Anaemia in Pets
Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS
Table of Contents
Anaemia refers to an abnormally low number of red blood cells in the circulation. It is a symptom of many different conditions rather than a diagnosis, however, anaemia can often be the first sign identified clinically or on a blood test.
Red blood cells are made in the bone marrow, before being released in to the circulation in their immature form. It takes roughly 48 hours for these to mature into red blood cells. Broadly speaking, anaemia happens when insufficient red blood cells are being produced, red blood cells are being used faster than they can be replaced, or red blood cells are being destroyed.
Anaemia can be divided into two categories;
- Regenerative anaemia – where the body is trying to correct the problem
- Non-regenerative anaemia – where the body is not compensating for the anaemia
Red blood cells are responsible for carrying oxygen around the body. When there are not enough red cells, pets become lethargic and may struggle to exercise, or be less interested in food. Strangely, sometimes pets may start licking or eating non-food items, known as pica. On clinical examination, the mucous membranes (inside the lips and eyelids) are often very pale pink, white or yellow (due to jaundice). Patients may have other symptoms caused by the underlying cause of the anaemia.
Anaemia can develop slowly, over several weeks or months, or very rapidly. In slow cases, the symptoms may not be as severe as the animal has time to adjust to the anaemia. In rapidly progressing cases, the sudden reduction in red blood cells can cause collapse and jaundice.
The first step in diagnosis of anaemia is a blood test including haematology and biochemistry. This will include a red blood cell count to confirm the presence and severity of anaemia. It will also screen for other relevant changes, such as platelet and white blood cell count, and provide an overview of organ function. Often, if anaemia is present, it is recommended to send a blood smear to an external lab for review by a specialist pathologist. This will allow assessment of the red blood cells and determine if the anaemia is regenerative or not.
Anaemia is measured by looking at the packed cell volume (PCV), which tells us what percentage of the blood is red blood cells. A normal PCV for a dog is 35-50%. If new red blood cells are being produced, or red cell loss is ongoing, PCV can change rapidly.
There are many causes of anaemia, and more specific tests will be required to find the root problem. Each test we perform guides our next steps. Due to the number of possible causes, sometimes many tests must be performed to reach a final diagnosis. This can take time, however, it is important that we follow a logical approach so that we do not miss something important. Each case is different, but common investigations include further blood tests, imaging (such as x-ray, ultrasound or CT), and sometimes more invasive testing such as endoscopy or bone marrow biopsy.
When planning diagnostic testing, your vet must consider many different causes of anaemia.
1. Insufficient red blood cells are being produced
Red blood cells survive only for a few weeks, so new cells must be made continuously. Conditions such as kidney failure or some endocrine (hormonal) diseases can block this process, causing anaemia. This is also seen with dietary deficiencies, including iron, copper and some B vitamins, or lead poisoning. Primary conditions of the bone marrow will also lead to lack of red cell production, such as some viruses, toxins or cancers.
2. Red blood cells are being used faster than they can be replaced
This generally happens due to blood loss, which occur suddenly or be more long-standing. Blood loss can occur internally or externally. External bleeding (such as nose bleeds or bleeding from wounds) can be more obvious than internal bleeding (such as bleeding into the abdomen, blood in the urine, or minor bleeds within the gastrointestinal tract). Generally, chronic bleeding is of a low volume and will be more challenging to see any symptoms. Blood loss can occur due to many reasons, for example trauma, infections, tumours, bleeding disorders, or gastrointestinal ulcers.
3. Red blood cells are being destroyed
The body sometimes destroys its own red blood cells. This most often happens due to a malfunction of the body’s immune system (known as immune-mediated haemolytic anaemia, or IMHA), but can also occur due to toxins, genetic defects, or internal damage to the red blood cells. IMHA can be primary, with no underlying cause, or secondary to another condition, such as a drug reaction, infection, or cancer elsewhere in the body.
Treatment of anaemia depends very much on the underlying cause. Depending on the severity of illness, patients with anaemia may be managed at home, or may need to be hospitalised. Patients who are bright, eating and drinking may be able to remain at home while we wait for test results, but will often need to return for further investigations. Patients who are lethargic, not eating or severely anaemic may require hospitalisation for investigations, supportive care and close monitoring. While we wait for a diagnosis, additional medications may be given to help manage symptoms, such as anti-nausea drugs, gastro-protectants and fluids.
Red blood cells can be administered via a blood transfusion. This can be obtained from a donor dog, or ordered from the pet blood bank. Blood transfusions carry a small risk of allergic reaction but this is rare. More common, is the possibility that the immune system will destroy the new cells, meaning for some patients, blood transfusions only lead to short-term improvement. The need for a blood transfusion is determined by the degree of anaemia present, how the dog is coping clinically, and the likely cause of the anaemia.
It is impossible to give a single prognosis for pets with anaemia, due to the wide variety of possible causes. Some conditions are very responsive to treatment, while others cannot be cured but may be managed for some time. Unfortunately, anaemia caused by cancer often carries a guarded prognosis, especially if the bone marrow is directly affected.
The best prognosis comes from an accurate diagnosis, so it is essential to be patient until the root cause is found. At this point, your vet will be able to explain the treatment options available, and the likely prognosis.
Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.
Page last reviewed: 16th January 2024
Next review due: 16th January 2026