Previous population-based studies have reported high rates of hypertension in patients with moderate CKD. In the current study of patients with CKD primarily identified by healthcare providers and through clinical databases, 85.7% of participants had hypertension. In contrast to previous reports of low rates of hypertension awareness and treatment among adults with CKD, these rates exceeded 98% in the CRIC study. Furthermore, in the context of almost universal hypertension awareness and treatment, hypertension control rates were higher than in several previous reports of adults with CKD. However, hypertension control rates were still far from optimal; 67.1% and 46.1% of CRIC participants had their hypertension controlled to systolic and diastolic blood pressure levels <140/90 mmHg and <130/80 mmHg, respectively.
Recruiting CKD patients from clinic settings resulted in a population that is different from those previously used to study hypertension control among individuals with CKD in previous observational studies. For example, the prevalence of hypertension was 71% among Framingham Offspring Study participants with CKD5
. While 86% of these participants were treated, only 37% controlled their hypertension to systolic and diastolic blood pressure <140/90 mmHg, respectively. Furthermore, hypertension control to <130/80 mmHg was only 27%. Factors associated with hypertension control were not evaluated in the Framingham cohort with CKD. In NHANES III, Coresh reported only 27% of individuals with elevated serum creatinine had a systolic/diastolic blood pressure < 140/90 mmHg4
. Further, only 75% of those with hypertension were taking antihypertensive medication. Peralta and colleagues evaluated hypertension control to <130/80 mmHg among individual with CKD, eGFR < 60 ml/min/1.73m2
or albuminuria, in the 1999-2002 National Health and Nutrition Examination Survey and only 56% and 37% had controlled their blood pressure to <140/90 and <130/80 mmHg, respectively8
A recent analysis of the National Kidney Foundation’s Kidney Early Evaluation Program (KEEP), a screening program aimed at identifying patients with CKD, was conducted to assess rates of hypertension awareness, treatment and control7
. Among patients with stage 3 CKD, defined as an eGFR between 30 and 59 ml/min/1.73m2
, 81.9% of patients with hypertension were aware of this diagnosis and 72.7% were receiving pharmacological treatment. Despite these relatively high awareness and treatment rates, hypertension control rates were substantially lower than in the current study; only 20.3% of KEEP participants with stage 3 CKD had their systolic and diastolic blood pressure controlled to <140/90 mmHg. A major difference between KEEP and the CRIC study is that only 6.5% of KEEP participants were aware of their CKD. The substantially higher rate of hypertension control in the CRIC study is noteworthy. It suggests that clinical feedback may play a key role in achieving hypertension control.
Consistent with the current study, non-Hispanic blacks in KEEP were less likely to have controlled their hypertension. In contrast, male gender and lower BMI were associated with hypertension control in the KEEP study but not in the CRIC study. However, the factors associated with hypertension control in the KEEP study may be confounded by low antihypertensive treatment rates. Reasons for the sub-optimal rates of hypertension control among patients with CKD prescribed antihypertensive medications warrant further investigation.
The lack of an association between several factors studied and hypertension control warrants discussion. For example, in contrast to previous studies, overweight and obesity and cigarette smoking were not associated with hypertension control. It is possible that previous studies may have been confounded by differential access to healthcare. Supporting this assertion, over 98% of CRIC participants had their blood pressure checked within the year prior to their study visit. In a previous study of the general US population, adults with hypertension who had their blood pressure checked in the prior year were five times more likely to have controlled hypertension11
. Hypertension control rates were similar also for CRIC participants who had and had not seen in a nephrologist previously.
Diabetes was associated with lower hypertension control rates in a multivariable adjusted regression model that did not include albuminuria. However, this association was no longer present after adjustment for albuminuria levels. Albuminuria levels are higher among individuals with diabetes and may indicate the need for more aggressive treatment. An additional unexpected result was the lack of an association between eGFR and hypertension control. This may have resulted from more aggressive treatment among CRIC participants with lower eGFR. Specifically, 42.1% of CRIC participants with an eGFR < 30 ml/min/1.73m2
were taking 4 or more classes of antihypertensive medications, compared to 39.2%, 27.4%, 26.0%, and 18.6% for those with an eGFR of 30-39, 40-49, 50-59 and ≥ 60 ml/min/1.73m2
, respectively. However, no association was present between higher serum creatinine and lower hypertension control rates in a prior analysis of NHANES 1999-20028
Clinical trials have demonstrated that weight loss, sodium reduction, exercise, and alcohol restriction reduce blood pressure among adults with hypertension12-15
. In a previous study of the general population, adults using these lifestyle changes were six times more likely to have controlled hypertension11
. The lack of an association between lifestyle modifications and hypertension control in the current study should not be inferred to mean that these interventions are not beneficial. The higher rates of hypertension control in the current study compared to previous studies may be due to the high utilization of lifestyle modifications. Nonetheless, the lack of association with hypertension control for lifestyle modifications warrants further investigation into the quantity and quality of lifestyle modifications being performed among patients with CKD.
Findings from the current analysis must be considered within the context of its limitations. Most notably, data were derived from a single study visit. However, the rates of hypertension prevalence, awareness, treatment and control were markedly similar when blood pressure measurements from the CRIC screening and baseline visits were used to define hypertension. The CRIC study is observational. Therefore, as mentioned previously, caution should be taken when considering the association between the number and classes of antihypertensive medication taken and lifestyle changes and hypertension control. Also, the assessment of lifestyle changes were based on single questions and measurement error for this domain is possible. Finally, the CRIC study population was identified mostly through physicians and clinical databases. Therefore, the results are not representative of all patients with moderate CKD. However, the current study provides data on hypertension awareness, treatment and control in the context of patients with CKD in the clinical environment, an area with few published data available.
The current analysis maintains several strengths including the large population of patients with CKD enrolled in the CRIC study and collection of an extensive array of demographic, socio-economic, behavioral, and medical-related factors. Such extensive data collection permitted conduct of a comprehensive analysis of factors associated with hypertension control in patients with CKD. Additional strengths include the use of a standardized protocol with stringent quality control procedures for measurement of blood pressure. Finally, the current study included a diverse population with respect to degree of renal insufficiency.
Hypertension is a common co-morbidity affecting the vast majority of patients with CKD. Given the high risk of CVD and CKD progression associated with hypertension, its control may have important benefits for patients with CKD. Despite almost ubiquitous awareness and antihypertensive treatment rates in the current study, fewer than 50% of CRIC participants achieved the target blood pressure of systolic/diastolic blood pressure < 130/80 mmHg. Increased efforts are needed to identify the reasons for inadequate hypertension control and approaches to increase blood pressure control among patients with CKD.