[Adhesions and interference images of unfixed erythrocytes]

For the analysis of deformability in microcirculatory investigations an exact understanding of red blood cell (RBC) geometry is required. To extend knowledge we introduce a new morphological feature of resting unfixed erythrocytes by means of an inverted reflection contrast microscope (RCM). By assessing the interference patterns caused by RCM erythrocytes can be classified according to the depth of their central concavity which depends on the flexibility of the RBC. Moreover, the RBC adhesion can be directly observed. We found out that: 1. Five types of normocytes can be distinguished in RCM. 2. In phase contrast the size distribution of RBC without central concavity (type 5, 11.53% of all normocytes) shows peaks at 48 microns2 and 52 microns2. 3. Image analysis reveals two size categories of relative adhesion areas. One category consists of type 1 and 2 (relative adhesion area 25.63%), the other of the types 3 to 5 (relative adhesion area 39.91%). Besides, RCM allows the reliable identification of pathologic erythrocytes in unstained specimens.