[Effect of Arterial Pressure and Age on Renal Function, The "Care for the Kidney" Study]

Background: The kidney is one of the principal target organs of hypertension. The mechanism by which hypertension damages the kidney and the relative contribution of high blood pressure to the progression of renal failure remains incompletely defined. The clinical quantification of renal function is usually thought to require determination of plasma clearance of endogenous creatinine (ClCr), an impractical test for epidemiological evaluation. For this reason several formulae have been proposed to estimate the ClCr from the serum creatinine concentration, such as sex, age, and body weight. The most often used formula is the one proposed by Crockroft and Gault in 1976.

Objective: To determine the prevalence of loss of renal function and the influence of hypertension and age on this loss in hypertensive and normotensive patients.

Patients And Method: An observational, cross-sectional comparative study was carried out. 3,420 patients (1,171 normotensive and 2,249 hypertensive) were studied. Average age was 70 years (19.4% of patients < 65 years; 23.3% > 75 years). 98.1 of hypertensive patients were treated with drugs, 26.7% of them with more than one drug. 27.9% of treated patients achieved blood pressure control (< 140-90 mm Hg). The level of renal function was estimated by means of ClCr using the Crockroft and Gault formula.

Results: 3.9% of normotensive and 12.2% of hypertensive patients had serum creatinine values > 1.3 mg/dl, but 28.6% of normotensive and 40.4% of hypertensive had ClCr < 60 ml/min. The patients over 75 years had ClCr mean values < 60 ml/min. There was correlation between ClCr and age, but there was no correlation between ClCr and blood pressure values.

Conclusions: The estimated ClCr decrease with age and there existed correlation between both variables. The ClCr is lower in hypertensive than in normotensive patients. Hypertension and age influence loss of renal function, but age is a determining factor. The estimated ClCr was a more sensible method of evaluating the loss of renal function than the serum creatinine values. The use of Crockroft and Gault formula can be useful for making diagnostic and therapeutic decisions in primary care.