Baseline Characteristics of Participants in the African American Study of Kidney Disease and Hypertension (AASK) Clinical Trial and Cohort Study

Background: African Americans are at increased risk of kidney failure caused by hypertension. The primary objective of the African American Study of Kidney Disease and Hypertension (AASK) Cohort Study is to identify risk factors for progressive kidney disease in African Americans with hypertensive chronic kidney disease in the setting of recommended antihypertensive therapy. Study Design, Setting, & Participants: On completion of the AASK Trial, a randomized, double-blind, 3 × 2 factorial trial, participants who had not yet begun dialysis treatment or undergone kidney transplantation were invited to enroll in a prospective Cohort Study. Cohort Study participants received recommended antihypertensive drug therapy, including high rates of angiotensin-converting enzyme-inhibitor (73%) and angiotensin receptor blocker (10%) use with a blood pressure goal of less than 130/80 mm Hg. Predictor, Outcomes, & Measurements: Baseline clinical and demographic characteristics are described separately at the baseline of the AASK Trial and Cohort Study. Results: Of 1,094 persons enrolled in the AASK Trial (June 1995 to September 2001; mean age, 55 years; 61% men), 691 enrolled in the AASK Cohort Study (April 2002 to present), 299 died or reached dialysis therapy or transplantation, and 104 declined to participate in the AASK Cohort Study. Mean baseline systolic/diastolic blood pressures were 150/96 mm Hg in the Trial and 136/81 mm Hg in the Cohort Study. Cohort Study participants had greater serum creatinine levels at the start of the Cohort Study (2.3 versus 1.8 mg/dL [203 versus 159 μmol/L]), corresponding to an estimated glomerular filtration rate of 43.8 versus 50.3 mL/min/1.73 m² (0.73 versus 0.84 mL/s/1.73 m²), than Trial participants and greater urine protein-creatinine ratios (0.38 versus 0.19 mg/mg, respectively). Individuals who were eligible, but declined to participate in the Cohort Study, had greater systolic blood pressure, but similar kidney function. Limitations: Some parameters, such as iothalamate glomerular filtration rate, urinary albumin level, echocardiogram, and ambulatory blood pressure, were not performed in both the Trial and the Cohort Study, limiting the ability to evaluate changes in these parameters over time. Conclusion: Despite well-controlled blood pressure in the AASK Trial, Cohort Study participants still had evidence of progressive chronic kidney disease. Thus, the AASK Cohort Study is well positioned to address its primary objective.