Confounding Factors for the Compilation of the Risk Score

The compilation of the risk score for chronic kidney disease ought to take into account confounding factors such as the impact of prehypertension,suboptimal predictive value of creatinine-based glomerular filtration rate (GFR),and suboptimal predictive value of a single measurement of GFR. Although a baseline blood pressure of 140/90 mm Hg or more was the one utilized for evaluating the likelihood of subsequent deterioration in renal function,it is now recognized that even baseline blood pressures in the prehypertensive range (systolic blood pressure 120 mm Hg or more and <140 mm Hg;diastolic blood pressure 80 mm Hg or more and <90 mm Hg) have an impact on renal function. In a study that enrolled 17,794 subjects aged 20 years or more,after correction for age,sex,and race,prevalence of chronic kidney disease amounted to 13.4% among patients with blood pressure <120/80 mm Hg,17.3% among those with prehypertension,and 27.5% among those with diagnosed blood pressure amounting to 140/90 mm Hg or more. This upward trend was highly significant (P <.001). The choice of parameter for evaluating baseline renal function also is crucial given the recognition (based on a review of 12 studies comprising a total of 12,898 patients) that the Modification of Diet in Renal Disease (MDRD) formula performs better at lower GFR ranges,and the Chronic Kidney Disease Epidemiology (CKD-EPI) formula is better at higher GFR ranges. The predictive accuracy of creatinine-based evaluation of GFR (using the CKD-EPI equation) can be improved by concurrent evaluation of cystatin-C GFR and urine albumin-to-creatinine ratio (ACR). In the latter prospective cohort study involving 26,643 white as well as black adults aged 45 years or more,among those initially classified as not having chronic kidney disease defined by GFR creatinine,those with chronic kidney disease defined by GFR cystatin C plus ACR had the largest multivariate adjusted hazard ratio (HR) of death (HR 3.0;95% confidence interval,2.4-3.7). The suboptimal predictive accuracy of creatinine-based GFR (using the MDRD formula) is compounded by the fact that,among 512 subjects aged 15-75 years,a single test indicating chronic kidney disease had a positive predictive value of only 0.5 for repeat abnormality 3 months later.
The American Journal of Medicine

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