This article discusses the importance of accurately estimating glomerular filtration rate (GFR) in medical care and clinical decision-making. The current guidelines recommend using serum creatinine as the initial test and an estimating equation to calculate GFR. If the estimated GFR is considered less accurate, confirmatory testing with cystatin C is recommended. However, the performance of cystatin C as a GFR marker in real-world settings is not well-studied. A recent study found that using both creatinine and cystatin C for estimating GFR outperforms using either marker alone, particularly when there is discordance between the two markers. The study also highlights the impact of rounding levels of kidney function markers on the performance of GFR-estimating equations, emphasizing the need for accurate measurement and reporting of creatinine and cystatin C values. [Extracted from the article]