High blood pressure in cats also known as “hypertension” is a common problem, especially in older cats. But why do our cats get high blood pressure? In cats, high blood pressure is often a result of an underlying illness that disrupts the body’s regulatory systems responsible for maintaining normal blood pressure. This is termed “secondary hypertension”. This differs from the condition in humans in which it is more common to have raised blood pressure as a primary problem without another cause. 

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The most common underlying disease process that causes high blood pressure in cats is kidney disease. Hyperthyroidism is also strongly connected to higher blood pressure in cats. 

How is blood pressure controlled in the cat’s body?

When a cat’s heart contracts, it pushes blood throughout the body in blood vessels to supply the body with oxygen, energy, and nutrients. Depending on the body’s requirements for energy, whether your cat is sleeping or actively on the move, the heart rate will change to deliver more or less oxygen and energy to the body, lungs, muscles, and organs in order to fulfil their functions. The kidneys, blood vessels and other organs in the body all have a role in detecting and controlling blood pressure in the vessels.

What is high blood pressure? 

High blood pressure, or hypertension, refers to a condition whereby the pressure in blood vessels is unusually high. Without treatment, high blood pressure in cats can lead to serious problems and damage to the body and organs, such as loss of vision, neurological problems, seizures, and heart damage. 

Cat high blood pressure is diagnosed when the pressure is greater than 160mmHg. 

How is high blood pressure diagnosed in cats?

Similar to methods used in humans, blood pressure can be measured with an inflatable blood pressure cuff. But in cats, it can be placed around the paw or tail. Your vets may instead use a Doppler blood pressure kit, where a cuff is placed around the arm and a lubricated probe is placed on the paw to get a reading. Both methods take just a few moments, are pain-free and are usually very well tolerated by cats. 

Blood tests are usually carried out if high blood pressure is found, with a thorough history of potential symptoms seen at home taken, alongside a full veterinary clinical exam, which will help determine the cause of hypertension and therefore lead to the treatment prescribed to help your cat. 

What are the symptoms of high blood pressure in cats?

Early signs of high blood pressure in cats are very subtle and difficult to spot at home. Usually signs only become apparent when significant damage has already been done. This is why routine monitoring of blood pressure is recommended for all cats over the age of 7 years or with underlying conditions. 

Some signs may include:

Bleeding into the eyes

  • Changes to eye appearance, either blood in the eye(s) or a fixed, dilated pupil. 
  • Bumping into objects
  • Sudden blindness

Bleeding into the brain 

  • Abnormal behaviour
  • Vocalisation
  • Disorientation
  • Depression
  • Ataxia (wobblinessor poor balance)
  • Seizures

Kidney damage

  • Reduced appetite
  • Vomiting 
  • Weight loss
  • Lethargy
  • Increased water intake 
  • Increased urination

Heart damage

  • Development of a heart murmur 
  • Heart failure 
  • Breathing changes
  • Lethargy

What are the main causes of high blood pressure in cats?

Chronic Kidney Disease (CKD) 

The most common cause of high blood pressure, it is estimated as the cause in 74% of cats. 

As well as being involved in filtering blood and waste removal, kidneys are also involved in controlling blood pressure by increasing sodium (salt) reabsorption, water reabsorption/ retention and sending chemicals to constrict or relax blood vessels. When the kidneys aren’t functioning correctly, we see the effects of inappropriate blood filtration, and the inability to maintain normal blood pressure. 

Hyperthyroidism 

A disease caused by an overactive thyroid gland is often associated with high blood pressure in cats. 

Thyroid hormones affect many body functions like heart rate and metabolism. The thyroid also has a direct effect on chemical levels controlling blood pressure within the kidneys. With too much thyroid hormone (as is the case with an overactive thyroid) many body functions speed up, including metabolism and heart rate. Higher heart rates force more blood into blood vessels, therefore, raising blood pressure. Increased blood pressure within the kidney leads to tissue damage and further inability for the kidney to perform as normal. Too much thyroid hormone can also alter the chemicals and mechanisms within the kidney that control blood pressure. 

Other causes 

  • Idiopathic – Around 20% of cats are found to have high blood pressure without another underlying cause. It is thought that a proportion of these, have very early kidney disease that is yet to be detectable on tests, but for a proportion, the condition will truly be a primary problem. 
  • Stress – This is a cause of high blood pressure in cats, even being in a veterinary clinic can TEMPORARILY lead to stress-induced hypertension. This is why it is important to take a range of blood pressure readings over a period of time, keeping the clinic quiet and calm to make it as accurate as possible. This ensures that true hypertension is diagnosed and not misinterpreted. 
  • Heart disease- Hypertrophic cardiomyopathy is another common condition in cats that leads to the heart being enlarged and thickened, working less efficiently. 
  • Diabetes (less commonly) – Diabetes when untreated, results in high sugar levels in the blood which in turn can lead to pressure builds up. Diabetes can also scar the kidneys leading to salt and water retention which in turn raises blood pressure. 
  • Obesity – Obesity is a risk factor for high blood pressure just as it is in humans. Amongst other factors, fat can accumulate in blood vessels making them narrower, less elastic and less reactive to hormones that constrict and relax them in normal processes controlling blood pressure. Obesity also affects the efficiency of the heart to pump blood around the body leading to high pressures which puts your cat at risk of stroke, heart disease and diabetes. 
  • Medication – Some medications can affect blood pressure. 

Why should we be worried about persistent high blood pressure in our cats?

Consistently high blood pressure in our cats is damaging to our cat’s bodies and organs. Early detection by routine annual monitoring in older cats can protect their vision and organs keeping them healthy for longer. Monitoring blood pressure at least twice yearly in those with other illnesses commonly associated with developing high blood pressure such as heart disease, obesity, hyperthyroidism, and diabetes is strongly recommended to prevent the worsening of the condition and damage to organs. 

If you suspect your cat may be suffering from high blood pressure or you would like to book a routine checkup to keep your cat healthy, contact your vet and let them know. 

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