High BP is the major manifestation of hypertension, a disease of the vasculature.
Deemed a pandemic by some, the prevalence of hypertension was approximately 26.4% in 2000 and has been projected to increase to 29.2%, or approximately 1.56 billion people, by the year 2025 (JAMA. 2003;289:2363-2369. One estimate by Cene and colleagues notes that hypertension is responsible for 12.8% of all deaths.
High BP is a key pathogenic factor that contributes to the deterioration of kidney function, but the kidney itself can also be responsible for elevations in BP. Note that presence of stage 3 or higher nephropathy is a common and underappreciated pre-existing medical cause of resistant hypertension.
Current guideline recommendations mandate a BP goal of 130/80 mm Hg or lower for patients with advanced proteinuric nephropathy to maximally slow progression of their kidney disease. In recent reviews of National Health and Nutrition Examination Survey (NHANES) data from 1999-2006, this goal was achieved in fewer than 25% of patients with stage 3 or higher nephropathy (e.g., Am J Kidney Dis. 2009;53[4 Suppl 4]:S22-S31 and Hypertension. 2009;54:47-56). Therefore, treatment of hypertension is a critically important intervention in the management of all forms of CKD.
BP increases above the level of 115/75 mm Hg have a direct and continuous relationship on cardiovascular morbidity. For every 20/10 mm Hg rise in BP above 115/75 cardiovascular risk doubles, according to The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7).
Moreover, global studies have demonstrated that geographic areas with a high prevalence of hypertension also show elevations in myocardial and intracranial ischemia (Lancet. 2005;365:217-223) and subsequent increases in the incidence of cerebral hemorrhage, heart failure, and CKD.
Between 1976 and 1980, the nationwide prevalence of hypertension was about 43%, but by the early 1990s, that number had dropped 40%. However, data from the most recent NHANES survey (2006) show increases in hypertension rates among those with CKD. In 2005-2006, the prevalence of hypertension (defined as BP greater than 140/90) in U.S. adults was 29%.
The rates of hypertension were highest in individuals aged 60 years or older (67%) and in non-Hispanic blacks (41%), compared with whites (28%) or Mexican Americans (22%). Furthermore, hypertension was more common in persons with a higher BMI (52% for BMI greater than 30 vs. 31% for BMI less than or equal to 30). From 1999 to 2004, 78% of adults with hypertension were aware of their disease, 68% were treated for their hypertension with medications, and fewer than two thirds were controlled to BP below 140/90 with medication, according to a Steering Committee report for World Kidney Day 2009 (Am J Nephrol. 2009;30:95-98).
Note that in the years 1988 through 2002, CKD rates in the NHANES population increased. In a more recent analysis, which took into account the 1999-2006 NHANES data, those with diabetes and hypertension had a far greater prevalence of CKD (37% and 26%, respectively) than individuals without these conditions (11% and 8%, respectively). In the Steering Committee report, the prevalence or amount of CKD stages 1 to 4 in the general population increased 30% from 1988-1994 to 1999-2004.
These differences in CKD burden and hypertension among certain racial and ethnic groups translate into high CKD and cardiovascular mortality rates. The 30-year population mortality risk attributed to hypertension in African-American men and women was twice that of Caucasian men and women (Semin Nephrol. 2005;25:194-197).
An estimated 45% of the medical deaths among African-American men would be prevented by treatment of high BP to less than 140/90 (including losses to stroke and CKD). Compared with whites, blacks develop hypertension earlier in life and have higher average BPs. As a result, there is a greater prevalence of the end-organ effects of hypertension in the black community, where the rates of kidney disease are four times that seen in the general population, as reported in JNC 7.
The geographical distribution of hypertension in the United States is higher in areas where the population is poor, minority, or medically underserved. Prevalence rates in specific areas, e.g., the southeastern United States, known as the “stroke or hypertension belt,” are exceptionally high for those born in the region as well as those who migrated into the area as adults.
The increases seen in hypertension prevalence have been attributed by some to a change in definition to include those being treated and controlled with antihypertensive medications. This suggestion does not take into account, however, individuals with “pre-hypertension” who have a one- to twofold higher cardiovascular mortality risk over time and can progress to stage 3 CKD.