The range of normal values can vary greatly because there are so many different kinds of psittacine birds. There are also differences between juvenile and adult birds. In a healthy bird, most RBCs should be mature but a small percentage of immature erythrocytes is expected, which indicates a normal replenishment from the bone marrow. Immature RBCs are slightly larger than mature RBCs, and the cytoplasm is lightly-stippled which produces a difference in color. If a bird is anemic and shows slight to no polychromasia or anisocytosis over a period of several weeks, this can indicate that the bone marrow is depressed or non-regenerative which is a grave situation.
Anemia means a decrease in the normal amount of red blood cells.
It can be due to either blood loss or lack of production of new RBCs from the bone marrow. This number is expressed as a percentage. It is determined by putting a sample of blood in a tiny collecting vial called a microhematocrit tube. At the laboratory this tube is spun in a centrifuge which separates the red blood cells from the plasma. The normal number of RBCs varies depending on whether the bird is a juvenile or adult and the kind of bird being examined.