Also two previous large randomized clinical trials, including the Modification of Diet in Renal Disease trial and the African American Study of Kidney Disease and Hypertension trial, have failed to find a significant relationship between intense blood pressure control and glomerular filtration rate decline among CKD patients. However, in secondary analyses, progression of CKD among those with a higher baseline proteinuria was significantly delayed in the MDRD trial and a similar favorable trend was also shown in the AASK trial. Very recently, the long-term follow-up study of the AASK trial further supported this view among patients with higher proteinuria. These findings indicate that the association between hypertension and CKD is complicated. In this study, we tested our hypothesis that the association between high blood pressure and renal function is modified by albuminuria status. In a nationally representative study population, we found even among adults without known CKD, diabetes or cardiovascular diseases, the prevalence of reduced renal function, prehypertension and undiagnosed hypertension was still high. Furthermore, we found prehypertension or undiagnosed hypertension was associated with reduced kidney function only among those with albuminuria, but not among those without. Strict blood pressure control has been considered the basis of therapy for slowing renal deterioration. However, very recently, the follow-up ABT-199 cohort study for the AASK trial showed that among African Americans, intensive BP control had no overall effect on CKD progression, but there was a potential benefit in patients with albuminuria. A pooled analysis showed that a lower BP goal might delay decline in GFR among patients with a greater urine protein excretion. The underlying mechanism remains unknown. However, a number of previous studies have shown that not only albuminuria levels but also albuminuria changes can be used to predict cardiovascular and renal outcomes. Even among the patients with a so-called normal threshold of microalbuminuria, an increased risk of total mortality and cardiovascular and renal events in patients with albuminuria between 10 and 30 mg/g creatinine was observed as compared with the patients with albuminuria less than 10 mg/g. The follow-up cohort study for MDRD trial did not find the modification effect by albuminuria as shown in the initial trial. It is possible that the inconsistent result is because more participants in the intensive BP control group used angiotensin-convertingenzyme inhibitors in the MDRD study. The association between high blood pressure and renal insufficiency is complex and multifactorial. It is believed hypertension and CKD may mutually be both the cause and consequence of each other. A causal relationship is hard to draw from previous human studies investigating the association.