Xuelei Wang

The African American Study of Kidney Disease and Hypertension (AASK) was conducted over a 7-year period at 21 clinical centers across the United States to investigate whether one of two levels of blood pressure control and/or one of three classes of antihypertensive medications was more effective at slowing the rate of renal disease in African Americans with renal insufficiency presumed secondary to hypertension. Analysis at the end of the study revealed an overall participant retention rate of 90% (still alive and not on dialysis); defined as having had at least one 125I-iothalamate GFR, the primary data collection element, measured in the final year of the study. Adherence, defined as not missing 3 consecutive protocol visits (6 months) during the study, was 77%. Adherence to protocol visits showed that participants assigned to a low blood pressure goal (mean arterial pressure [MAP] of 92 mm/Hg or lower) had a 30% (95% CI, 9%-45%) lower risk of nonadherence as compared to those assigned to the usual goal [MAP of 102-107] (p = 0.006). No statistically significant difference was observed between randomized drug assignments. Higher baseline systolic (p = 0.0001) and diastolic (p = 0.007) blood pressures were associated with a higher risk of nonadherence. Declining to provide an annual income is associated with a higher risk of nonadherence compared to those with incomes of $15,000 or higher (p = 0.04). In discussing the identifying factors that may predict nonadherence and the strategies that assisted in improving adherence and retention, this article offers insights for researchers in achieving high levels of participation in long-term clinical studies.

Whereas much research has investigated equations for obtaining estimated GFR (eGFR) from serum creatinine in cross-sectional settings, little attention has been given to validating these equations as outcomes in longitudinal studies of chronic kidney disease. A common objective of chronic kidney disease studies is to identify risk factors for progression, characterized by slope (rate of change over time) or time to event (time until a designated decline in kidney function or ESRD). The relationships of 35 baseline factors with eGFR-based outcomes were compared with the relationships of the same factors with iothalamate GFR (iGFR)-based outcomes in the African American Study of Kidney Disease and Hypertension (AASK; n = 1094). With the use of the AASK equation to calculate eGFR, results were compared between time to halving of eGFR or ESRD and time to halving of iGFR or ESRD (with effect sizes expressed per 1 SD) and between eGFR and iGFR slopes starting 3 mo after randomization. The effects of the baseline factors were similar between the eGFR- and iGFR-based time-to-event outcomes (Pearson R = 0.99, concordance R = 0.98). Small but statistically significant differences (P < 0.05, without adjustment for multiple analyses) were observed for seven of the 35 factors. Agreement between eGFR and iGFR was somewhat weaker, although still relatively high for slope-based outcomes (Pearson R = 0.93, concordance R = 0.92). Effects of covariate adjustment for age, gender, baseline GFR, and urine proteinuria also were similar between the eGFR and iGFR outcomes. Sensitivity analyses including death in the composite time-to-event outcomes or using the Modification of Diet in Renal Disease equation instead of the AASK equation provided similar results. In conclusion, the data from the AASK provide tentative support for use of outcomes that are based on an established eGFR formula using serum creatinine as a surrogate for measured iGFR-based outcomes in analyses of risk factors for the progression of kidney disease.