There were 17,794 NHANES participants from the 1999–2006 surveys who were at least 20 years old, underwent mobile examination center (MEC) examinations (including measurement of serum creatinine and urinary albumin-to-creatinine ratio), provided self-reported information on hypertension, and had measured blood pressures; excluding pregnant individuals and those with estimated glomerular filtration rate (eGFR) <15 ml/min/1.73 m2. Among these participants, 5,832 had diagnosed hypertension, 3,046 had undiagnosed hypertension, 3,719 had pre-hypertension, and 5,197 had normal blood pressure. Participant characteristics by hypertension status are shown in . Mean systolic and diastolic blood pressures were highest in those with undiagnosed hypertension. Females comprised the majority of those with diagnosed hypertension, while males were the majority in pre-hypertension. The proportion of individuals who were Mexican-American was larger in undiagnosed and pre-hypertension than in diagnosed hypertension. High school graduates comprised a greater percentage of participants with pre-hypertension and normal blood pressure than they did diagnosed and undiagnosed hypertension. Those participants whose annual household income (relative to household size) fell in the highest quartile were more likely to have pre-hypertension or normal blood pressure rather than diagnosed or undiagnosed hypertension. The presence of health insurance increased across the diagnostic spectrum of blood pressure, and individuals with health insurance comprised the vast majority of those with diagnosed hypertension. The overwhelming majority of participants in all diagnostic groups reported having a regular site for health care, including 84% of those with undiagnosed hypertension. Those individuals with diagnosed hypertension were the least likely to report current or past cigarette smoking. Obese participants (BMI ≥30 kg/m2) comprised a greater percentage of those with diagnosed hypertension than they did undiagnosed and pre-hypertension. Finally, self-reported diabetes mellitus increased across the diagnostic spectrum of blood pressure, with persons with diabetes comprising 16.7% of those with diagnosed hypertension.
Characteristics of adults age 20 years and older by hypertension status, NHANES 1999–2006.
reveals that the unadjusted prevalence of CKD increases throughout the diagnostic spectrum of blood pressure, with 9.9%, 13.9%, 23.8% and 32.0% having CKD in the normal blood pressure, pre-, undiagnosed and diagnosed hypertension groups, respectively. In the same figure, examination of the stages of CKD revealed that the unadjusted prevalence of CKD stages 3/4 (eGFR 15 to 60 ml/min/1.73m2)was 3.9%, 6.3%, 11.2% and 19.6% for the normal blood pressure, pre-hypertension, undiagnosed and diagnosed hypertension groups, respectively. Notably, a greater proportion of CKD stage 3/4 was found among those with diagnosed hypertension than among the other groups (comprising 61.0% of those with CKD and diagnosed hypertension).
Population prevalence (%) of CKD stages 1–4, by hypertension status, NHANES 1999–2006
shows that even after adjustment for age, race/ethnicity and gender the prevalence of CKD increases throughout blood pressure categories, with 13.4%, 17.3%, 22.0% and 27.5% having CKD in the normal blood pressure, pre-, undiagnosed and diagnosed hypertension groups, respectively. Additionally, persons with either pre- or undiagnosed hypertension accounted for 35.0% of all cases of CKD, while those with diagnosed hypertension accounted for 52.2% of cases (data not shown). These findings suggest that there are as many as 8 million U.S. adults with undiagnosed or pre-hypertension who also have CKD (data not shown).
* Adjusted prevalence of CKD by participant characteristics and hypertension status, NHANES 1999–2006.
Increasing age and female gender were associated with greater prevalence of CKD in all hypertension groups (). Mexican-Americans had the highest adjusted prevalence of CKD (39.8%) among those with diagnosed hypertension, and a similar, but non-significant, trend was present among those with undiagnosed and pre-hypertension. Lack of high school diploma was associated with a greater prevalence of CKD among those with pre-, undiagnosed and diagnosed hypertension; and decreasing household income was associated with greater prevalence of CKD in all blood pressure groups. Obesity was associated with a greater prevalence of CKD among those with diagnosed hypertension, and a similar (but non-significant) trend was seen among those with undiagnosed and pre-hypertension. Self-reported diabetes was associated with very high adjusted prevalence of CKD in all hypertension groups, including 43.4% of those with diabetes and undiagnosed hypertension and 21.0% of those with diabetes and pre-hypertension. Smoking history, insurance status, and having a routine healthcare site had no relationship with CKD in any category of blood pressure.
CKD awareness was assessed across blood pressure groups. Awareness was 2.0%, 2.2%, 3.5%, and 9.1%, among those with CKD and normal blood pressure, pre-, undiagnosed and diagnosed hypertension, respectively ().
Prevalence of CKD awareness (%), by hypertension status, NHANES 1999–2006
A sensitivity analysis examining the inclusion of reported anti-hypertensive medication use in the definition of diagnosed hypertension (n=17,794), regardless of measured blood pressure or self-report, revealed similar results to the primary definition used above (data not shown).
Sensitivity analyses of various measures of kidney disease revealed that the presence of micro-albuminuria was more common across the diagnostic continuum of hypertension than was the presence of decreased eGFR (). Micro- or macro-albuminuria were more common among younger persons (mean age 42.5 years) while eGFR <60 ml/min/1.73m2
was more common among older persons (mean age 72.4 years). Stricter definitions of kidney disease (eGFR < 45 ml/min/1.73m2
or macro-albuminuria) resulted in much lower, but still substantial, CKD prevalence, with similar patterns across blood pressure categories (). Compared to other measures of kidney disease, macro-albuminuria had the strongest association with increasing blood pressure category. The use of the CKD-EPI equation yielded similar, but slightly attenuated estimates to our primary analysis (CKD prevalence of 26.0%, 20.5%, 16.0% and 12.3 % for the diagnosed, undiagnosed, pre-hypertension, and normal blood pressure groups, respectively). Adjustment for estimated persistence of albuminuria19
also resulted in slightly lower CKD prevalence across categories (24.5%, 14.8%, 14.9%, and 4.9%, respectively).
* Adjusted prevalence of various measures of kidney disease by hypertension status, NHANES 1999–2006.