Managing iron deficiency anemia

Is iron deficiency anemia on your differential diagnosis list for all patients with unexplained microcytic anemia? Find out why it should be, how to diagnose the cause of this anemia, and how to treat these iron-deficient patients.

In healthy animals, 98% of oxygen is carried by hemoglobin, with the remainder dissolved in blood. It is the four iron atoms within each molecule of hemoglobin that permit its remarkable oxygen-carrying capacity. Without adequate hemoglobin, oxygen delivery is profoundly compromised.1,2

Anemia, defined simply as a decrease in circulating erythrocyte mass, may be due to several different processes. These may be broadly classified by etiology into a) blood loss, b) hemolysis, or c) ineffective erythropoiesis. Iron deficiency anemia (IDA) bridges two of these categories, as it is a classic cause of ineffective erythropoiesis but is usually due to chronic blood loss.


The clinical signs of IDA are related to decreased red blood cell (RBC) mass and oxygen-carrying capacity. The onset may be insidious, with progressive lethargy, fatigue, and exercise intolerance. On physical examination, mucous membranes will be variably pale. Patients may have a high resting heart rate and tachypnea, with a low-grade systolic heart murmur.

Unusual food cravings, or pica, may be reported. Both dogs and cats may eat soil or rocks; indoor cats may ingest litter. This behavior often resolves when iron stores are replenished.


The hallmark of IDA is microcytic hypochromic anemia, which is indicated by a low mean corpuscular volume and a low mean corpuscular hemoglobin or hemoglobin concentration.1,2 The RBC distribution width is often increased and simply reflects substantial variation in erythrocyte sizes; it may be reported by a technologist as anisocytosis.

Microcytosis is an otherwise uncommon finding, and IDA should be considered in every patient with microcytic anemia. Small RBCs, without anemia, are sometimes noted in Akitas and other Japanese dog breeds. That is normal for these dogs and does not need to be investigated. The other well-recognized cause of microcytosis, with or without anemia, is portosystemic shunting.3-6 The reason for this is unclear. It appears to reflect abnormal iron metabolism but is not associated with true iron deficiency.

It is a common misconception that IDA is a nonregenerative process. In fact, reticulocyte production is variable and may be fairly robust. Iron deficiency should not be discounted just because the absolute reticulocyte count is > 60,000/μl.2

Many IDA patients have increased platelet numbers. The cause of this thrombocytosis is unknown. Thrombocytopenia has been occasionally reported in dogs with IDA.