, suggesting minimal impact on blood rheology and vascular function.