Red blood cell crenation. Coloured scanning electron micrograph (SEM) of two red blood cells (erythrocytes). The cell on the bottom is normal. The cell on the top is crenated (spiked) and is termed an echinocyte. This occurs due to osmosis when a blood sample is exposed to a concentrated solution. It may be symptomatic of uraemia (accumulation of nitrogenous waste in the blood) but more usually is the result of prolonged storage of a blood specimen. Erythrocytes contain the red pigment haemoglobin, allowing them to transport and supply oxygen. Magnification x3250 at 6x7cm size.