Illustration of an abnormal red blood cell (erythrocyte) known as a burr cell, or echinocyte. Red blood cells with this appearance (many small, evenly spaced thorny projections) can occur as an artifact of staining or drying blood samples. They are also found in association with conditions such as uraemia, (urea in the blood), metabolic disorders such as pyruvate kinase deficiency, liver dysfunction, low blood levels of magnesium or phosphate, and haemolytic anaemia in long-distance runners.