Measuring Blood Pressure at Home: What the Guidance Says

The American Heart Association (AHA) recommends home monitoring for all people with high blood pressure, to help their healthcare professional know whether treatment is working. It says home monitoring can also be used to confirm a diagnosis, but it does not replace regular doctor visits. The US Centers for Disease Control and Prevention (CDC) says evidence shows people with high blood pressure are more likely to lower it if they use self-measurement together with support from their health care team.

There is a second reason. The CDC notes that nervousness about having blood pressure taken, sometimes called white coat syndrome, can raise a reading, and that as many as 1 in 3 people with a high reading at the doctor's office may have normal readings outside it. In the UK, the NHS says a person with a high clinic result may be asked to monitor at home for a few days, return for another clinic reading, or wear a portable monitor for 24 hours to confirm the result. Background on what the numbers mean is in high blood pressure explained.

The AHA recommends an automatic, cuff-style monitor worn on the upper arm, and says wrist and finger monitors give less reliable readings. It advises choosing a monitor that has been validated, and asking a healthcare professional or pharmacist if you are unsure. The cuff must fit: a cuff of the wrong size produces an inaccurate reading, according to the AHA, which suggests measuring around the upper arm and choosing a monitor that comes with the correct cuff size.

The AHA also suggests taking the monitor to an appointment, so a professional can check it against the office equipment.

The AHA and CDC describe similar preparation. The AHA advises avoiding smoking, caffeinated drinks and exercise for 30 minutes beforehand, and emptying your bladder. The CDC adds avoiding eating or drinking for 30 minutes before.

• Sit with your back supported and both feet flat on the floor, legs uncrossed (CDC).
• Rest quietly for at least five minutes before measuring, without talking or using the phone (AHA).
• Rest your arm on a flat surface at heart level, with the cuff on bare skin, not over clothing (AHA and CDC).
• Take two readings one minute apart and record both (AHA). The CDC likewise suggests at least two readings, 1 or 2 minutes apart, at the same time each day.

The NHS says home readings are usually taken twice a day, in the morning and evening, for the number of days a doctor or nurse specifies. Either arm can be used, the AHA says, as there is usually not a big difference between them.

A single number reflects one moment. A log of readings over days gives a fuller picture, which the AHA calls the difference between a snapshot and a record over time. Averaging the readings smooths out the ups and downs of any single moment.

AHA News reported on a study of 316 adults who took two readings in the morning and two at night. The researchers wrote that "using the average of morning and evening readings, a minimum of three days are needed to reliably estimate out-of-office blood pressure and confirm a diagnosis of hypertension." That is one study's finding, and schedules vary. The NHS gives 135/85 as the level at which home readings are usually considered high, against 140/90 in clinic.

The AHA states that a single high reading is not an immediate cause for alarm. It suggests taking a second reading, writing down both and checking with a healthcare professional about whether there is a health concern or a problem with the monitor. It also states that only a doctor or other medical professional can confirm a high blood pressure diagnosis. The World Health Organization (WHO) makes a related point: individuals can measure their own pressure with automated devices, but an evaluation by a health professional is important for assessing risk. For the heart physiology behind these numbers, see how the heart works.

Sources agree on 180/120 mmHg as the level of concern, but they word the response differently. The AHA says that if readings are suddenly higher than 180/120 mmHg, wait at least one minute and test again, and if they are still very high, contact your healthcare professional immediately. If a reading is above 180/120 and you have symptoms such as chest pain, shortness of breath, back pain, numbness, weakness, a change in vision or difficulty speaking, the AHA says to call 911, the US emergency number, and not wait to see whether the pressure comes down. WHO says very high pressure, usually 180/120 or higher, can cause symptoms including severe headache, chest pain, dizziness and blurred vision, and that anyone with such symptoms and a high reading should seek care immediately.

These figures come from specific organisations. Thresholds and instructions can differ between countries and guidelines, and the NHS pages reviewed here give no number for very high home readings, directing people to a GP, nurse, pharmacist or the NHS 111 advice line instead.

Take your monitor and your log to a routine appointment so a professional can review both. Ask a clinician before changing any medicine in response to a home reading, and do not stop treatment because a number looks good. If a reading is very high with chest pain, breathlessness, weakness, numbness, vision change or difficulty speaking, treat it as an emergency and use your local emergency number, since these differ by country. See stroke signs and heart attack signs.

Home readings can help clinicians see blood pressure over days rather than minutes, and good technique with a validated, correctly sized upper-arm cuff makes the numbers more useful. Averages across several readings carry more weight than any single one, and only a clinician can diagnose hypertension. A reading above 180/120 with symptoms is a medical emergency in the guidance cited here.