An improved filtration rate for measuring red cell deformability.

In order to follow the filtration of a red cell suspension with time, the filtration technique described (1) has been modified. The red cell suspension is filtered through a polycarbonate membrane filter (pore diameter 5 micron) under gravitational force. The filtrate is collected in a plastic tube connected to an isometric transducer, the output of which is registered on a chart recorder. The linear part of the curve obtained is used to calculate the slope and the relative filterability (RF) ie the ratio of the rate of flow of the red cell suspension to the rate of flow of the suspending medium. The reproducibility of the technique is demonstrated by a less than 5% coefficient of variation in one blood sample less than 5% interobserver variation and a weekly variation from the same donor of less than 5%. The fast filtration rate of a highly diluted red cell suspension (0.5-1%) may be followed with this technique, taking the first 15 seconds to calculate it. The technique has proved useful in detecting differences in red cell deformability in connective tissue disorders (Scleroderma, Raynaud's phenomenon) also between stored and freshly prepared red cell suspension and its improvement by drugs (pentoxifylline, dipyridamole).