Chronic kidney disease (CKD) is defined as: persistent proteinuria (urine albumin/creatinine ratio of greater than 30 mg/g in an untimed urine) or a reduced glomerular filtration rate (GFR) less than 60. The most common causes of CKD are diabetes mellitus, hypertension, and glomerulonephritis. A variety of treatments are available to slow the progression of kidney disease. For type 1 diabetics, strict control of blood glucose concentrations has been shown to limit the development of microalbuminuria. Patients with hypertension benefit from treatment with angiotensin converting enzyme (ACE) inhibitors.
Because creatinine is filtered and not appreciably re-absorbed or secreted by the kidney tubules, the serum creatinine level reflects the glomerular filtration rate (GFR). The more blood that is filtered through the kidneys, the more creatinine that is excreted from the body, and the lower the serum creatinine level. Conversely, the less blood that is filtered, the less creatinine excreted, and the higher the serum creatinine level.
Recent studies have shown that serum creatinine level used in combination with other variables is an excellent predictor of GFR. The National Kidney Foundation originally recommended using the Cockroft-Gault equation to calculate GFR. Later, it recommended replacing Cockroft-Gault with the Modification of Diet in Renal Disease (MDRD) equation.
For many years, clinical laboratories have followed the National Kidney Foundation’s recommendation to use the Modification of Diet in Renal Disease (MDRD) equation to estimate glomerular filtration rate (GFR). This equation incorporated four parameters including serum creatinine level, age, sex, and ethnic group. For any given age and serum creatinine level, the estimated GFR was the same until corrections were applied for being female and/or for being African American. Black men could have a 1.5-fold higher eGFR than non-black women with the same creatinine value. Since the clinical laboratory was not aware of a patient’s race, results were reported for both African American and non-African Americans. Physicians and nurses then had to apply the eGFR value that they believed was most apropos for their patient.
Recently, this practice has been questioned because race is a social construct, not a biological one. The MDRD equation asserted that existing organ function was different between individuals who are otherwise identical except for race. Studies have shown that GFR estimations incorporating race have restricted access to care, including kidney transplantation.
In September 2021, the National Kidney Foundation and American Society of Nephrology joint task force issued a statement entitle: ”Reassessing the Inclusion of Race in Diagnosing Kidney Diseases.” They recommended that laboratories immediately replace the MDRD equation with the CKD-EPIcr_R equation that was developed without the use of the race variable.
This new formula is:
eGFR = 142 X min(Scr/k,1)α X max(Scr/k,1)-1.200 0.9938age X 1.012 [if female]
where:
- Scr is serum creatinine,
- k is 0.7 for females and 0.9 for males
- α is -0.241 for females and -0.302 for males
- min indicates the minimum of Scr/k or 1
- max indicates the maximum of Scr/k or 1
References
Delgado C, et al. Reassessing the Inclusion of Race in Diagnosing KidneyDiseases: An Interim Report from the NKF-ASN Task Force, J Amer Soc Nephrol2021;32: https://doi.org/10.1681/ASN.2021010039
Delgado C et al, A Unifying Approach for GFR Estimation: Recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease, J Amer Soc Nephrol, published online September 23, 2021.
Inker LA et al, New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race, New Engl J Med, 2021, DOI: 10.1056/NEJMoa2102953
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