High blood pressure in dogs and cats: when to measure it

Blood pressure is the force with which blood flows through the arteries. It is expressed with two numbers, the systolic when the heart contracts and the diastolic when it relaxes, measured in millimetres of mercury. In veterinary practice the value that guides decisions is almost always the systolic, because it is the one measured most reliably with the non invasive tools available in the clinic.

The problem is not a single slightly high reading during a visit, but a pressure that stays elevated over time. A force that is too strong and continuous wears down the wall of the smallest and most delicate vessels, those of the retina, the renal glomerulus, the brain and the heart muscle. The damage accumulates gradually, which is why the disease is often called silent: by the time a clinical sign appears, the tissue has usually already suffered.

Hypertension hits four areas in particular. Knowing them helps explain why apparently unrelated symptoms lead the vet to ask for a pressure reading.

Sudden blindness from retinal detachment is the most dramatic and, sadly, frequent presentation in the older hypertensive cat. A cat that bumps into furniture, has permanently dilated pupils or shows blood in the front of the eye should be treated as an emergency: lowering pressure quickly can sometimes recover part of the vision, but only if action comes early.

Measuring pressure at every visit of a young, healthy animal makes little sense and often produces false alarms from stress. It becomes a sensible step in well defined situations, where the chance of finding high values is real and where an early diagnosis genuinely changes management.

• Cats aged seven and over, especially with diagnosed or suspected chronic kidney disease or hyperthyroidism.
• Dogs with kidney disease, Cushing's syndrome or other known endocrine disorders.
• Any animal with sudden blindness, blood in the eye or permanently dilated pupils.
• Unexplained neurological signs, such as disorientation or seizures appearing in later life.
• Before and during treatment with drugs that may affect blood pressure, as directed by the vet.
• As a periodic check in an animal already diagnosed as hypertensive, to confirm the treatment is working.

The clinic measurement uses an inflatable cuff placed on a leg or the tail, connected to a device that detects blood flow. The procedure is painless, but it needs calm and a precise method, because stress raises the values and creates a white coat effect in animals too.

1. 1

   Settling in

   The animal spends five to ten minutes in a quiet room, ideally in the owner's arms, before starting. A cat allowed to come out of the carrier on its own, without restraint, gives more realistic values.

2. 2

   Choosing the cuff

   The cuff must have the right width for the limb circumference. Too narrow overestimates the pressure, too wide underestimates it. The correct choice is part of the quality of the reading.

3. 3

   Repeated readings

   At least five or six consecutive readings are taken, the first and any outliers are discarded, and an average is calculated. A single value is not a diagnosis.

4. 4

   Recording the context

   The clinician notes whether the animal was agitated, which limb was used and the time. These details make readings taken on different days comparable.

5. 5

   Examining the eyes

   When pressure is high, the vet checks the back of the eye: the retina reveals whether damage is already under way and for how long.

If the values stay high in a repeated and consistent way, the next step is to look for the underlying disease with blood and urine tests, and to assess the target organs. The decision to start treatment depends on the pressure level, the presence of organ damage and the cause found, and it is a choice for the vet, not an automatic reaction to a number.

Once diagnosed, hypertension is a condition to manage over time, not to fix once and for all. Treatment lowers the risk of future damage, but it needs regular checks to confirm the pressure has come down into the right range without dropping too far.

1. Treat the underlying disease, because controlling the kidney or thyroid often improves the pressure as well.
2. Keep to the scheduled checks, usually more frequent at the start of treatment and then spaced out once values are stable.
3. Watch the animal's sight every day: changes in how it moves around the home can signal an eye problem.
4. Keep a log of the readings, so you and the vet read the trend and not just the single figure.
5. Never change the doses on your own: a pressure that is too low is as dangerous as one that is too high.

The owner's role is not medical but one of constant observation and continuity. Reporting promptly a change in visual behaviour, an increase in thirst or an episode of disorientation lets the treatment be adjusted before the damage becomes serious. The quality of long term management depends heavily on this daily attention.