Why is Cystatin C preferred over creatinine in some assessments of renal function?

Cystatin C is preferred over creatinine in some assessments of renal function primarily because it is not influenced by diet. Unlike creatinine, which can be affected by dietary intake of protein and certain medications, Cystatin C levels remain relatively stable. This characteristic makes Cystatin C a more reliable biomarker for kidney function, especially in situations where dietary changes might lead to fluctuations in creatinine levels.

Furthermore, Cystatin C is produced at a constant rate by all nucleated cells and is cleared primarily by the kidneys, but its levels are less impacted by other factors such as muscle mass, age, and sex. This gives it an advantage in accurately reflecting renal function in diverse populations. It is also important to note that while factors like age and sex do affect serum creatinine levels, Cystatin C offers a more consistent measure in comparing kidney function across individuals with varying body compositions.