Which statement regarding Cystatin C is true?

Cystatin C is indeed measured immunochemically, which means that specific antibodies are used to quantify the concentration of Cystatin C in the blood. This method allows for the sensitive detection of this protein and is utilized because of its potential as a reliable biomarker for estimating kidney function, particularly in individuals where renal function may not be accurately reflected by serum creatinine levels.

Measuring Cystatin C immunochemically provides a robust assessment because it is less influenced by muscle mass compared to creatinine, making it a valuable tool in clinical settings, especially for detecting early changes in kidney function.

The other statements regarding the calibrator for Cystatin C, the coefficient of variation in assays compared to plasma creatinine, and the consistency of enzymatic and rate Jaffe reactions for creatinine do not align with current understandings and practices regarding Cystatin C measurement.