MEASUREMENT OF RED-CELL DEFORMABILITY IN PLASMA COMPARED WITH BUFFER AS SUSPENDING MEDIUM

Measurements of red cell deformability are usually performed in isoton ic buffer solutions as suspending medium. However, in vivo, red cells are surrounded by plasma in which plasma proteins are present. In this study we investigated whether using plasma (anticoagulated with 1/10 vol. 110 mM trisodium citrate) instead of buffer (phosphate buffered s aline solution) as the suspending medium gives rise to differences in the measured red cell deformability parameters. We used ektacytometry, the micropipette, the flow channel (both static and dynamic), and a C ell Transit Analyzer to study this effect. Where necessary, we added 1 g/l bovine serum albumin to prevent echinocyte formation, and poly-vi nyl-pyrrolidone to increase the buffer viscosity to match that of plas ma. Plasma was found to be a good alternative for buffer as suspending medium except for ektacytometric measurements. In ektacytometry, inte ractions between plasma components and the polymer added to increase t he medium viscosity caused measurement artefacts. Comparison between t he plasma and the buffer measurements using the other techniques showe d a decreased red cell deformability in plasma. We found that in plasm a membrane elasticity is decreased and membrane viscosity is increased compared with buffer (from micropipette and flow channel measurements ) and a decreased filterability in plasma with the Cell Transit Analyz er. It is unclear whether the plasma composition or the buffer composi tion is responsible for the observed increased membrane viscosity and decreased membrane elasticity in plasma or, in other words, the decrea sed viscosity and increased elasticity in buffer. However, our results raise the question whether buffer is a good medium and whether deform ability studies in general should be performed in plasma instead of in buffer.