Which substance is measured as an alternative to creatinine for evaluating GFR?

Cystatin C is a protein that is produced by all nucleated cells at a relatively constant rate. It is filtered by the glomeruli of the kidneys and serves as a useful biomarker for assessing glomerular filtration rate (GFR). The reason cystatin C is often favored as an alternative to creatinine is its relative independence from muscle mass, sex, age, and diet, which can all influence creatinine levels. Elevated levels of cystatin C can indicate decreased kidney function more accurately, especially in cases where creatinine may not provide a reliable assessment due to variability in muscle mass.

In contrast, plasma urea is affected by dietary protein intake and can vary significantly with hydration status, making it less reliable as an indicator of GFR. Uric acid levels can indicate renal function but are also influenced by factors like diet and medication, making them less specific. Potassium is crucial for various bodily functions but does not directly correlate with GFR and is not used to assess kidney function. Thus, cystatin C stands out as a more stable and reliable marker for evaluating GFR compared to these other substances.