Abstract
Kidney function is primarily assessed through glomerular filtration rate (GFR), with serum creatinine being the most commonly used marker in clinical practice. However, creatinine levels can be influenced by factors such as age, sex, muscle mass, and diet, which may affect the accuracy of estimated GFR (eGFR). The CKD-EPI formula is widely used due to its performance across various stages of kidney function, and the 2021 update removed race correction. While this change is important, contributing to minimizing longstanding healthcare disparities, it may still lead to challenges in interpreting results, particularly in certain populations. Estimated GFR based on the combination of serum creatinine and cystatin C was associated with greater accuracy compared with the use of each biomarker alone, and is beneficial for patients with conditions that affect creatinine levels. It should be noted that cystatin C may also be influenced by factors such as inflammation and thyroid dysfunction. In the future, it is possible that such formulas include multiple biomarkers to further improve accuracy. However, widespread adoption of these approaches will require validation and evaluation of cost-effectiveness. When interpreting eGFR results, it is crucial to account for individual factors such as muscle mass, age, and comorbid conditions. In cases of extreme muscle mass or other complicating factors, measured GFR may be necessary. Ultimately, eGFR is a useful screening tool, but it is an estimation of GFR, then clinical judgement and individualized approaches remain essential for accurate assessment and management of kidney function.