Deformability can in effect be measured indirectly, such as by how much pressure and/or time it takes cells pass through pores of a filter (i.e., filterability or filtration)[10] or perfuse through capillaries (perfusion),[11] in vitro or in vivo, having smaller diameters than the cells'. Some deformability tests may be more physiologically-relevant than others for given applications. For example, perfusion is more sensitive to relatively small changes in deformability (compared to filterability),[12] thus making it preferable for assessing RBC deformability in contexts where microcirculatory implications are of particular interest.