Poikilocytosis

The presence in the blood of erythrocytes showing abnormal variation in "shape". Mnemonic is when compared to Anisocytosis. Both the words "Shape" and "Poikilocytosis" contain a "P". Therefore Poikilocytosis has to do with RBC Shape variation while Anisocytosis (No "P" in the word) has to do with variation of "size" (No "P" in the word).