Q: What is "normal" blood pressure (BP)? Is it different from optimal BP?
A: This question is frequently raised by both clinicians and patients, particularly in view of the changing definitions of hypertension in the last several reports of the Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC V, JNC VI, and JNC 7).1-3
For many years, a reading of 140/90 mm Hg served as the dividing line between normal and high BP and was used by many life insurance companies to determine the risk associated with hypertension. Observational studies have since demonstrated that the risk of cardiovascular disease (CVD) begins at BP levels as low as 115/75 mm Hg and doubles with each increment of 20/10 mm Hg. Prospective studies have repeatedly identified an increasing risk of CVD, stroke, and renal insufficiency at progressively higher levels of both systolic and diastolic BP. Furthermore, a positive, continuous, and independent association has been observed between BP and the incidence of CVD, stroke, heart failure, and end-stage renal disease.
As a result, the JNC V and JNC VI guidelines designated optimal BP as 120/80 mm Hg or lower, and normal BP as less than 130/80 mm Hg. They also included a high-normal BP category, which was defined as 130 to 139/85 to 90 mm Hg.
The newest classification. With the recognition of the consistent relationship between BP and the risk of CVD, independent of other risk factors, the authors of JNC 7 introduced a new classification of hypertension. The category of "prehypertension"—systolic BP of 120 to 139 mm Hg or diastolic BP of 80 to 89 mm Hg—was added to acknowledge the risk relationship across the entire BP range from 115/75 to 185/115 mm Hg. This new category signals the need for increased education of health care professionals and the public in order to reduce BP levels and prevent progression to sustained hypertension.
Normal BP is now considered to be below 120/80 and is synonymous with the previous designation of "optimal BP." Patients with sustained BP higher than 140/90 mm Hg are considered to have hypertension and are candidates for aggressive pharmacological therapy.
Management of prehypertension. Management is currently directed toward aggressive lifestyle modification, because at the time of publication of JNC 7, there were no prospective clinical trials that demonstrated reduced cardiovascular risk as a result of either lifestyle or drug treatment of prehypertension. Subsequently, a small prospective trial demonstrated that progression to sustained hypertension could be prevented during 2 years of pharmacologicaltreatment in patients with BPs of 130 to 139/85 to 89 mm Hg (which was considered high-normal BP at the time that the study was planned).4 Firm evidence from large prospective trials will be required before aggressive pharmacological therapy can be recommended for the more than 70 million persons who meet the current criteria for prehypertension.
Implications for your practice. I would be remiss if I did not remind clinicians that the diagnosis of hypertension should not be made on the basis of a single BP reading, unless that reading is extremely high or the patient has shown evidence of progressive target organ disease. Rather, a series of BP readings during a period of several weeks is appropriate; this should include out-of-office readings, which can now be obtained using a variety of automated and portable BP devices. The choice of antihypertensive agents and the aggressiveness of therapy will also relate, in part, to the presence of additional cardiovascular risk factors, such as hyperlipidemia, diabetes, cigarette smoking, sedentary lifestyle, and a family history of premature myocardial infarction or stroke.
Finally, JNC 7 has drawn its share of criticism relative to both its revised classification and its treatment recommendations. However, I encourage you to continue to use these recommendations pending future developments. Such developments may include classification and treatment recommendations based on global cardiovascular risk and guidelines that take into account all of the cardiovascular risk factors in a patient with new-onset hypertension.