Stephen Fadem, MD, FACP, FASN

Learning how well your kidney is functioning is important not only in screening and diagnosing chronic kidney disease (CKD), but in following its progress. Although there are various ways to do this, the simplest is the MDRD GFR (glomerular filtration rate) which can be calculated using a patient’s age, race, gender and a laboratory test, known as the serum creatinine. The muscles are in a constant state of being broken down and being repaired. The creatinine is a byproduct of this breakdown and is generally stable in the blood from day to day.

While the serum creatinine is an indication of kidney function, its variation with muscle mass makes using the other factors mentioned above necessary. This equation was derived from a large study published in 1994 that looked at how the modification of dietary protein would affect renal disease – hence Modification of Diet in Renal Disease (MDRD). This study required a very accurate measurement of kidney function. The investigators noticed the mathematical relationships between the accurately measured GFR, age, race, creatinine and gender, and derived the MDRD study equations still in use today. It is also referred to as the eGFR. This GFR is used to determine what stage of kidney disease one has, stages 1 and 2 being very mild, with GFRs above 60 ml/min. When the GFR is greater than 60, other markers of kidney function such as an abnormal urine or abnormal ultrasound are necessary for making the diagnosis. When the GFR is less than 60 for greater than three months, it indicates the presence of CKD.

Although the calculation involves some complicated math tricks, it was programmed for the Internet shortly after it was discovered, and is on the Web at www.mdrd.com. The National Kidney Foundation uses the same application. It has also been programmed for handheld calculators. Many laboratories routinely report the MDRD GFR along with the serum creatinine value. As more and more laboratories standardize their serum creatinine measurements to the National Institute of Standards, the equation will change slightly, but that change is also programmed and available at www.mdrd.com.

When using the program, simply key in your serum creatinine, age, race and gender and your GFR value will appear. The site will also calculate your kidney disease stage. It is important that you personally keep track of your serum creatinine and GFR values.

Stephen Fadem, MD, FACP, FASN, serves as Vice President of the AAKP Board of Directors, member of the AAKP Medical Advisory Board and Co-Medical Editor of Kidney Beginnings: The Magazine. Dr. Fadem is a practicing nephrologist in Houston, Texas.

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