Anemia
A reduction in the number of red blood cells or hemoglobin concentration in the blood, resulting in decreased oxygen-carrying capacity. Anemia is a clinical finding, not a diagnosis — it always indicates an underlying condition requiring investigation.
Anemia is defined by a reduction in red blood cell (RBC) mass, measured by hematocrit (packed cell volume, PCV) or hemoglobin concentration. Normal canine hematocrit ranges from approximately 37-55%. Values below 37% indicate anemia, though clinical significance depends on severity and rate of onset.
Types of Anemia
Anemia is classified by mechanism and red blood cell characteristics:
By Mechanism
- Regenerative anemia: the bone marrow is actively producing new red blood cells (reticulocytes) in response to the anemia. This indicates blood loss or red blood cell destruction as the cause. A reticulocyte count above 60,000/mcL suggests regeneration.
- Non-regenerative anemia: the bone marrow is not producing adequate new red blood cells. This points to bone marrow disease, chronic disease, iron deficiency, or renal insufficiency.
By Cause
- Blood loss anemia: external or internal hemorrhage. Causes include trauma, GI bleeding, coagulation disorders, ruptured tumors (hemangiosarcoma), and surgical blood loss.
- Hemolytic anemia: red blood cells are being destroyed faster than they can be replaced. Causes include immune-mediated hemolytic anemia (IMHA), toxin exposure (zinc, onion, garlic), infectious agents (Babesia, Mycoplasma), and oxidative damage.
- Anemia of chronic disease: reduced red blood cell production associated with chronic inflammation, infection, cancer, or kidney disease. The body sequesters iron as part of the inflammatory response, limiting its availability for erythropoiesis.
- Aplastic or hypoplastic anemia: bone marrow failure from drugs, toxins, infectious agents, or immune-mediated destruction of marrow precursors.
Clinical Signs
The signs of anemia reflect reduced oxygen delivery to tissues:
- lethargy and exercise intolerance
- pale mucous membranes (gums, conjunctiva)
- increased heart rate and respiratory rate (compensatory)
- weakness and collapse in severe cases
- jaundice (if hemolysis is the cause)
Diagnostic Approach
A complete blood count (CBC) is the starting point. Reticulocyte count, blood smear examination, serum chemistry, and additional targeted tests (Coombs test for IMHA, abdominal imaging for internal bleeding, bone marrow biopsy for non-regenerative cases) guide identification of the underlying cause.
Anemia is never the final diagnosis — it is always a signal pointing to something else. The clinical priority is identifying and treating the cause, not just addressing the low red blood cell count.