Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Abstract: Mathematical models have been used since 1976 in an attempt to predict the progression of chronic renal failure. These models have used the serum creatinine level as either a reciprocal or logarithmic plot against time. The accuracy of such predictions are characterized by either a correlation coefficient (r value) or prediction error (time at which dialysis was predicted minus time at which dialysis actually occurred). Retrospectively, we analyzed 37 children who progressed to end-stage renal disease, grouped them by their respective primary diseases, and calculated both r values and prediction error for each individual and group. Although r values for each group (with the exception of patients less than 1 year of age) were comparable, prediction errors were widely disparate among the various groupings. Individuals within each of the groups had disparate values even though identical r values were present. These observations indicate that predictive models using serum creatinine levels are of limited clinical use and are least useful for patients younger than 1 year of age.
Creatinine