Debra J. Hain, DNS, APRN, GNP, BC, is NEED BIO, Cleveland Clinic Florida, Weston, FL. She is the Leader Designate of ANNA’s CKD Special Interest Group and a member of the South Florida Flamingo Chapter.

Most nephrology nurses are aware that the number of individuals with chronic kidney disease (CKD) is a worldwide health problem. The National Kidney Foundation (NKF) estimates that there are over 20 million people in the United States who have CKD and 20 million more who are at increased risk (NKF, n.d.a). By the year 2010, over 600,000 individuals will be receiving some form of renal replacement therapy at a projected cost of greater than $28 billion dollars a year (see Figure 1). One of the biggest problems in the U.S. is that CKD is under diagnosed and, therefore, under treated. As a result, interventions are not instituted early enough to slow the progression of the disease and prevent possible complications. To address this issue, NKF (2002) has established an operational definition and classification system for CKD (see Tables 1 & 2), which will help health care providers, including nurses, develop appropriate clinical action plans.



Understanding the eGFR
According to the NKF (2002), early screening and identification of the stage of CKD is essential for health promotion and to slow the progression of the disease. The screening for CKD, as recommended in the Kidney Disease Outcomes Quality Initiative (NKF, 2002), includes a basic metabolic profile, urinalysis, albumin and/or protein to creatinine ratio on a spot urine sample, and calculated or estimated glomerular filtration rate (eGFR). Of the screening tests recommended, it has been determined that the best indicator of kidney function is the eGFR. Use of the serum creatinine alone is not a reliable marker to screen for CKD because it may underestimate the severity of the problem. This occurs because of the wide range of normal values for serum creatinine and the factors that affect the serum concentration of creatinine. These factors include tubular secretion, generation, and extra-renal excretion of creatinine as well as older age, gender, diet, body habitus, and certain medications such as trimethoprim, cimetidine, and fibric acid derivatives (other than gemfibrizil) which increase the serum creatinine by reducing its tubular secretion. Because of these variables, the GFR must decline to less than 50% before the serum concentration of creatinine rises above the normal values, reducing its reliability of being the sole marker for kidney function.


MDRD Equation
There are different methods to determine the GFR, but, in clinical practice, the eGFR is the most cost effective and efficient method. The gold standard is an inulin infusion, iothalamate or iohexol, and measurement of the inulin clearance. This is an expensive test and not readily available outside a research center. Other methods to estimate the GFR include a 24-hour urine collection, the Cockcroft-Gault equation, and the Modification of Diet in Renal Disease (MDRD) equation. Of these two equations, the NKF, the National Institute of Diabetes and Disease of the Kidney (NIDDK), and the American Society of Nephrology (ASN) recommend the MDRD equation.
 
The MDRD equation is based on four variables: serum creatinine, age in years, gender, and race (African-American or other) (NKF, 2002).

eGFR (mL/min/1.73 m2) = 186 x (SCr)-1.154 x (age)-0.203 x (0.742 if female) x (1.210 if African-American)

Even though the equation has been extensively validated for use in Caucasian and American-African populations over the age of 18 (Woodhouse, Batten, Hendrick, & Malek, 2006), it has not been validated for other populations. Those populations not studied include other races, women who are pregnant, the elderly (over age 70), patients with severe malnutrition or obesity, and patients with paraplegia or quadriplegia. Individuals in these populations should undergo 24-hour urine collection. Despite the lack of validation in some populations, the National Kidney Disease Education Program (NKDEP) (2007) has recommended that laboratories automatically report the MDRD equation when a serum creatinine is conducted for individuals 18 years old and older. This is due to its accuracy for most of the population, given the four variables that are considered. A calculator that incorporates this formula is available on-line at the NKF website, www.kidney.org/professionals/tools (NKF, n.d.b).
 
The NKDEP has established an initiative to standardize the measurement of serum creatinine by laboratories so that the instrumentation has been calibrated to be traceable to an isotope dilution mass spectrometry (IDMS) reference method. (Vickery, Stevens, Dalton, Van Lente, & Lamb, 2006) As a result of this calibration method, there has been a second MDRD equation formulated (IDMS-Traceable MDRD Study Equation) (NKDEP, 2004) This equation is:

eGFR (mL/min/1.73 m2) = 175 x (SCr)-1.154 x (age)-0.203 x (0.742 if female) x (1.210 if African-American)

Current Strategies to Report eGFR
There are many advantages of routinely reporting the eGFR for populations 18 years and older and the greatest is that since reporting has begun there has been an increased awareness of CKD. As this trend continues, more people will be identified and appropriate interventions can be implemented leading to optimal clinical outcomes. Some of the current strategies are:

• initiation of pharmacotherapy such as angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) for aggressive blood pressure management and reducing proteinuria;
• improved glycemic control;
• dietary counseling;
• assessing and reducing cardiovascular risk factors by encouraging smoking cessation and treating dyslipidemia; and
• identification and treatment of anemia and metabolic bone disease (Woodhouse et al., 2006).

To assist health care providers, including nurses, understand the stages of CKD and to develop action plans, the NKF K/DOQI has defined the stages of CKD with associated action plans for each stage (see Table 3) (NKF, 2002).




References
National Kidney Disease Education Program (NKDEP) (2007). Suggestions for laboratories: Estimating GFR. National Institutes of Health publication. Baltimore, MD: Author. Retrieved October 31, 2007 from http://www.nkdep.nih.gov/ resources/NKDEP_Suggestn4Labs_0606_508.pdf

National Kidney Disease Education Program (NKDEP). (2004). Understanding GFR (NIH Publication No, 04-5579). Bethesda, MD: National Institutes of Health.
 
National Kidney Foundation. (n.d.a). The facts about chronic kidney disease (CKD). Retrieved October 31, 2007 from www.kidney.org/kidneydisease/ckd/index.cfm.

National Kidney Foundation (n.d.b). Clinical tools. GFR calculator. Retrieved October 24, 2007, from www.kidney.org/profes sionals/tools/

National Kidney Foundation. (2002). K/DOQI clinical practice guidelines for chronic kidney disease: Evaluation, classification and stratification. American Journal of Kidney Disease, 39(St 2). S1-246.

Vickery, S., Stevens, P.E., Dalton, R.N., Van Lente, F., & Lamb, E.J. (2006). Does the ID-MS traceable MDRD equation work and is it suitable for use with compensated Jaffe and enzymatic creatinine assays? Nephrology Dialysis Transplantation, 21(9), 2439-2445.

Woodhouse, S., Batten, W., Hendrick, H., & Malek, P.A. (2006). The glomerular filtration rate: An important test for diagnosis, staging and treatment of chronic kidney disease. Laboratory Medicine, 37(4), 244-247.

Additional Reference
National Kidney Disease Education Program (NKDEP). (2006). Rationale for use and reporting of estimated GFR (NIH Publication No. 06-5509). Bethesda, MD: National Institutes of Health.