Is Ambulatory BP Monitoring Needed for the Accurate Diagnosis of High BP?

Abstract & Commentary

By Harold L. Karpman, MD, FACC, FACP, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman serves on the speakers bureau for Forest Laboratories.

Synopsis: The use of ambulatory blood pressure (BP)monitoring as a diagnostic strategy for the diagnosis of hypertension after finding an initial raised BP reading in the doctor's office would reduce misdiagnosis. The additional costs of ambulatory monitoring are counterbalanced by cost savings from better targeted therapy and, therefore, ambulatory monitoring is recommended for most patients before the start of antihypertensive drug therapy.

Source: Lovibond K, et al. Cost-effectiveness of options for the diagnosis of high blood pressure in primary care: A modelling study. Lancet 2011;378:1219-1230.

Hypertension is well known as one of the key risk factors for the development of cardiovascular disease,1 is a major cause of morbidity and mortality worldwide,2 and is the most common reason for a primary care referral for consultation among all of the chronic disorders since as many as 25% of adults are hypertensive.3,4 The diagnosis of hypertension has traditionally been based on the results of one or several BP measurements taken in a physician's office, despite the fact that there are great variations in measurement techniques and the inability to accurately control multiple factors, such as transient anxiety, which may contribute to so-called "white-coat" hypertension.5-7 Previous studies have demonstrated that ambulatory BP monitoring (ABPM) is more accurate than clinic and home monitoring8 and have concluded that it should be more frequently utilized.

Lovibond and her colleagues developed a model to assess and compare the cost effectiveness of the three different diagnostic methods (i.e., additional BP measurements in the office, home BP monitoring, ABPM) which are routinely used to evaluate an elevated office BP.9 They performed a Markov model-based probabilistic cost-effective analysis on a hypothetical primary care population aged 40 years or older who demonstrated a BP measurement greater than 140/90 mmHg and a risk factor prevalence equivalent to the general population. They expressed their findings in terms of costs, quality-adjusted life years, and incremental costs for a quality-adjusted life year gained. Their analysis included the cost of diagnosis, antihypertensive therapy, and the management of associated cardiovascular disease. They concluded that ABPM was more cost-effective when compared with additional office monitoring or home monitoring for confirming the diagnosis of high BP (HBP) in patients with suspected HBP based on a BP measurement of 140/90 mmHg or greater obtained on an initial office or clinic BP measurement.

Commentary

ABPM results are known to vary during 24-48 hour measurement periods, but these variations are less than the variations for home BP monitoring; also, ABPM has been demonstrated to be a better predictor of clinical outcomes than home or office BP measurements.11 The Lovibond study concluded that ABPM was the most clinically effective, as well as the most cost-effective, diagnostic strategy for confirming the diagnosis of HBP across a range of eight subgroups in both men and women.9 The study results further concluded that ABPM should be seriously considered for all patients with newly diagnosed hypertension before starting antihypertensive therapy since an accurate diagnosis of true HBP is necessary to determine which patients should receive appropriate drug therapy and which patients should not be treated but simply followed. The relative additional expense of performing ABPM also was demonstrated to be counterbalanced by the cost savings from the better targeting of treatment.

Cost-effectiveness is an increasingly important consideration in all aspects of medical diagnosis and therapy. The Lovibond study was performed primarily to determine the cost-effectiveness of ABPM but the results of the study also clearly demonstrated the medical effectiveness of ABPM technology in evaluating many of the patients that we see on a daily basis. Hopefully, clinicians will be more diligent in the future in their use of ABPM in patients with newly diagnosed presumptive HBP.

References

1. Lewington S, et al. Age-specific relevance of usual blood pressure to vascular mortality: A meta-analysis of individual data for 1 million adults in 61 prospective studies. Lancet 2002;360:1903-1913.

2. Ezzati M, et al. Selected major risk factors and global and regional burden of disease. Lancet 2002;360:1347-1360.

3. Department of Health. Health survey for England 2003 — Trends. www.dh.gov.uk/en/Publicationsandstatistics/Published Survey/HealthSurveyForEngland/Healthsurveyresults/DH_4098913. Accessed June 11, 2011.

4. Informational Centre for Health and Social Care. The quality and outcomes framework 2006/7. http://www.ic.nhs.uk/statistics-and-data-collections/audits-and-performance/the-quality-and-outcomes-framework/the-quality-and-outcomes-framework-2006-07. Accessed August 8, 2011.

5. Whitworth JA, et al. 2003 World Health Organization (WHO)/International Society of Hypertension (ISH) statement on management of hypertension. J Hypertens 2003;21:1983-1992.

6. Verdechia P. Reference values for ambulatory blood pressure and self measured blood pressure based on prospective outcome data. Blood Press Monit 2001;6: 323-327.

7. Redon J, et al. Prognostic value of ambulatory blood pressure monitoring in refractory hypertension: A prospective study. Hypertension 1998;31:712-718.

8. Hodgkinson J, et al. Relative effectiveness of clinic and home blood pressure monitoring compared with ambulatory blood pressure monitoring and diagnosis of hypertension: Systematic review. BMJ 2011;342:d3621.

9. Lovibond K, et al. Cost-effectiveness of options for the diagnosis of high blood pressure in primary care: A modelling study. Lancet 2011;378:1219-1230.

10. Staessen JA, et al. Predicting cardiovascular risk using conventional versus ambulatory blood pressure in older patients with systolic hypertension. JAMA 1999; 282:539-546.

11. Trazzi S, et al. Reproducibility of noninvasive and intra-arterial blood pressure monitoring: Implications for studies on antihypertensive treatment. J Hypertens 1991;9:115-119.