Poikilocytosis is variation in the shapes of red blood cells.

Normal red blood cells are round, flattened disks that are thinner in the middle than at the edges.

[1] Generally, poikilocytosis can refer to an increase in abnormal red blood cells of any shape, where they make up 10% or more of the total population of red blood cells.

Poikilocytosis may be diagnosed with a test called a blood smear.

[citation needed] The term derives from poikilos (ποικίλος), which means "varied" in Greek.