This text can be used or modified to meet the needs of the laboratory, health care professionals and patients.
Effective <DATE>, our laboratory is changing the calculation of estimated glomerular filtration rate (eGFR) from creatinine to the new CKD-EPI 2021 equation that does not include a race coefficient. The new equation is recommended by the National Kidney Foundation and the American Society of Nephrology’s Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. The new eGFRcr equation has similar overall performance characteristics to the older equations and has been assessed to not have potential consequences that disproportionately affect any one group of individuals. For most patients the eGFRcr result will be similar, however, for some, the values may differ by more than 10% particularly at higher values of eGFRcr and for younger adult ages. Please go to eGFR Calculator | National Kidney Foundation to compare the new CKD-EPI 2021 eGFRcr result with a previously calculated eGFR based on older equations.
The eGFRcr values using the new equation will only report one value and will use nomenclature to distinguish results from the older equations. Results will not trend with those using the older equations. The new report name is eGFRcr (calculated using only creatinine)
<INCLUDE THE NEXT SENTENCE IF APPLICABLE FOR A LABORATORY.> We are also introducing the Kidney Profile order that includes both creatinine with calculated eGFRcr and urine albumin-creatinine ratio (uACR). Clinical practice recommendations suggest ordering uACR with serum creatinine to facilitate appropriate classification of patients with chronic kidney disease, to assess risk for progression and to monitor patients at risk to develop CKD.
When evaluating a patient’s GFR, it is important to remember that eGFR is an estimate of the patient’s GFR. For eGFRcr and eGFRcys (calculated from cystatin C), 80-90% of values are within 30% of measured GFR. eGFRcr-cys (calculated using both creatinine and cystatin C) is more accurate than either eGFRcr or eGFRcys alone.
eGFRcr values need to be interpreted based on clinical context. Clinical practice recommendations suggest ordering cystatin C as a confirmatory test for patients with eGFRcr of 45-59 mL/min/1.73m2 with uACR <30 mg/g, and in patients for whom the creatinine may be a less reliable indicator of GFR near decision points. eGFRcr-cys provides a more accurate estimate of GFR. In addition, eGFRcys may be more accurate in conditions when creatinine is a less reliable test for estimating the GFR. Situations in which non-GFR factors may have a large affect on serum creatinine include alterations in creatinine generation (muscle wasting diseases, amputees, body builders, vegan diet), drugs that affect tubular secretion of creatinine (cimetidine, cobicistat, dolutegravir, fenofibrate, ritonovir, trimethoprim and others), and conditions with extra-renal elimination of creatinine (gastrointestinal and “third-space” losses). Clinicians must also consider non-GFR factors affecting cystatin C, including smoking, obesity, inflammation and disorders of thyroid or adrenal hormones.
Delgado C, Baweja M, Crews DC, 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. Am J Kidney Dis. 2021 DOI: 10.1053/j.ajkd.2021.08.003
Inker LA, Eneanya ND, MCorsh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. New England J Med. 2021: DOI: 10.1056/NEJMoa2102953