Normal values for creatinine vary by age, gender, and ethnicity of the patient. Due to these factors, adjustments are made in equations to ensure that goals and thresholds are set equitably, allowing comparisons across the population. Without adjustment, over- or under-estimation of GFR when using creatinine as a biomarker can occur.
In general, the following are observed (Jin, 2008):
- Larger patients have higher GFR than smaller patients
- Older patients have lower GFR than younger patients
- Men have higher GFR than women
The National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) created a task force in 2020 to assess the inclusion of race in the eGFR equation. The findings of that task force determined that race should be excluded as a factor because race is subjective and a social construct; inclusion of this factor could lead to misdiagnosis and incorrect stratification.
The final NKF-ASN Task Force report recommends:
- The use of the CKD-EPI 2021 eGFR creatinine equation for calculating eGFRcr in adults.
- This new equation is recommended because a race coefficient is not included in its computation and reporting. The CKD-EPI 2021 eGFR creatinine equation included diversity in its development and does not disproportionately affect any one group.
- It is recommended that increased use of cystatin C combined with creatinine is used as a confirmatory assessment of GFR or kidney function.
