The most common causes of high blood pressure in cats are kidney disease and thyroid issues.
Why does kidney disease cause hypertension? Normal aging may lead to changes in kidney size. As kidneys shrink, it becomes harder for blood to filter through the organs. This can lead to an increase in blood pressure as blood gets backed up. At least one study has found that approximately sixty-five percent of cats with age-related kidney failure also have high blood pressure.
Why does hyperthyroidism cause hypertension? When the thyroid is over-producing hormones, many organs are affected — including the heart. The heart can pump faster and harder, eventually becoming enlarged. These three factors can cause a greater output of blood at higher pressure. As much as eighty percent of cats with hyperthyroidism also have high blood pressure.
Sometimes, high blood pressure appears without an underlying disease (like kidney failure or thyroid disease) present. This is known as “primary hypertension”. This type of high blood pressure is very common in humans, but is very rarely seen in cats. This doesn’t mean that it doesn’t exist — but secondary hypertension is far more common and will be ruled out first.
In order to treat hypertension, your veterinarian needs to first figure out what is causing the problem. Controlling the underlying problem may entirely control the blood pressure problem. Until the underlying problem is treated, your cat may need to take high blood pressure medication daily. While on medication, your cat should see the vet every few months for blood pressure checks.
The sooner hypertension is diagnosed, the sooner it can be treated. Some experts suggest screening cats ten years and older annually for high blood pressure. Blood pressure can be measured in cats more or less the same way it is in humans — using an inflatable cuff and an ultrasonic probe to measure systolic blood pressure. (Veterinarians cannot read diastolic blood pressure in cats without using an intravenous catheter, so they only read systolic blood pressure.)
A normal blood pressure reading for cats is between 110 and 160 mm Hg.