Red blood cells carry vital oxygen around the body. A shortage of red blood cells in the circulation is called anaemia. There are many different causes of anaemia in dogs and in most cases a variety of tests will be needed to diagnose the underlying problem. Severe anaemia can be life-threatening and requires urgent treatment.
Red blood cells are important cells that transport oxygen around the body. Red blood cells are mainly made in the bone marrow and also, to some extent, in the liver and spleen. They (and therefore blood) are coloured red because they contain a pigment called haemoglobin.
The red blood cells pick up oxygen whilst travelling through the lungs and transport this to the body tissues, where it is exchanged for the waste gas carbon dioxide. The red blood cells transport the carbon dioxide back to the lungs where it is removed from the body in exhaled breath.
Red blood cells are active for around 115 days, at which point they are removed from the circulation. Continuous normal production by the bone marrow ensures that the total numbers remain the same.
In the early stages, there may be few symptoms of anaemia. This is especially the case if anaemia develops very gradually because the body tends to adapt to the anaemia. The first sign of anaemia may be low energy levels and general weakness due to reduced oxygen supply to the muscles. Anaemic animals often have a poor appetite. In severe cases more dramatic signs may be seen such as collapse and rapid breathing. If you lift your dogs lips you may notice that its gums are pale or even white.
Your vet will be able to examine your dog more closely to identify the signs of anaemia. Depending on what is causing the anaemia, there may also be other changes such as jaundice or a swollen belly. Making the diagnosis of anaemia is usually relatively straightforward, however your vet may need to perform a number of tests to find out what is causing the anaemia. It is important to establish the cause of anaemia in order to treat the underlying condition.
Common tests that may be required include:
- Blood tests: these allow an assessment of the severity of the anaemia, and also in some cases indicate why it is occurring. A large number and variety of tests may be required; tests are often repeated frequently to assess progress and response to treatment.
- X-rays and ultrasound scans: these may be used to look for internal problems causing the anaemia, eg blood loss into the abdomen or chest, or perhaps cancers.
- Biopsies: especially of the bone marrow, to assess its function and to look for abnormalities. Tumours may also be biopsied to help in planning treatment.
Anaemia can develop in a number of ways. The simplest is severe blood loss from the body, e.g. after an accident. This process is called haemorrhage and arises when arteries or veins are damaged, allowing blood to escape from the circulation. First aid in accident and emergency situations is designed to limit blood loss as much as possible.
Haemorrhage can also occur much more slowly if small amounts of blood are lost from the body over a prolonged period of time. This type of bleeding is often associated with cancers which bleed within the body. If blood loss is occurring slowly, particularly if bleeding is into the urine or faeces it is sometimes not noticed until signs of anaemia develop. In these cases the anaemia may be quite severe before signs are noticed because the body has time to get used to the lower oxygen levels.
There are many other causes of anaemia which are seen regularly in dogs. The anaemia generally arises because either there is a problem with red blood cell production or the cells are being destroyed in larger numbers than normal. If the bone marrow cannot produce red blood cells at the same rate as they are being lost then replacement of old cells does not occur and anaemia eventually develops.
If the bone marrow is working properly red cell production will be stepped up if the animal becomes anaemic. As the cells are produced and released more quickly from the marrow young red cells appear in the blood. These cells can be detected on a blood test and indicate that the bone marrow is responding to the problem. If the bone marrow is not functioning normally new cells are not produced.
One of the challenges for the veterinary surgeon is to determine exactly why the anaemia is occurring, and how the body is responding. It is important to investigate all anaemias so that the correct treatment can be worked out.
Effective treatment depends on the diagnosis of the underlying problem. Surgical or medical options may be available depending on the cause. If the immune system is destroying red blood cells within the body then drugs can be given to modify the actions of the immune system. Certain blood parasites may cause anaemia and these can be treated with appropriate medication. Surgery may be needed, for example to remove a bleeding cancer in the spleen.