White-coat hypertension: high readings in clinic, normal at home

Blood pressure is not a fixed number. It rises and falls through the day and night, and the British Heart Foundation notes that it is normal for it to go up while you are moving about. Being measured by a healthcare professional is, for many people, a stressful moment in itself, and the reading can climb as a result. The "white-coat effect" is the term for readings that are higher at a surgery or clinic than they are at home.

A patient information leaflet from a hospital trust says around 1 in 4 people have this effect. NICE gives it a precise working definition for clinicians: a discrepancy of more than 20/10 mmHg between clinic readings and the average daytime reading from ambulatory or home monitoring, at the time of diagnosis.

The term white-coat hypertension is generally used when the clinic readings would meet the threshold for hypertension while readings taken in everyday life do not. The concept is simple, but it needs measurements outside the clinic to identify, which is why monitoring is the heart of the diagnosis.

Treating a number that is only high in clinic could mean taking tablets you do not need. NICE recommends confirming hypertension with out-of-clinic measurements before a diagnosis is made, which protects people from that outcome.

The reverse problem exists too. NICE defines masked hypertension as normal clinic readings (under 140/90 mmHg) alongside higher readings when measured outside the clinic. Someone reassured by a normal surgery reading could miss a genuine problem. Because the white-coat effect and masked hypertension are two sides of the same measurement gap, a clinician may suggest monitoring in either situation.

NHS information stresses what is at stake if blood pressure is truly high and untreated: extra strain on blood vessels, heart and organs including the brain, kidneys and eyes, and a higher risk of heart disease, heart attacks, strokes, heart failure, kidney disease and vascular dementia. Lowering blood pressure even a small amount can help reduce those risks, which is why getting the diagnosis right is worth a few days of careful measuring.

The NHS explains that if a check suggests you might have high blood pressure you may be asked to use a monitor at home for a few days, return to the surgery for repeat checks, or wear a portable monitor that takes regular readings over 24 hours. NICE guideline NG136 sets out the standard approach.

A hospital trust leaflet advises using a validated monitor and points to the British and Irish Hypertension Society website for a list of validated devices; it says it does not recommend any particular brand. It suggests recalibrating or replacing monitors following the manufacturer instructions, usually every 2 to 4 years, and replacing one that is more than 5 years old.

The NHS notes that home readings of 135/85 or higher are usually considered to indicate high blood pressure, compared with 140/90 or higher when checked by a healthcare professional. Those two thresholds differ because everyday readings tend to be lower than clinic readings.

• Sit quietly with your back supported and arm resting at heart height before you start.

• Take two readings one minute apart, morning and evening, and record both.

• Bring the record, and ideally your monitor, to your appointment so that the device can be checked against the surgery machine.

• Do not change any medicine you already take on the basis of home readings without discussing it first.

If monitoring shows normal readings outside the clinic, hypertension is not diagnosed, but that is not the end of the story. NICE advises considering more frequent checks if clinic blood pressure is under 140/90 mmHg but still raised. People who have a large clinic-home discrepancy may be offered ABPM or HBPM alongside clinic readings, as NICE recommends for those with a white-coat effect or masked hypertension.

Lifestyle advice applies to everyone. The NHS suggests a healthy balanced diet, at least 150 minutes of exercise a week, losing weight if overweight, avoiding too much salt, keeping to no more than 14 alcohol units a week on a regular basis, limiting high-caffeine drinks, and not smoking.

If high blood pressure is confirmed, NICE describes when medicine is offered: it is offered with lifestyle advice to adults of any age with persistent stage 2 hypertension, and discussed for those under 80 with stage 1 hypertension who have conditions such as established cardiovascular disease, kidney disease or diabetes, or a 10-year cardiovascular risk of 10% or more. These decisions are individual and belong with your clinician.

High blood pressure usually causes no symptoms. The NHS says that rarely it can cause headaches, blurred vision or chest pain, and 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 get sudden chest pain or discomfort that does not go away, pain spreading to the arm, neck, jaw, stomach or back, or chest pain with sweating, sickness, light-headedness or breathlessness, as these could be a heart attack. NICE also describes a clinic reading of 180/120 mmHg or higher together with signs such as new confusion, chest pain, signs of heart failure or retinal haemorrhage as a reason for same-day specialist assessment.

In the NHS this is normally handled in primary care: your GP surgery, practice nurse or pharmacist can arrange home or 24-hour monitoring. In England the blood pressure@home scheme supports home monitoring, and healthy adults aged 40 to 74 are usually invited to an NHS Health Check every five years that includes a blood pressure check, according to the British Heart Foundation. Many pharmacies offer free checks for people aged 40 or over.

Private cardiology or health-check services can also offer ambulatory monitoring and a specialist opinion. Most people with a straightforward white-coat pattern do not need a specialist, but a private route may suit someone who wants quicker access to a 24-hour recording or has other heart risk factors. Ask what is included and whether the results will be shared with your GP, and ask for any fee to be itemised.