What can blood tests tell vets about the health of your pet?

What can blood tests tell vets about the health of your pet?

Health & Safety

If your pet is sick and ends up in a consultation room, the vet should always ask questions about the pet to take the recent medical history, of what has been happening, any symptoms seen at home, and of course what the problem seems to be. The pet will have a full examination including their temperature being taken, the respiratory rate and their heart rate. The vet will also check over for any signs of pain. Sometimes if the pet has come in for specific symptoms, such as vomiting, the vet may elect to do some blood tests. But what are they actually testing for and what can the results tell them? In this Pets4Homes article, we will look into what blood tests can actually tell vets about different types of diagnosis.

So, what about the main symptom – doesn’t that tell enough?

The main symptom, for example, vomiting, can tell the vet that something is not agreeing with the gastrointestinal system of the animal. The owner may say it is just something the pet has eaten, and while this may be true, it can also be numerous other things causing the vomiting. To emphasise this, and why the vets may need more tests, take a look at just some of the causes of vomiting in dogs.

  • Food allergy.
  • Dehydration.
  • Parasites.
  • Heat stroke.
  • Foreign objects.
  • Viral infection.
  • Bacterial infection.
  • Cancers.
  • Kidney failure.
  • Drug side effects.
  • Liver failure.

And many more as well. So, you can see why sometimes without further tests, it can be extremely difficult to diagnose the actual cause of the vomiting.

So how do blood tests help then?

Well firstly, did you know that blood is actually classed as an organ? And for obvious reasons, it is one of the most important. It has numerous functions, including helping the body to fight infection, helping the body maintain hydration but as a transport organ it does one major job – it carries things around the body including nutrients, waste and of course oxygen.

Because blood visits all the other organs in the body, it also contains chemicals from those organs – even a trace of a chemical can be looked at and will give an indication to how the body’s organs are performing.

So how do vets know which bits to look at?

As you can imagine there are thousands of trace chemicals in the blood, in fact only 1 mL of blood can contain thousands. It would be completely impossible to test them all, so the vet will screen for chemicals that have been highlighted to show how a particular body system is working. In this way, the vet can carefully narrow down the possible causes and concentrate on treating the symptoms or disease, with the best treatment.

So how can you narrow down from thousands of chemicals?

In looking for common problems that can affect your pet and give symptoms such as vomiting, blood tests are normally divided into two parts:

  • Haematology
  • Biochemistry

Haematology – what is it?

Haematology is the study of blood cells and it can tell vets many different things just by the type of cell, number of cells, and shape the cell. Modern techniques mean a machine can examine the blood cells, specifically counting them. Microscopes are also used manually to look at cells for damage and disease.

The most common cell in the body is the red blood cell, also known as an erythrocyte. Red blood cells can tell many things about how the patient is health wise. One of the first tests that are performed on red blood cells is counting them. For example, if the count for them is low, the patient may be showing signs of anaemia or dehydration among other things.

If the red blood cell has a different shape than it should have, it can suggest several types of problem:

  • Feline Infectious Anaemia (FIA) – which is a blood parasite.
  • Immune-Mediated Haemolytic Anaemia (IMHA).
  • Poisoning.
  • Deficiency of iron.

These are just some of the types of problems red blood cells that have changed their shape can point to. For anaemias, they can also indicate whether the condition is regenerative or non-regenerative (that is whether the body can make new red blood cells or not).

Other parts that can interest are the counting of platelets – these are very important in blood clotting, and if these are reduced, the blood may have trouble in clotting.

By far the most indicative factor in haematology can be the white blood cells. The three main types can suggest various problems. An example of these white blood cells are:

  • Neutrophils – a high number of these can indicate an infection, a low number can mean the body is fighting an infection or even the immune system is compromised.
  • Lymphocytes – again these can indicate an infection or even leukaemia.
  • Eosinophils – different ratios of these can indicate allergies or parasites.

So, what is biochemistry?

Biochemistry is the actual study of all the chemicals found in the blood. These chemicals can tell vets a great deal of what is going on inside the animal’s body. Usual chemicals found in the blood are salts, nutrients, and waste, but cells that have been compromised can also release other chemicals such as proteins which gives even more of an insight into the animal’s health. When a pet comes in that need a blood test the standard procedure is to test for 12 to 13 important substances in the blood, and analyse any changes from the normal, that may indicate a health problem.

The standard screen often comprises of:

  • Blood glucose – diabetes is an example of a high reading.
  • Blood urea nitrogen – is the main waste product from proteins. A low reading usually means liver disease, whilst a high reading can indicate kidney failure or dehydration among other things.
  • Albumin – this is a transport protein. Dehydration is one symptom of a high reading, whilst a low reading can mean that animal has had severe blood loss.
  • Globulin – basically the other proteins in the animal’s body. Usually, a high reading indicates an infection, cancers or inflammation.
  • Total protein – these are the levels of albumin and globulin proteins together.
  • Creatinine – kidney failure is common with raised levels.
  • Alkaline phosphatase – raised levels can mean liver disease among other health problems.
  • Cholesterol – normally non-specific in animals, although a high reading can indicate fatty liver disease in cats.
  • Alanine aminotransferase – a liver enzyme, with high readings suggesting liver damage
  • Total bilirubin – high readings can indicate jaundice.
  • Sodium – a very important salt in the blood, this level changes with dehydration or salt poisoning.
  • Potassium – another salt in the body, changes in levels can indicate kidney disease, severe vomiting or even necrosis of tissue.
  • Calcium – changes can include cancers, kidney disease or bone disease among other health issues.


The reason for taking blood and having it analysed for trace chemicals should now be clear. Vets stand a much better chance of treating an animal successfully, when they have diagnostic knowledge at their fingertips. So, if your pet needs a blood test, you can now be confident of what they are testing for – of course there are many other tests other than the ones listed above. Depending on the symptoms, it dictates what tests will be carried out.



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