Relationship Between Blood Pressure and Renal Indices Among Chronic Renal Insufficiency Patients in a Large Cohort Study

Objective: To examine the effect of blood pressure on serum creatinine and GFR in patients with chronic kidney disease (CKD).Design and method: Chronic Renal Insufficiency Cohort (CRIC) study enrolled 3,939 participants with CKD aged 21 to 74 years and followed them from 2003 to 2013. We categorized Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) into three levels: SBP < =120 as low, SBP 121–140 as medium, and SBP > 140 as high; DBP < =70 as low, DBP 71–85 as medium and DBP > 85 as high. We examined the relationship of these blood pressure levels with two renal indices over time, using Generalized Estimating Equation (GEE) and Curve Fitting methods. Results: GEE results showed that after controlling for confounding factors (smoking, BMI, ACE/ARB, diabetes and age), the predicted eGFR was 5.18 units higher (p < 0.01) when SBP was low as compared to high and 4.0 units higher (p < 0.01) when SBP was medium as compared to high. The SCr value was 0.52 units lower (p < 0.01) with low SBP as compared to high and 0.43 units lower when SBP was medium as compared to high. The Curve Fitting results show that eGFR has a downward “U” shape with SBP; eGFR was highest when SBP was around 100 and starts to decline either with SBP > 100 or SBP < 100. Consistently, the relationship between SCr was an upward “U” shape with SBP. While looking at DBP and renal indices, GEE showed that the eGFR was 1.2 units lower (p = 0.112) when DBP was low as compared to high and 1.15 units higher (p = 0.08) when DBP was medium as compared to high. The Curve Fitting results show that the eGFR starts to decline when DBP is less than 75 and stays fairly constant when DBP is 75 or higher. Conclusions: Renal function in CKD patients is affected by low or high SBP either side of 100 mm of Hg, whereas DBP affects renal function primarily when it is lower than 75 mm of Hg. DBP should be given careful consideration so as not to lower it too aggressively while managing hypertension in CKD patients.