Decreases in glomerular filtration rate (GFR) are associated with higher risks of cardiovascular events, hospitalizations, and premature death (N Engl J Med. 2004;351:1296-1305).
While both patients and clinicians recognize the importance of accurate renal function assessments, most rely on a relatively qualitative categorization of chronic kidney disease (CKD) using plasma creatinine concentration alone.
Since creatinine is excreted solely by the kidneys, is completely filtered, and undergoes negligible tubular secretion, serum levels enable estimations of GFR, albeit imperfectly. Assessment of urinary or plasma creatinine clearance are much better measures of global renal function.
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In adults, to avoid the effort involved with direct clearance measurements, various equations for estimating GFR from serum creatinine have been devised, including the Modified Diet in Renal Disease (MDRD) study formula and the Nankivell and the Cockcroft-Gault formulas.
Too often, clinicians (probably including the majority of urologists) make important clinical judgments, such as medicinal dosing and preoperative qualitative assessments of renal reserve, based on spot serum creatinine measures. The perils of this practice are clear. While a serum creatinine level of 1.1 mg/dL in a 40-year-old African American male corresponds to a GFR of 96 mL/min/1.73 m2, the same creatinine in a healthy 62-year-old Caucasian female is nearly 50% less at 53 mL/min/1.73 m2.
In this example, the former patient has a normal clearance, whereas the latter is classified as having CKD stage III. An increase in serum creatinine to 1.9 mg/dL following radical nephrectomy in this patient (which some may find qualitatively acceptable) would be associated with a GFR of 28 mL/min/1.73 m2 (CKD stage IV) (quantitatively unacceptable) with significant implications for the next 20 years or more of her life.
Proper staging of CKD recently has been facilitated by standardized reporting of estimated GFR (eGFR) by most major commercial laboratories. This important information facilitates application of clinical practice guidelines, including those for pharmacologic dosing, appropriate administration of contrast agents, and accurate patient counseling prior to operative interventions on the kidney. The eGFR is a mandatory portion of all urologic assessments and critical to appropriate urologic decision-making.
The time has come for urologists to speak the same language as our nephrology colleagues and make a concerted effort to assess, report, and make clinical decisions based on eGFR values and not serum creatinine. Terms such as chronic renal insufficiency should be eliminated. Routine staging of CKD is an im-perative part of urologic care.
