Labile (fluctuating) blood pressure: why readings vary and how it is assessed in the UK

The word labile means changeable. Labile hypertension is used by some clinicians to describe blood pressure that swings between normal and high readings rather than staying steadily raised. The NHS pages and the British Heart Foundation (BHF) material used for this guide do not use the term as a separate diagnosis. They describe the things behind it: blood pressure naturally varies, a single reading may not reflect your usual level, and the way it is measured affects the result.

The BHF explains that blood pressure can go up and down a lot during the day. That is why high blood pressure usually needs to be confirmed by checking more than once rather than on a single occasion, and why a clinician may ask you to monitor at home or wear a 24-hour monitor to build up an average picture.

The BHF says that when people have their blood pressure checked in the clinic it can be higher than expected, especially if they feel nervous or anxious. This is the reason a high clinic reading is often followed by home monitoring to see whether the pressure is also high in everyday settings.

The NHS lists things that increase the chance of having high blood pressure, including age, close relatives with high blood pressure, ethnicity, an unhealthy diet especially one high in salt, being overweight, smoking, drinking too much alcohol and feeling stressed over a long period. These affect your usual level rather than explain a single reading, but they are the factors a clinician looks at.

Measurement technique also matters. The NHS describes the standard blood pressure test as sitting down, rolling up your sleeve, resting your outstretched arm on a table and relaxing with an armband around the upper arm, and says the test may be done a couple of times to make sure the measurement is accurate.

The NHS says high blood pressure does not usually cause any symptoms and many people have it without realising. Rarely, it can cause headaches, blurred vision or chest pain, and the only way to find out whether you have it is to get your blood pressure checked.

The NHS says to get a blood pressure check at a pharmacy or GP surgery if you think you might have high blood pressure or be at risk, or if you are 40 or over and have not had it checked for more than 5 years. It advises getting help from NHS 111 if you often have headaches or blurred vision, have chest pain that comes and goes, or have other symptoms you are worried could be caused by high blood pressure. Call 999 if you have sudden chest pain or discomfort that does not go away, pain that spreads to the arm, neck, jaw, stomach or back, or chest pain with feeling sweaty, sick, light headed or short of breath, because you could be having a heart attack.

The NHS says that if a blood pressure test suggests you might have high blood pressure, you may be asked to use a monitor at home to check your blood pressure regularly over the next few days, return to the GP surgery a few days or weeks later to have it checked again, or wear a portable monitor that takes regular readings over 24 hours. These can confirm whether you have high blood pressure.

The BHF describes the 24-hour monitor as ambulatory blood pressure monitoring, or ABPM, and says that looking at all your readings over a few days lets your GP work out your average blood pressure. It adds that the GP may run other tests, such as blood tests to check cholesterol and kidney function or an electrocardiogram (ECG) to check heart rhythm. At home, the NHS says to take your reading, note the numbers, wait 1 minute and repeat, usually twice, once in the morning and once in the evening, for the number of days your doctor or nurse tells you.

The NHS says that if blood pressure is too high it puts extra strain on the blood vessels, heart and other organs such as the brain, kidneys and eyes, and that untreated it can increase the risk of heart disease, heart attacks, strokes, heart failure, kidney disease and vascular dementia. It stresses that lowering blood pressure even a small amount can help reduce the risk of these problems.

This is why readings that are sometimes normal and sometimes high should not be dismissed. A normal reading on one day does not cancel out a high one on another, and the average of several readings is the figure a clinician will use. Keep a diary of your readings, which the BHF says helps your healthcare team spot patterns and can be motivating to see how your blood pressure improves.

The NHS lists lifestyle steps that can help lower blood pressure: a healthy, balanced diet, regular exercise with at least 150 minutes a week, losing weight if overweight, not eating too much salt, not drinking too much alcohol (avoiding more than 14 units a week on a regular basis), not drinking too much caffeine and not smoking.

A GP will usually prescribe medicine if your blood pressure is very high, you are at higher risk of problems such as a heart attack or stroke, or your blood pressure is still high after lifestyle changes. The NHS says there are many different medicines, that the choice depends on how high your blood pressure is, your age and your ethnicity, that most are tablets taken once a day and that you may need more than one. Do not stop or change medicines because of a single reading without talking to your GP or pharmacist.

The BHF says that if you are a healthy adult aged 40 to 74 it is a good idea to get your blood pressure checked every 5 years, and that you may be invited for an NHS Health Check in England once you turn 40. If you have been diagnosed with high blood pressure and it is under control, you will normally be monitored yearly, with a review of your medicines, and more often when you start new medicines or change doses. It also notes that schemes such as Blood Pressure @home in England and Scale-Up BP in Scotland support home monitoring, which you can ask your GP about.

Blood pressure checks are available at pharmacies and GP surgeries, and the NHS says some pharmacies may charge for a check while free checks are offered to people aged 40 or over at many. Home monitors can be bought privately, and the NHS says machines may differ slightly so you should follow the instructions. Bring your readings diary to appointments so your clinician can judge your average.