Can a Complete Blood Count Show Anemia in Horses?

Sometimes results on a complete blood count (CBC) are mistakenly used to diagnose iron deficiency. While some changes in the CBC can point toward iron deficiency, it actually gives information about the red blood cells and their hemoglobin content. Adequate body stores of iron are essential to produce red blood cells, but many other nutrients including B vitamins, copper, and protein are also required. This article summarizes some of the information found on a CBC report.

Hemoglobin (Hb) is the pigment in red blood cells that contains iron and allows them to transport oxygen.

Hematocrit (Hct) or packed cell volume (PCV) tells the percent or volume of red blood cells that are present in blood when it is centrifuged. The remainder of the blood is its liquid portion, the plasma.

Red blood cell or erythrocyte count (RBC) tells the number of red blood cells in one microliter (1/1,000,000th of one liter) of blood.

Mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) are different ways of expressing the concentration of hemoglobin relative to either the hematocrit or number of red blood cells in the blood.

Iron deficiency and iron deficiency anemia are very rare in horses, especially in those allowed to graze. In fact, if horses have access to pasture and turnout, iron deficiency is unlikely.

Anemia can be caused by a wide variety of illnesses, drugs, and other nutrient deficiencies. Measurement of blood transferrin, an iron transport and storage protein, is more reliable to diagnose iron deficiency.

The most common cause of anemia is called anemia of inflammation, which is a normal response of the body to chronic inflammation or infection. The body will sequester its iron stores at its own expense to help fight infection because bacteria also require iron for their metabolism and growth. Other common causes of anemia are chronic blood loss (gastric or colonic ulcers) and parasitism.

Consult with your veterinarian whenever you suspect signs of anemia in your horse. Routine laboratory tests can quickly and economically rule out many common causes of anemia.