Understanding Why Vets Do Blood Work on Pets

“We’ll need to get some blood work done on your pet,” your friendly vet tells you. You may feel reassured that checks will take place but unsure about why they need to happen at all.

So, what are vets looking for when they carry out blood tests on your pet? Read on to find out. 

Blood Count and Chemical Analysis

Whether it happens before surgery or otherwise, blood work typically involves 2 things:

  • A complete blood count (CBC)
  • A blood chemical analysis 

Blood work acts as an evaluation tool to check on and diagnose certain conditions. Pets, especially those in their senior years, should ideally have blood work as part of their annual examination at the vet. 

When vets draw blood from your pet, they’ll be able to examine both its cells and the fluid the cells travel through.

What Happens During a CBC

The CBC detects the number of:

  • Red blood cells (erythrocytes)
  • White blood cells (leukocytes)
  • Platelets (thrombocytes) or clotting proteins
  • The hemoglobin level
  • The packed cell volume (PCV) or hematocrit

Red blood cells are responsible for carrying oxygen through the body. White blood cells are there to combat infections and form part of the body’s immune system. There are five different kinds of white blood cells: 

  • Eosinophils, lymphocytes, neutrophils, basophils and monocytes 

Platelets are part of your animal’s ability to clot their blood – an obviously important function. When clotting is too slow, it can be a serious issue. 

A CBC can provide your vet with a range of data. This includes information about:

  • The number of red blood cells (the most critical blood cell) and various measurements that give information about their health
  • Your pet’s blood clotting capacity
  • The number of white blood cells and various informative measurements about their appearance

A CBC is useful information for a vast range of disease processes, and is vital for dogs that display symptoms such as:

  • Loss of appetite, pale gums, fever, vomiting, diarrhea or general weakness 

A CBC can also detect bleeding irregularities and other disorders or diseases that would be otherwise difficult to diagnose. Here’s a brief list of some of these: 

  • Anemia
  • Your dog’s hydration levels
  • Autoimmune diseases such as autoimmune hemolytic anemia
  • Blood cancers including some particular lymphomas
  • Tick-borne diseases such as Lyme or Ehrlichia 
  • Certain bacterial infections
  • Viral infections like Parvo or Panleukopenia
  • Bone marrow diseases 
  • Parasitic diseases such as haemobartonella in cats
  • Poisoning from Tylenol or onion toxicity, for example
  • Eosinophils as indicators of parasitic or allergic conditions
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What Happens During Blood Chemistry

A blood chemistry screen typically tests kidney and liver function as well as electrolyte levels. Your vet will run blood chemistries on the fluid found in the blood sample. Specific key tests include those for:

1. Alkaline Phosphatase (ALKP)

Elevated alkaline phosphatase levels are the most typical biochemical irregularities. We can see these in what we’d describe as otherwise healthy animals. Elevated levels can be an indication of: 

  • Liver and bone injury
  • Dental disease
  • Skeletal growth
  • Pregnancy
  • Reactive hepatopathies
  • Animals who’ve been taking glucocorticoids

Growing animals typically have higher levels of this enzyme. Elevated levels can be a tumor marker, especially with those that have metastasized to the liver. Unlike in humans, low levels of alkaline phosphatase may not be clinically significant.

2. Alanine Transaminase (ALT)

Decreased ALT when combined with increased cholesterol levels can be a sign of a congested liver. Decreased ALT may also be a sign of abnormally low general liver function. Increased levels may also indicate liver damage, a kidney infection, chemical pollutants, or myocardial infarction.

3. Bilirubin

You expect elevated levels when there are any of the following: 

  • Liver disease
  • Toxicity due to specific drugs
  • Hemolytic anemia

Decreased levels are indicators of an inefficient liver, excessive fat digestion, and possibly a diet low in nitrogen-bearing foods.

4. Blood Urea Nitrogen (BUN)

Low fluid intake, too much protein, kidney damage, certain drugs, intestinal bleeding, or heart failure can all cause an increase in BUN. Decreased levels can happen because of low nitrogen intake, an unhealthy diet, malabsorption or damage to the liver.

5. Creatinine (CREA)

Low levels can indicate pregnancy, kidney damage or liver disease. Elevated levels can be a sign of kidney disease because it’s the kidney’s job to excrete excess creatinine into the urine. They can also be an indication that certain drugs are impacting kidney function. Increased CREA levels may also be due to muscle degeneration.

6. Glucose (GLU)

You would expect to find elevated levels when a pet is suffering from:

  • Diabetes, liver disease, obesity or pancreatitis because of steroid medications
  • Excessive stress 

Low levels may indicate liver disease, overproduction of insulin, or hypothyroidism.

7. Total Protein (TP)

Decreased levels could be because your pet suffers from:  

  • Poor nutrition
  • Liver disease
  • Malabsorption
  • Diarrhea
  • Severe burns

Your vet would see increased levels in cases of lupus, liver disease and chronic infections.

8. Albumin (ALB)

High levels are rare and typically due to dehydration. Low levels indicate liver disease, poor diets, diarrhea, fever, infection, insufficient iron intake and serious burns.

9. A Range of Other Tests

Your vet may also be looking to drill further into the chemical make-up within the blood. This could include taking a look at calcium levels. Changes from normal levels can indicate a variety of diseases. These include: 

  • Tumors and kidney disease
  • Hyperparathyroidism

Cholesterol levels can act as an aid to diagnose hypothyroidism, liver disease, Cushing’s disease and diabetes mellitus.

Low levels of the thyroid hormone, Thyroxine, can indicate hypothyroidism in dogs – while the converse is true for hyperthyroidism in cats.

Finally, looking at other electrolytes such as sodium and potassium can give additional diagnostic information in assessing the health of your pet.

Book Your Pet’s Annual Check-up Now

There’s a lot a vet can find out about your pet by taking a sample of blood. Some diseases are preventable and so catching the early signs can make for a far better prognosis. That’s why it is so important to get your pet checked regularly by a vet.

Do you still have any questions about the blood work your pet should have? Then schedule a video consultation with one of our qualified vets! We have a team of qualified vets on hand to give you reassurance and advice. We also have a range of highly competitive pet insurance products available too. 

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