Research Updates in Kidney and Urologic Health

New GFR Calculation Facilitates Monitoring of Kidney Function

Laboratories Urged to Include GFR Calculation in Routine Blood Work

Researchers and clinicians agree that the most accurate measure of kidney function is the glomerular filtration rate (GFR). Measuring GFR used to require a 24-hour urine collection and a blood sample, thus making regular measurements impractical. In recent years, however, researchers in the Modification of Diet in Renal Disease (MDRD) trial, sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), developed a GFR calculation that requires only a serum creatinine value along with the patient's weight, race, and sex.

In addition to making monitoring a patient's kidney function easier, the MDRD GFR calculation has allowed researchers to use data from the National Health and Nutrition Examination Survey to estimate the prevalence of chronic kidney disease in the United States.

The National Kidney Foundation (NKF) has used the GFR formula and prevalence estimates to develop a clear definition of chronic kidney disease, identify disease stages, and offer treatment guidelines for the different stages. The NKF's Kidney Disease Outcomes Quality Initiative (K/DOQI) practice guidelines for chronic kidney disease were published in 2002.

The K/DOQI guidelines define chronic kidney disease as a GFR that remains below 60 mL/min/1.73 m² for more than 3 months. The new guidelines also identify five stages of the disease and recommend actions to take at each stage.

• Stage 1 comprises patients who have kidney damage but a normal GFR (90 or higher). The recommended actions are to diagnose and treat the cause of the kidney damage, treat comorbid conditions, slow the progression of chronic kidney disease, and reduce cardiovascular risk factors.
  
  
• Stage 2 comprises patients with a mild reduction in GFR (60 to 89). The recommended action is to estimate disease progression.
  
  
• Stage 3 consists of a moderate GFR reduction (30 to 59). The recommended actions are to evaluate and treat complications such as anemia and bone disease.
  
  
• Stage 4 consists of a severe GFR reduction (15 to 29). The recommended action is to prepare the patient for kidney replacement therapy.
  
  
• Stage 5 consists of kidney failure, marked by a GFR below 15. The recommended action is to initiate kidney replacement therapy—either dialysis or transplantation—if uremia is present.

NIDDK scientists and NKF officials urge medical laboratories to provide a GFR value based on serum creatinine in routine blood analyses.

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