GUEST COMMENTARY: The meter says you are hypertensive? Take the test again

Hypertension or high blood pressure is a condition that can linger in the body undiagnosed for a long time. During that time the high force of blood against blood vessels is causing damage that can affect any organ of the body.

Undiagnosed and untreated high blood pressure can affect the heart, resulting in failure, the brain causing a stroke, kidneys failing, or the eyes going blind. The list of likely health outcomes of untreated high blood pressure are as many as the organs in our body.

Hypertension is normally diagnosed by measuring blood pressure during a visit to a clinician. However, treatment should never be based on a single measurement. Experienced clinicians will ask patients to return for monitoring several times before starting treatment, and there is good reason for this.

Studies in developed countries have shown that one out of every four people who have a raised blood pressure the very first time it is measured in a clinical setting are actually not hypertensive.

This is referred to as ‘white coat hypertension’. The name implies that the presence of the clinician (often in a white coat) generates anxiety in the patient, raising the blood pressure. If this single measurement is used to treat a patient, then a lot of unnecessary treatments would be handed out. This would not only waste money, but these drugs also have side effects that people without hypertension need not bear.

A study in Tanzania investigated the value of repeated blood pressure readings in 1,315 people ages 25-64 years old, and the startling findings were published in the Journal of Hypertension in 2003. The study reported that half of the people who would had been diagnosed as having high blood pressure on the first visit were found to have normal blood pressure during the second visit three days later and several days after that.

The researchers suggested that the best way to diagnose high blood pressure was an average of three readings taken at least two days after the initial readings.

However, repeated blood pressure readings over a period of days may still be unable to detect high-risk people. In most healthy people, blood pressure goes down by about 10 per cent during the night. People whose blood pressure does not go down during the night are at increased risk of stroke and heart disease. These people would be detected if blood pressure can be measured both day and night.

Most of the developed world has adopted a more accurate way of diagnosing hypertension, and it is known as Ambulatory Blood Pressure Monitoring (ABPM).

ABPM refers to a procedure where blood pressure is measured over a 24-hour period as people go about their normal life. It uses a small digital blood pressure machine that is attached to a belt around the body and connected to a cuff around the upper arm.

It is small enough to allow for normal daily life and one can sleep with it on. It is slightly inconvenient for the participant, especially at night, but as it is used in the home environment, in the absence of a clinician, it provides highly reliable data

Dr Anthony Etyang and colleagues at the Kemri-Wellcome Trust Research Program in Kilifi in 2013 sought to find out whether 24-hour blood pressure monitoring could be used in a rural setting. Their work was published last month in the Journal of the American Heart Association

All the 986 study participants had their blood pressure measured three times over a five-minute period and the average of the last two measurements used to classify them as having normal or high blood pressure.

Those with high blood pressure and half of those with normal blood readings were requested to join a 24- hour ABPM study. They were fitted with a digital machine that would record their blood pressure every 20-40 minutes in a 24-hour period.

A total of 477 people had ABPM measurement done on them, 235 of whom had tested negative during screening. All the blood pressure monitoring was done through home visits by trained non-clinicians.

The study found that 26 per cent of the Kilifi population would be considered to have high blood pressure if the measurements from the readings on a single visit were used to diagnose the condition. However, 24-hour ABPM reported that only 17 per cent of the population had high blood pressure.

Using a single measure to determine the proportion of people in the population with hypertension almost doubled the prevalence. This is despite the fact that the researchers measured blood pressure three times on that single visit, discarding the first reading and averaging the second and third reading.

Interestingly, nearly half of those who were found to have high blood pressure using ABPM had tested negative when their blood pressure was measured using the normal screening method. These individuals would have been presumed to have normal blood pressure had ABPM not been done. Those aged 40 years and below were twice as likely to fall in this category than their older counterparts.

The researchers observed that there were people who tested positive during the screening test but had normal blood pressure using ABPM, what is referred to as ‘white coat hypertension’.

Translated to the population, the study tells us that out of every 100 people who test positive using the normal screening test, there will be four who in reality have a normal blood pressure.

“We need to consider discarding the current screening methods which are based on technology developed in 1890 by Riva-Rocci and Korotkoff. From our study, it appears that every age group would benefit from 24-hour ambulatory blood pressure monitoring,” said Dr Etyang.

However, the technology required to perform 24-hour ABPM is currently very expensive. Dr Etyang and colleagues are currently in the process of starting a study to investigate the cost effectiveness of ABPM as a diagnostic method. Also, during the community study, 174 out of 651 people refused to undergo ABPM, which suggests that the procedure may not be easily taken on by the population.

Both aspects of cost and acceptability need addressing in order to avoid unnecessary treatments of people with normal blood pressure and also reduce the human toll of young people suffering the consequences of untreated high blood pressure.