Tuesday March 29 2011
A third of hypertension patients had normal blood pressure when measured in non-GP environments
“Doctors cause a third of stubborn high blood pressure,” reported the BBC News. The news service reports that some cases of hard-to-treat high blood pressure may actually be caused by patient nervousness at being seen by a doctor.
The news is based on a Spanish study which compared blood pressure measurements taken in a doctor’s surgery and measurements gathered using a 24-hour monitoring device in people believed to have resistant hypertension. Resistant hypertension was defined in this study as high blood pressure that had not responded to concurrent use of three or more high blood pressure medications.
The study found that 37% of patients with resistant hypertension (based on the doctor’s surgery measurements) actually had blood pressure within the normal range when it was measured with 24-hour monitoring. This suggests that an anxious response to being in a doctor’s surgery may affect a proportion of patients’ blood pressure readings.
At present, NICE recommends that raised blood pressure is confirmed on at least two further readings at a separate time. However, recent draft recommendations issued by NICE have called for the introduction of home-based or ambulatory blood pressure monitoring to confirm diagnoses of high blood pressure. These are expected to be approved later this year.
Where did the story come from?
The study was carried out by researchers from The University of Barcelona, and it was funded by Lacer Laboratories, Spain.
The study was published in the peer-reviewed medical journal, Hypertension.
The Daily Mail reported that “thousands are wrongly treated for high blood pressure”. However, this should not be assumed on the basis of this research alone: the study only looked at a subgroup of people with high blood pressure - those who had been diagnosed with resistant hypertension, i.e. high blood pressure despite being treated with multiple anti-hypertension medications.
Also, the study did not assess whether these people had originally been misdiagnosed with hypertension or whether their medication was actually just working to control what would have otherwise been high blood pressure. The study was also in Spain, where the medical practices for treating hypertension may vary from those used in the UK.
The Daily Mail and the BBC News did highlight draft NICE guidelines which propose that home or ambulatory blood pressure monitoring should be used to confirm any initial diagnosis of hypertension.
What kind of research was this?
The researchers say that a proportion of the high blood pressure measurements taken at the doctor’s office may be affected by the “white coat effect”, where a person’s blood pressure may be affected by the anxiety they feel while visiting the doctor. In turn, these readings may go on to form the basis of a patient’s treatment strategy.
This was a cohort study, which followed patients with persistent resistant hypertension (high blood pressure). It compared their blood pressure readings, which were taken in a doctor’s office and obtained using a blood pressure monitoring device that could measure their blood pressure as they went about their daily lives. In this study, resistant hypertension was defined as blood pressure that remained above the target threshold (140/90mmHg) despite the concurrent use of three hypertensive agents at full doses, one of them being a diuretic.
The ambulatory blood pressure monitoring (ABPM) used in this study was performed using a device that was worn by the patient over a 24-hour period in order to measure their blood pressure in 20-minute intervals throughout the day. This method allows doctors to assess fluctuations in blood pressure and examine whether blood pressure remains high for extended periods of the day.
The Spanish researchers say that these devices are currently used in a small proportion of referred patients. They wanted to use this technology to record data from a large group of patients with hypertension according to measurements taken in their doctor’s office.
What did the research involve?
The study was carried out in Spain, and recruited patients who were registered with the Spanish Ambulatory Blood Pressure Monitoring (ABPM) registry. This registry was set up to promote the use of ABPM in clinical practice. The patients were recruited from this registry if:
- they had enough information regarding office blood pressure measurements and had ABPM data of good quality.
- they had resistant hypertension that was uncontrolled despite using more than three blood pressure medications (including one diuretic).
- their doctor’s office BP measurements were over 140 and/or 90 mm Hg – the commonly accepted threshold for defining high blood pressure.
In total, the researchers analysed data on 8,295 patients with resistant hypertension (this population with resistant hypertension was approximately 12% of patients with hypertension).
The patients wore the ABPM device for 24 hours, and their blood pressure was measured every 20 minutes. The majority of patients’ measurements using this device had been on working days, during which the participants were asked to maintain their usual activities. Daytime and night time periods were defined according to the patient’s self-reported data of going to bed and getting up times.
The researchers classified patients based on how their blood pressure during the night related to their daytime BP (expressed as a percentage). People were classified as:
- extreme dippers if their systolic or diastolic BP fell by more than 20% in the night
- dippers if it fell between 10 and 20%
- non-dippers if it fell between 0 and 10%
- risers if BP increased during night time
The researchers also looked at data on the patients’ age, sex, height, weight, smoking status and whether they had diabetes. All of these factors may have influenced their blood pressure.
What were the basic results?
Using the ABPM data, the researchers found that 5,182 of the 8,295 patients (62.5%) who had been diagnosed with resistant hypertension in a clinical setting had true resistant hypertension when assessed using ambulatory 24-hour blood pressure monitoring and cut-off values of more than 130 and/or 80mmHg. The other 3,113 patients (37.5%) showed BP values below this cut-off and were classified as having “white coat” resistant hypertension.
The patients with true resistant hypertension tended to be younger, male, have a longer duration of hypertension, and have a worse cardiovascular risk profile. For example, being smokers, having diabetes and having heart or kidney damage.
The researchers found that the group with true resistant hypertension had a higher proportion of ‘riser’ pattern patients (i.e. BP increased during the night) than the group with white coat hypertension. (22% vs. 18%; p<0.001).
How did the researchers interpret the results?
The researchers estimated that “resistant hypertension is present in 12% of the treated hypertensive population”, but say that “among them more than one third have normal ambulatory blood pressure”. They emphasise a need to use ambulatory blood pressure monitoring in order to make a correct diagnosis of resistant hypertension and to manage this condition.
Although they found that a worse cardiovascular risk factor profile was associated with true resistant hypertension, they emphasised that this association is weak.
This research in a relatively large Spanish cohort has assessed the prevalence of true resistant hypertension in a population that had been diagnosed with this condition using blood pressure measurements taken in the doctor’s surgery. The observation that approximately a third of the assessed population’s blood pressure was within a normal range over the 24-hour period suggests that diagnoses should take into account “white coat hypertension”, or blood pressure changes as a response to being in the doctor’s surgery.
Current UK guidelines recommended that an initial diagnosis of high blood pressure is confirmed on at least two further surgery visits. However, The National Institute for Health and Clinical Excellence (NICE) has recently issued revised draft guidance for hypertension. It recommends that 24-hour ambulatory blood pressure monitoring (ABPM) should be used to confirm the diagnosis of hypertension if the first and second blood pressure measurements taken during a consultation with a doctor are both higher than 140/90mmHg. While these proposed changes in diagnoses are still subject to revision, it is expected that they will be introduced later this year.