1. Blood pressure measurement in primary care
Frank Lefevre MD
Associate Professor of Medicine
Division of General Internal Medicine,
Northwestern Feinberg School of Medicine

2. Rationale
Achieving optimal outcomes in the treatment of HTN requires accurate BP assessment
Current practice patterns for measuring BP are suboptimal

3. Overview How accurate are various methods of BP measurement?
Office BP measurement
Out of office BP measurement
Patient self-measurement
Ambulatory BP monitoring
Can the use of out of office BP measurements improve outcomes?
Diagnosing HTN
Monitoring treatment
How can BP measurement be improved?

4. Sources of error in BP measurement
Measurement error
Random variability
White coat effect

5. Standardized BP measurement (AHA guidelines, Circulation, 1993;88:2460)
Patient should be:
seated in relaxed environment for 5min
Legs resting on floor
Back supported
No conversation
Bare arm supported on table, midpoint of upper arm at level of heart
Examiner technique:
Place cuff 1-2cm above antecubital fossa,
Inflate cuff, palpate to estimate SBP
Place bell of stethoscope over brachial artery, do not wedge under cuff
Inflate cuff 20-30mm above estimated SBP
Deflate at 2mm/sec, listen for Karatkov sounds
Allow subject to rest for at least 30sec
Repeat measurement and take average of both measurements

6. Do MD’s follow standardized approach
Do MD’s follow standardized approach? (McKay et al, J Hum Hyper, 1990;4:639)
Observation of 114 primary care physicians
Assessed potential for measurement error
Accuracy of sphygmomanometers
40% off by  4mm; 30% off by 10mm
Physician technique

7. Impact of errors in technique (McAlister et al, BMJ, 2001;322:908)
Factor
Systolic BP
Diastolic BP
Talking
 17mm Hg
 13mm Hg
Exposure to cold
 11mm Hg
 8mm Hg
Ingestion of alcohol
Supine
No effect
 2-5mm Hg
Arm position above heart
 8mm Hg/10cm
Arm position below heart
 8mm Hg/10cm
Arm not supported
 2mm Hg
Cuff too small
 3 mm Hg

8. Effect of random variability on the diagnosis of HTN (Mar et al, J Med Dec Mak, 1998)
Modeling study
Simulated predictive value of diagnosing mild HTN with 3 measurements (office BP measure), as compared to 24 measurements (ambulatory BP measure), accounting for random variability
Did not consider white coat effect or measurement error
PPV
3 BP measurements:
24 BP measurements:

9. The “white coat effect” (WCE)
Generally defined as: (office BP - out of office BP)
Alerting response causing acutely elevated BP
May be large; up to 40% of pts have WCE > 20/10mm Hg
Magnitude dependent on number of office readings
Larger magnitude:
Taken by physician
Older patients
Higher baseline pressure

10. Difference in SBP readings between clinic BP and ABPM

11. Comparative accuracy of different methods of BP measurement
Lack of true gold standard
Accuracy estimated by:
Predictive ability for future CV events (prospective studies)
degree of correlation with hypertensive end-organ damage (cross-sectional studies)

12. Prospective cohort studies (Perloff et al 1989:
1,079 patients with essential HTN followed for 5.5 years.
Classified patients as ABP higher than predicted by office BP, same, or lower than predicted:
Patients with ABP lower than predicted had more favorable prognosis
Major limitations:
Did not specifically evaluate patients with WC HTN
Confounding by treatment of patients with “WC HTN”
Failed to consider covariates contributing to cardiac events

13. Prospective cohort studies (Verdecchia et al 1989)
1,187 patients with essential HTN followed for mean of 3.2 years.
WC HTN defined as office BP >140/90 and ABP<136/87 (men) or 131/86 (women); n=228.
Compared with 205 healthy normotensive patients
ACE/100 pt-yrs
True HTN:
WC HTN:
Normotensive:
Major limitation - confounding by treatment in WC HTN group.

14. Prospective cohort studies (Khattar 1998)
: Longest cohort study:
479 patients followed for over 9 years from one center in UK; 126 patients with WC HTN
rate of adverse cardiovascular events for WC HTN compared with sustained HTN
ACE’s/100 pt-yrs
WC HTN
Sustained HTN
Major limitations:
no comparison with normotensive group
confounding by treatment (82% WC pts treated)

15. Cross-sectional studies
Numerous studies comparing accuracy of ABP and office BP by comparing correlation with end-organ damage (LVM)
Meta-analysis of 21 studies (Fagard et al 1995):
Correlation with LVM
Ambulatory BP: r = 0.50
Office BP: r = 0.35

16. Ambulatory BP monitoring – de facto gold standard?

17. Limitations of ABP monitoring
No good epidemiologic benchmarks for determining treatment threshold
Virtually all studies of treatment and prognosis have used office BP readings
One epidemiologic study of ABP/prognosis (Okhubo et al 1998):
Population based study of ABP and prognosis
1542 patients from one city in Japan followed for 6.2 years
Ambulatory BP associated with best prognosis:
mmHg systolic
65-78mmHg diastolic

18. Interpretation of ABPM results (Adapted from Okhubo et al, Hyperten, 1998;32:255)
Probably normal
Borderline
Probably abnormal
Mean SBP
Awake
<135
>140
Asleep
<120
>125
24 hour
<130
>135
Mean DBP
<85
85-90
>90
<75
75-80
>80
<80
80-85
>85

19. Patient self-monitoring
Accuracy approaches that of ABPM in groups of patients in research studies
Accuracy/validity of measurements in individual patient less certain
Validity may vary by whether used for diagnosis of HTN vs management of known HTN

20. Comparison of office, home and ambulatory BP’s
Study N
Mean Systolic BP
Office Self ABP monitor
Kleinert 1984 93
148
138
131
Flapan 1987 24
167
151
126
Kenny 1987 19
156
147
139
Marolf 1987 31
134
130
Bialy 1988 15
129
James 1988 13
155
141
133
O’brien 1988 18
160
153
Mengden 1992 51
149
Mancia 1995
1438
128
119
118
Weighted Avg
1702
131.6
122.5
120.7

21. Difference between clinic and self- measured blood pressure (Adapted from

22. Difference between ABPM and self- measurement of BP (Adapted from

23. How often do individual patients get inaccurate self-readings
How often do individual patients get inaccurate self-readings? (Merrick et al, South Med J, 1997;90:1110
Methods:
91 volunteer patients self-measured BP in the presence of trained technician
Accuracy defined as systolic and diastolic BP within 10mm of values recorded by technician
Results:
66% accurate
34% inacurrate
Clinical and demographic factors not predictive of accuracy

24. Performance characteristics for SBP measurement in diagnosing HTN (Little et al, BMJ, 2002;325:254)
Sensitivity (%)
Specificity (%)
LR +
LR -
Doctor
91.2
25.8
1.2
0.33
Nurse
83.3
41.2
1.4
0.41
Self – Hospital
92.7
50.0
1.9
0.15
Self- Home
87.0
59.7
2.2
0.22

25. RCT’s comparing ABPM with office BP for monitoring HTN

26. Outcomes of monitoring BP with ABPM vs office measurement Staessen et al
419 patients with office DBP >95 randomized to follow-up with either ABPM or office BP
Medication adjusted in a stepwise fashion according to BP measurements

27. Improving BP measurement
“HTN clinic” approach
“Out of office” approach
“Individualized” approach

28. Improving BP measurement
“HTN clinic” approach
Dedicated personnel
Specific training in HTN
Standardized BP measurement
Patient education

29. Improving BP measurement
“Out of office” approach
Use out of office measurements to guide decision-making
Use self-measurement in patients with demonstrated accuracy
Use ABPM in others, or when validity is uncertain

30. Improving BP measurement
Individualized approach in managing BP
Assess absolute risk for ACE’s
Treat based on expected benefit
Absolute risk may vary markedly at any level of BP
Expected benefit closely related to absolute risk
RRR of treatment will be same regardless of whether BP measure is precise

31. Conclusions
Measurement of BP in the primary care office is highly prone to error
Out of office BP measurements can be more accurate than office BP’s
Lack of strong evidence demonstrating an improvement in outcomes associated with OOO-BP readings
Multiple potential areas for improvement in BP assessment