My heavily pregnant wife went to see her GP last week for a routine check-up. During her appointment, the doctor measured her blood pressure and got a high reading. My wife was surprised by this and insisted that she felt fine, so he took a second reading. But that was high, too. The doctor was concerned enough to book her a follow-up appointment.
We visit our doctor for expert advice about our health but what if the blood pressure readings they take are not always accurate? A growing body of evidence suggests that patients who measure their own blood pressure get more accurate readings.
As it turned out, my wife was fine, but cases like this raise questions about how blood pressure should best be measured.
What is blood pressure?
Your blood pressure level fluctuates with every heartbeat, with a peak in pressure during the heart’s contraction phase (known as systole) and a drop during the relaxation phase (known as diastole). High blood pressure – also known as hypertension – is usually defined as a systolic blood pressure of more than 140mmHg and/or a diastolic pressure of more than 90mmHg.
Hypertension affects about one in three adults in the developed world – that’s 16m people in the UK and nearly 80m in the US. Around one in every 33 women will develop hypertensive complications during pregnancy.
A silent killer
Hypertension is often described as a “silent killer” since most patients who have it don’t have any symptoms, but the implications of living with sustained high blood pressure can be very serious. Indeed, it’s known to be one of the most important risk factors for heart attack and stroke. Women who have hypertension during pregnancy can develop pre-eclampsia, which is associated with increased risk of maternal and foetal death, although this is very rare.
Accurate measurement is obviously important, although not always straightforward as blood pressure levels fluctuate throughout the day and can easily change as a result of stress, physical activity and even talking. So, being late for your doctor’s appointment, running to get there on time or apologising for being late while the doctor measures your blood pressure could all cause an unexpectedly high reading. But these one-off, elevated readings don’t necessarily mean that you are at a higher risk of having a stroke or complications during pregnancy.
More readings are better
The answer research is pointing to is to measure your blood pressure repeatedly throughout the day or week, and take an average of these readings. You can do this yourself, using monitors which are widely available from pharmacies, supermarkets and online retailers. Alternatively, a doctor may give you a monitor which takes readings automatically throughout the day and night. This approach is generally considered to be the gold standard measure of blood pressure.
The white coat effect
So what happens when readings taken at home or with a 24-hour monitor don’t agree with those taken by your doctor in the clinic? People with high (greater than 140/90 mmHg) clinic readings but normal home or 24-hour blood pressure readings are thought to have “white coat hypertension”. These people are sometimes given more intensive blood pressure lowering drugs than may be necessary. But recognising which patients will react to a white coat is difficult if only one-off measurements from a GP consultation are available. Also, it’s probably not reasonable to expect everyone to measure their own blood pressure and report to a doctor when the readings are repeatedly high.
New research suggests that it may be possible to predict whether a person is going to have higher or lower blood pressure at home based on information routinely available in a GP surgery setting. This research suggests that being a man, being overweight or smoking may predict those people who are more likely to have higher blood pressure readings at home. There are also ongoing studies exploring whether these factors could be used by doctors to decide which people are most likely to benefit from home or 24-hour monitoring to guide treatment decisions.
Should you ignore your GP’s readings?
While the measurements taken by a doctor may not be perfect, they could be the first step to understanding your true underlying blood pressure level. Measuring it yourself as well, may assist doctors in making better treatment decisions that help you avoid a stroke or complications during your pregnancy.
Article doi: 10.1161/HYPERTENSIONAHA.115.07108