A significant difference in the blood pressure (BP) value of a patient taken by different health workers has been a subject of discussion among health workers. This study investigated the variations between usual-care and guideline-concordant BP measurement protocols and evaluated the implications of the disparities on diagnosis and treatment decision.
A cross-sectional study was conducted among 206 participants. The usual-care and guideline-concordant BP readings taken from each participant by the regular clinic nurses and research-trained nurses, respectively, were obtained.
Majority of the regular clinic nurses following the usual-care protocol used the left arm for BP measurement (59.7%). The systolic BP (SBP) and diastolic BP (DBP) readings were higher on the right arm in 55.3% and 39.2% of the participants, respectively. The mean guideline-concordant BP was 7.67 mmHg higher than the mean usual-care for SBP (
The usual-care and guideline-concordant BP measurement protocols were significantly different, and the disparity had significant consequences on the diagnosis and treatment of hypertension. Health workers should strictly adhere to the guidelines on BP measurement to avoid mismanagement of patients.
Hypertension is an enormous independent risk factor for cardiovascular disease, stroke and renal disease,
In a typical Nigerian primary care clinic, BP is assessed by health workers as part of an initial or ongoing assessment of patients. Unfortunately, the measurement of BP done by the primary health care workers seldom adheres to the guideline-concordant BP measurement protocol.
Previous Nigerian studies have focused on sphygmo-manometer-related errors in BP measurement,
Participants’ BP is measured by a medical or paramedical staff during the usual clinical examination.
Participants’ BP is measured by a trained research staff (nurse) according to the recommended guidelines for taking BP.
The study was carried out at the GOPC of a tertiary hospital in south west Nigeria. Nigeria is a country with a weak primary health care system. The frail state of Nigerian primary health care places a heavy burden on tertiary hospitals. The problem is more pronounced in places where secondary care is also weak or mostly provided by the private sector. This results in inversion of the pyramidal distribution of patients such that the majority of patients are seen at the tertiary level. In response to this development, the GOPC in all Nigerian tertiary hospitals has family physicians who were trained to manage patients at primary and secondary care centres attending to these primary care patients. This makes the GOPC of a tertiary hospital in Nigeria a first contact facility for any type of patient.
The tertiary hospital where the study was conducted also serves as a referral centre for other lower cadre hospitals. The GOPC of the tertiary hospital is one of the primary care clinics of the hospital. It is run by consultant family physicians and resident doctors in Family Medicine. The general outpatient clinic (FOPC) of the hospital has a relatively large adult patient population and the health care providers take high numbers of BP measurements daily as part of the routine care of patients.
This was a hospital-based, cross-sectional study.
The study population comprised adult patients aged 18 years and above who attended the GOPC during the study period. A monthly average of 1168 patients was diagnosed at this clinic.
All adult patients aged 18 years and above with or without a prior history of hypertension were included in the study.
Patients who had eaten within 30 min of BP assessment.
Patients who had their BP checked for more than 10 min by the regular clinic nurses at the time of entering the consulting room.
Patients who had smoked or taken coffee within 30 min of BP assessment.
Patients with major psychiatric illness or severe illness who required urgent attention.
The formula for calculating sample size for a paired data was used,
difference = clinically meaningful difference between usual--care and guideline-concordant methods. A difference of 10 mmHg between the measurements from the two methods will be assumed to be a clinically meaningful difference. The mean usual-care systolic BP (SBP) and diastolic BP (DBP) values obtained from a previous study were 143 mmHg and 90 mmHg, respectively.
Zβ = standard normal deviate that corresponds to power (80% power = 0.84)
Zα/2 = standard normal deviate that corresponds to a two-tailed significance level (1.96 for α = 0.05).
Therefore,
However, in order to allow for missing data, an attrition value (10% of the estimated minimum sample size) was added. The adjusted sample size (
A systematic random sampling technique was used to select 206 subjects attending the GOPC over a period of 1 month. With a monthly average of 1168 patients, the sampling interval was (1168/206) = 5.67. Therefore, every fifth patient presenting at the GOPC and who met the selection criteria was enrolled in the study. The first subject was selected by balloting once at the outset of the study after which every fifth eligible patient was recruited. The process was repeated on subsequent days until the sample size was achieved.
The exclusion criteria were ruled out through review of participants’ case notes and interviews. Information was obtained by the authors using an interviewer-administered questionnaire (see
Two research assistants who were registered nurses were specifically trained in guideline-concordant BP measurement methods using a protocol that followed JNC 7 recommendations using the same validated mercury sphygmomanometers that were available in the clinics for BP measurements.
The usual-care BP was measured using the mercury sphygmomanometer employing the auscultation method by the regular four clinic nurses at the time of the study. Patients who were eligible for the study were recruited based on the sampling technique at this point. They were called into the consulting rooms to see the research-trained nurse assistants. Informed consent was obtained from eligible patients by the research nurse assistants. Participants had their BP re-assessed according to the standard protocol (The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure [JNC 7] guideline) using the mercury sphygmomanometer employing the auscultatory method.
The participant’s arm was bared up to the shoulder. Arm length was measured from the acromion to the olecranon process using a tape measure. The midpoint of the arm was marked using an eyebrow pencil. The arm circumference was measured horizontally at the midpoint mark by using the tape measure with the arm in a relaxed posture (to ensure the tape measure is at the proper tension). The appropriate size BP cuff was used based on the arm circumference (24 cm – 35.5 cm = medium cuff; 36 cm – 42 cm = large cuff; > 42 cm = extra-large cuff).
The participant then sat comfortably in a chair with back support and both feet flat on the floor. The participant’s brachial artery was marked using an eyebrow pencil. The cuff was placed snugly on the arm with the inflatable inner bladder centred over the brachial artery and the lower edge of the cuff about 2.5 cm above the natural crease of the elbow. After the cuff had been properly placed, the participant was instructed to sit quietly without talking, eating, completing paperwork or crossing his or her legs for 5 minutes.
The cuff was inflated to 20 mmHg above that pressure at which the radial artery became impalpable. Systolic BP and DBP were measured via auscultation at the Korotkoff sound I and V. After a 2-min rest time, BP measurement was repeated. Between measurements, patients were asked to raise their arm for 5 seconds and rest their arm at the heart level for an additional 25 s to eliminate auscultation gap. The average of the two readings constituted the guideline-concordant BP.
The time between usual-care and guideline-concordant BP assessment was kept to 10 min at the most so as to reduce the effect of time on BP values. Previous studies indicated that a time lag of fewer than 10 min does not have any significant effect on the BP value.
The study lasted for a period of 1 month.
The data were analysed using the Statistical Package for Social Sciences (SPSS) version 21.0 program. Both descriptive and inferential statistics were used. For descriptive data, means ± SD values were used for continuous variable and percentages for categorical variables.
In a previously normotensive respondent or uncontrolled BP in a known patient with hypertension, BP ≥ 140/90 mmHg was considered as ‘hypertension’ in patients without diabetes or chronic kidney disease or BP ≥ 130/80 mmHg was considered as ‘hypertension’ in patients with chronic kidney disease or diabetes.
The difference between means of SBP and DBP in the guideline-concordant and usual-care group was assessed using the paired
The protocol was approved by the Health Research Ethics Committee of the hospital with protocol number FMCA/470/HREC/11/2016 and registration number FWA/Q0018660/02/28/2017. A sample of written consent is attached (see
The financing and sponsoring of the project were wholly at the expense of the researchers.
Two hundred and six participants were recruited for the study. The mean age of the respondents was 48.16 ± 14.45 years and 59.7% of them were female. The more frequently used arm for usual-care BP measurement was the left arm (59.7%). The range of the difference between guideline-concordant BP and usual-care BP was −24 mmHg to 90 mmHg for SBP and −38 mmHg to 44 mmHg for DBP (
Baseline demographic and clinical characteristics.
Variable | Category or range | Frequency (%) or mean ± SD |
---|---|---|
Age (years) | 20–83 | 48.16 ± 14.45 |
Gender | Male | 83 (40.3) |
Female | 123 (59.7) | |
Arm used for usual-care BP | Right | 89 (43.2) |
Left | 117 (59.7) | |
Time between usual-care and guideline-concordant BP check (minutes) | 2–10 | 7.84 ± 2.01 |
Mean usual-care systolic BP (mmHg) | 70–220 | 123.22 ± 25.06 |
Mean guideline-concordant systolic BP (mmHg) | 90–250 | 130.89 ± 24.97 |
Mean usual-care diastolic BP (mmHg) | 40–150 | 74.62 ± 14.22 |
Mean guideline-concordant diastolic BP (mmHg) | 40–136 | 81.76 ± 14.92 |
Mean of difference between guideline-concordant systolic BP and usual-care systolic BP (mmHg) | −24 to 90 | 7.67 ± 15.06 |
Mean of difference between guideline-concordant diastolic BP and usual-care diastolic BP (mmHg) | −38 to 44 | 7.14 ± 13.08 |
SD, standard deviation; BP, blood pressure.
The guideline-concordant SBP and DBP readings were higher for the right arm than the left arm in most of the respondents (
Guideline-concordant systolic and diastolic blood pressure measurement of both arms.
Both guideline-concordant SBP and DBP measurements were greater than usual-care SBP and DBP measurements in 64.6% of the respondents (
Comparison of usual-care and guideline-concordant blood pressure measurement.
The mean guideline-concordant SBP was 7.67 mmHg higher than the mean usual-care SBP (p ≤ 0.001), while the mean guideline-concordant DBP was 7.14 mmHg higher than the mean usual-care DBP (p ≤ 0.001) (
Comparison of means of blood pressure (systolic and diastolic) between guideline-concordant and usual-care blood pressure measurement protocols using the paired
Variable | Category | Mean ± SD | Sig. | |
---|---|---|---|---|
Systolic BP | Guideline-concordant | 130.89 ± 24.97 | 7.31 | < 0.001 |
Usual-care | 123.22 ± 25.06 | - | - | |
Diastolic BP | Guideline-concordant | 81.76 ± 14.92 | 7.83 | < 0.001 |
Usual-care | 74.62 ± 14.22 | - | - |
SD, standard deviation; BP, blood pressure. Sig., significance.
The proportion of participants classified as having hypertension among respondents who were not previously hypertensive was 11.8% lower when using usual-care BP compared to guideline-concordant BP (16.8% vs. 28.6%). The proportion of participants classified as having uncontrolled BP among respondents who previously had hypertension was 15% lower when using usual-care BP compared to guideline-concordant BP (44.8% vs. 59.8%) (
Pattern of blood pressure among respondents based on usual-care and standard blood pressure measurement protocols.
Blood pressure control based on usual-care BP | Blood pressure control based on guideline-concordant BP | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Respondents who previously had no hypertension | Respondents who previously had hypertension | |||||||||
Normal BP | Hypertension | Total | Controlled BP | Uncontrolled BP | Total | |||||
% | % | % | % | |||||||
82 | 82.8 | 17 | 17.2 | 99 | 27 | 56.3 | 21 | 43.8 | 48 | |
3 | 15.0 | 17 | 85.0 | 20 | 8 | 20.5 | 31 | 79.5 | 39 | |
BP, blood pressure.
Overall, the treatment decisions based on the two protocols were in agreement in 155 (75.2%) of the respondents; hence, 51 (24.8%) respondents had incorrect treatment diagnosis based on usual-care BP measurement. Of the participants who were not supposed to start or have treatment adjustment based on the guideline-concordant measurement protocol, 13 (22.0%) of them would have been wrongly given antihypertensives based on the usual-care BP measurement protocol. Of those who will need to start or change treatment based on the guideline-concordant measurement protocol, 38 (25.9%) of them would have missed the opportunity if the treatment decision was based on the usual-care BP measurement protocol (
Comparison of treatment decisions based on usual-care and guideline-concordant blood pressure measurement protocols.
Treatment plan based on usual-care blood pressure measurement protocol | Treatment plan based on usual-care BP measurement protocol | Total | |||
---|---|---|---|---|---|
No treatment | Treat or change treatment | ||||
% | % | ||||
No treatment | 109 | 74.1 | 38 | 25.9 | 147 |
Treat or change treatment | 13 | 22.0 | 46 | 78.0 | 59 |
BP, blood pressure.
The intra-class coefficient (ICC) of 0.87 (95% CI: 0.77–0.93) was almost perfect for SBP and strong for DBP; ICC = 0.70 (95% CI: 0.48–0.81) for the two BP protocols. The linear regression relationship for SBP and DBP between usual-care (pragmatic) and guideline-concordant (standardised) BP was summarised as SBPPr = 15.68 + 0.82 × SBPSt and DBPPr = 28.06 + 0.57 × DBPSt (
Pearson (
Blood pressure | BP measurement method in comparison | Pearson coefficient, |
Intra-class coefficient ( |
Regression equations for relationship between blood pressure methods |
---|---|---|---|---|
Systolic BP | Guideline-concordant/usual-care | 0.8 | 0.9 | SBPPr = 15.68 + 0.82 × SBPSt |
Diastolic BP | Guideline-concordant/usual-care | 0.6 | 0.8 | DBPPr = 28.06 + 0.57 × DBPSt |
BP, blood pressure; SBPPr, systolic blood pressure pragmatic; SBPSt, systolic blood pressure standardised; DBPPr, diastolic blood pressure pragmatic; DBPSt, diastolic blood pressure standardised.
, Interpretation based on Pearson coefficient (r): −1.0 to −0.7 strong negative association; −0.7 to −0.3 weak negative association; −0.3 to +0.3 little or no association; +0.3 to +0.7 weak positive association; +0.7 to +1.0 strong positive association.
, Interpretation based on intra-class coefficient: Intra-class coefficient can be interpreted as follows: 0.0–0.2 indicates poor agreement: 0.3–0.4 indicates fair agreement; 0.5–0.6 indicates moderate agreement; 0.7–0.8 indicates strong agreement, and > 0.8 indicates almost perfect agreement.
From the Bland-Altman plot, the limits of agreement between the usual-care and standardised BP were between −21.85 mmHg and 37.19 mmHg for SBP and −18.51 mmHg and 32.78 mmHg for DBP. The two methods could not be used interchangeably because the pre-defined maximum allowed difference of 10 mmHg was smaller than the higher limits of agreement and higher than the lower limits of agreement (
The Bland-Altman plot difference against the mean for (a) diastolic blood pressure and (b) systolic blood pressure – guideline-concordant compared to usual-care.
The study showed that the left arm was used for the single BP measurement in about two-thirds of the participants in the usual-care protocol. Anecdotal evidence from the regular clinic nurses that measured the usual-care BP showed that the BP measurement on the left arm is more reliable because of its closeness to the heart. This may not always be true as seen in the index study where the SBP and DBP readings on the right arm were higher than those of the left arm in the majority of the participants. The preferred choice of the left arm for BP measurement by the nurse in the usual-care protocol contradicts the recommendation of various guidelines on BP measurement which state that the arm with higher reading should be used for measuring the BP.
Our study showed that the mean SBP and DBP values measured using the usual-care measurement protocol were lower compared with the those using the guideline-concordant measurement protocol. The reason for the lower usual-care BP values in the index study may be attributed to non-adherence to BP measurement guidelines. For instance, the usual-care BP measurement protocol that was solely based on the readings from one arm, in most cases the left arm in the index study, may lead to lower usual-care BP values because of the evidence in favour of higher BP on the right arm when using the guideline-concordant protocol in the majority of the participants.
Similar to this study, a previous Canadian study that compared casual in-clinic BP measurements to standardised BP measurements among severely obese patients in a bariatric clinic also found that casual in-clinic BP measurements were, on average, lower than standardised measurements.
Unlike the index study and the Canadian study, the previous studies on this topic, however, reported contrary conclusions; that is, usual-care BP measurements were higher than standardised measurements.
Ideally, higher readings in the usual-care BP will be expected because most of the reasons for inaccurate BP measurement that are common with usual clinic BP measurement result in falsely elevated readings. The potential bias would be more in the Canadian study where severely obese patients were used because of the recognised concerns related to arm circumference, length and shape which can predispose to falsely elevated readings.
The potential explanation for the observed difference in findings between the index study or Canadian study and previous studies
The implications of the significant variation between usual-care and guideline-concordant BP on diagnosis was obvious in the index study. Our study showed that the usual-care BP measurements underestimated BP, reducing the diagnosis of uncontrolled hypertension by 15% in previously hypertensive patients and hypertension by 11.8% in previously normotensive patients. This observation was similar to many studies that showed misdiagnosis of hypertension if BP was not measured according to guidelines.
The misdiagnosis based on usual-care BP measurement in this study affected the treatment decision. About one out of every four (24.8%) participants in the study had an incorrect treatment diagnosis. Majority of the participants who had incorrect treatment decision would have missed the opportunity of being treated or get exposed to unnecessary adverse effects of these drugs based on usual-care BP. It is obvious that the improvement in BP measurement techniques might result in the prevention of needless mortality and treatment burden.
This study showed that the use of the correlation coefficient to see whether usual-care protocol agrees with the guideline-concordant protocol for BP measurement was misleading. Despite the strong correlation coefficient, the Bland-Altman plot showed that the two protocols did not agree. This lack of agreement is by no means obvious from our findings with the limits of agreement being wider than the within 10 mmHg clinical reference range. The difference is enough to even affect decisions on patients’ management even if the reference ranges for hypertension severity grading using JNC 7 guideline-based value of 20 mmHg for SBP and 10 mmHg for DBP were used.
The use of ambulatory and automated measurement of BP in clinical practice and research is likely to eliminate this disparity and its consequences because of reliability and consistency of diagnosis of hypertension.
This study showed that the usual-care BP readings varied significantly from the guideline-concordant BP readings. Furthermore, we unexpectedly found that the usual-care BP protocol might underestimate the BP readings obtained from the guideline-concordant protocol. The incongruence between usual-care BP readings and guideline-concordant BP readings could result in an incorrect diagnosis and inappropriate treatment. The training of primary health care workers who are involved in BP measurements will improve the level of adherence to BP measurement guidelines and eliminate incorrect BP measurement and its consequences.
The regular clinic nurses who measured the usual-care BP may not accurately represent how other health workers will adhere to BP measurement guidelines. In addition, the BP measurements may be elevated in the presence of health care professionals – the white coat effect. However, the measurement of BP by nurses using both usual-care and guideline-concordant protocols makes it negligible because the white coat effect appears to be greater for doctors than for nurses.
The authors have declared that no competing interests exist.
All authors contributed equally to this work.
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sector.
Data sharing is not applicable to this article as no new data were created or analysed in this study.
The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of any affiliated agency of the authors.
Dear Sir/Ma,
I hereby seek your consent to participate in this research.
I am a doctor at the Department of Family Medicine, Federal Medical Centre, Abeokuta. I intend to find out the variation between usual-care blood pressure measurement and guideline-concordant blood pressure measurement among patients seen at a family practice clinic of the Federal Medical Centre, Abeokuta- Implications for subsequent management.
If you consent, a questionnaire will be administered on you followed by a physical examination. The procedure will last for about 30 minutes. The result of this project will be published in a journal.
Your participation is entirely of your own free will and you can withdraw from the study at any time you like without explanation. Refusal to participate in the study will not affect your treatment in anyway. You have the right to refuse to answer any question you don’t want to answer.
Please note that any information collected will remain confidential. Your name will not be attached to any published results. Kindly indicate your decision by signing in the space below.
Thank you.
Date and signature or thumb print of witness Date and signature or thumbprint of participant
Good day Sir/Ma,
Thank you for consenting to participate in this study. This research is about finding out the variation between usual-care and guideline-concordant blood pressure measurements. It will help us serve you better. Your cooperation is needed to truthfully answer the questions below. All information will be strictly confidential and it will take only a few minutes. Thank you.
Serial Number …………………………………..
Hospital number ………………………………..
Date …………………………………………………
Male Female Single Married Divorced Separated Widowed Islam Christianity Traditional belief Others Yoruba Hausa Igbo Others No formal education Primary Secondary Tertiary
Right arm Left arm Both arm Yes No
BP
Usual-care
Guideline-concordant
Difference
SBP
Right arm
Left arm
DBP
Right arm
Left arm
Guideline-concordant
Usual-care
Normal
Controlled
Uncontrolled
Hypertension
Treatment decision
No treatment
Treat
Change treatment
Based on usual-care BP
Based on guideline-concordant BP
Classification
Yes
No
Wrongly treated with anti-hypertensives based on usual-care BP measurement only
Missed the opportunities of being treated based on usual-care BP