Glomerular filtration rate (GFR) is the best way to measure how well your kidneys are working, but this test is complicated and cannot be easily done in a doctor’s office. To get around this, laboratories use mathematical equations to estimate the glomerular filtration rate instead of measuring it. This is why laboratories report estimated GFR or eGFR.
Two commonly used estimating equations for eGFR are the CKD MDRD (Modification of Diet in Renal Disease) and the CKD EPI (Chronic Kidney Disease Epidemiology Collaboration) equations. Using these math equations, eGFR is calculated from the amount of creatinine in the blood.
Creatinine is a waste product that comes from the normal wear and tear on your body’s muscles and also from the foods you eat. Everyone has creatinine in their bloodstream. However, creatinine levels can differ between people. This reason for this difference may not only be related to kidney disease – it may be affected by several other factors, such as age, sex, and body weight.
Race was originally included in eGFR calculations because clinical trials demonstrated that people who self-identify as Black/African American can have, on average, higher levels of creatinine in their blood. It was thought the reason why was due to differences in muscle mass, diet, and the way the kidneys eliminate creatinine. Since a patient’s race is not always used when laboratory tests are ordered, laboratories used different eGFR calculations for African American and non-African American and included both numbers in their lab results.
The use of race in calculating eGFR has been a subject of debate. Race is not a biological concept, but a social construct. Using race as a factor for calculating eGFR does not account for the diversity within communities of color. Also, people who self-identify as multiracial might not want to be put in a single racial bucket.