In this national survey, 49% and 52% of the participants with hypertension who did not have CKD had uncontrolled BP by the general and disease-specific guidelines, respectively. Uncontrolled BP was more prevalent in the CKD population, with 52% and 69%, respectively, having uncontrolled BP by the general and disease-specific guidelines. These estimates were not substantially lower than the rates of uncontrolled BP (62–70%) reported in CKD stage 5 patients treated with hemodialysis (24
The substantially higher prevalence of uncontrolled BP in those with CKD relative to those without CKD are likely due to difficulties associated with controlling BP in those with CKD. The JNC-7 guidelines (1
) recommend that patients with CKD, the vast majority of whom have hypertension, receive aggressive management, including the use of three or more medications at increasing doses; in fact, consensus evidence shows that an average of more than three medications are needed to control BP in CKD (26
). We found that one-third of those with CKD and hypertension were not treated with medications; of those on treatment, only 37% and 28% of those with CKD and hypertension were on ACE inhibitors/ARBs and diuretics, respectively. Moreover, despite their association with a lower likelihood of uncontrolled BP, only 22% of those with CKD and uncontrolled blood pressure were on ACE inhibitors/ARBs. Similarly, after adjustment, only 23% were on multiple medications. This is despite our findings that uncontrolled BP rates in CKD were lowest in those on two or more agents, but only after adjustment for factors contributing to the indication for treatment (i.e.
, factors associated with poor control requiring multiple medications). Although this study was not conducted in a healthcare setting, these results suggest that there may be an educational deficit in the community with regard to optimal care of hypertension.
Both patient and provider factors could play a role in the lack of BP control among those with CKD. Patient factors that may impede BP control in those with CKD include the lack of a primary care provider or non-adherence to medications and dietary guidelines. Non-adherence may result from a lack of understanding of the importance of BP for preventing progression and complications of CKD; cognitive difficulties associated with CKD (27
); fear or intolerance of medication side effects; and the cost of medications, especially multiple medications. Hypervolemia and/or increased arterial stiffness, suggested by the substantially higher pulse pressure we found in those with CKD, may also make BP control very difficult among these patients, even with primary care and adherence.
The provider’s role in controlling BP in CKD involves both recognizing CKD and knowing and adhering to CKD-specific guidelines. Previous surveys have shown that primary care physicians may be unlikely to recognize some risk factors (28
) and may only recognize CKD upon testing at rates of 59–78% (29
). A 2007 survey (30
) showed that physicians in training (internal medicine residents) selected a BP target of 130/80 or less for patients with CKD nearly 90% of the time, and 98% identified ACE inhibitors/ARBs as part of the treatment plan, indicating that knowledge of CKD guidelines may be improving.
We also found evidence that uncontrolled BP decreased in both those without and with CKD from 1999–2002 to 2003–2006, coincident with the release of new hypertension guidelines in 2003 (1
). This may be due to greater physician knowledge of and adherence to the revised guidelines or to a greater availability of multiple medications for aggressive treatment of BP in CKD. In fact, ACE inhibitors/ARBs were used more frequently in more recent survey years. However, despite this evidence of a downward trend in uncontrolled BP, control remains poor, by any definition, in both the non-CKD and CKD populations.
We also found that BP control was often associated with demographic characteristics. As with previous studies (6
), we found that older age (usually associated with arterial stiffness) was strongly associated with uncontrolled BP in those with and without CKD, regardless of the definition used. Although a previous study using the NHANES population-based survey data showed an increased risk of uncontrolled BP in males in the general population (5
), a more recent study by Ostchega et al. (6
) showed that females were more likely to have uncontrolled BP. We found that females with CKD were at greater risk for uncontrolled BP, in agreement with a previous study of volunteers with CKD (32
), but only using the general definition. Non-whites with CKD were at greater risk for uncontrolled BP, which has been shown previously (5
), possibly due to greater medication nonadherence and worry about hypertension (33
Socioeconomic factors, including higher level of education, insured status, and high income, were not associated with risk of uncontrolled BP after adjustment for demographics and clinical characteristics, suggesting that physiologic factors dominate socioeconomic influence on BP control in the CKD population. This finding highlights the necessity of better professional and broad-based patient education in efforts to improve BP control. As expected, diabetes (34
) was associated with uncontrolled BP in the non-CKD population but not in those with CKD. This is likely a reflection of the physiological mechanisms (e.g.
, salt and water retention due to reduced kidney function, aldosterone excess, or sympathetic overactivity) that lead to hypertension once CKD develops, regardless of the underlying causes of the disease. Interestingly, regardless of CKD status (i.e.
, kidney function), presence of albuminuria was strongly associated with increased prevalence of uncontrolled blood pressure, as has been reported previously in CKD populations (8
There are some limitations of the study that deserve mention. First, although we chose to examine CKD stage 3 and 4 only to minimize the error associated with single albuminuria measurements, we almost certainly have some misclassification of CKD stage 1 and 2 as “non-CKD,” which may have attenuated some of our comparisons between the two populations. However, because these early stages are currently neither well-recognized nor universally accepted (36
), we believe that many of these participants are likely to be treated as “non-CKD” in the treatment of their hypertension. Second, information on treatment nonadherence, which may be differential by either CKD status or other patient characteristics (such as age or race), was not available. Additionally, we did not have enough observations to examine various combinations of medications as predictors of uncontrolled BP. Third, as with any observational study, there may be unknown or unmeasured factors that affect BP control for which we could not account. For example, psychosocial reasons such as hopelessness, frustration with treatment, and anxiety, have been proposed as predisposing factors for poor BP control (37
). Fourth, although the method of blood pressure measurement (office BP at a single point in time) in NHANES was the only practical means of assessing BP in a large national survey, it may not have captured all the uncontrolled BP in the population, particularly in those with CKD whose BP may be elevated outside the clinic setting (e.g.
, at home or during routine daily activities) and could be captured with ambulatory BP monitoring. A recent study (38
) found that white-coat hypertension and masked hypertension, particularly, were prevalent among those with CKD; this phenomenon may have further attenuated the differences between participants with and without that we observed here. Finally, changes in therapy or other patient characteristics cannot be assessed over time in a cross-sectional survey. Additionally, provider knowledge of BP control guidelines in CKD and the general population and quality of patient-provider communication may play a significant role in BP control and could not be ascertained here.