Native cystatin C (CnCn), 3Pro-OH cystatin C (CnCo), cystatin C-desS (CnCds), 3Pro-OH cystatin C-desS (CnCods) and cystatin C-desSSP (CnCdssp). CnCt is the total concentration of detected cystatin C proteoforms.
Method(s): MALDI-TOF MS (1).
Cystatin C is a non-glycosylated cysteine protease inhibitor with a molecular weight of 13 kDa. It is produced at a constant rate by nucleated cell and freely filtered by the renal glomerulus, and serum cystatin C is an established marker of renal function. Cystatin C is a more specific marker of glomerular filtration rate than creatinine, because levels are independent of age, sex, muscle mass and diet (2). In addition, high cystatin C is associated with elevated risk of death from myocardial infarction, stroke, and metabolic syndrome. Higher levels of cystatin C and the presence of certain isoforms have also been related to neurological and cerebral disorders such as cerebral amyloid angiopathy, amyotrophic lateral sclerosis, multiple sclerosis, and Alzheimer’s disease. Cystatin isoforms can be detected both in serum and cerebrospinal fluid and more than a dozen have been reported so far.
Assessment of renal function.
Matrix: EDTA plasma and serum. Cystatin C is stable for 3 month at -20 °C.
Volume: Minimum volume is 30 µL, but 100 µL is optimal and allows reanalysis.
Preparation: The blood sample must be centrifuged and the plasma/serum fraction put on ice, and frozen.
Cystatin C is stable for 3 month at -20 °C. Long-term storage requires -80 °C.
Reported values: 0-7 µg/ml.
Intraclass correlation coefficient (ICC): 0.7.
1. Gao, J., Meyer, K., Borucki, K., and Ueland, P.M. (2018). Multiplex immuno-MALDI-TOF MS for targeted quantification of protein biomarkers and their proteoforms related to inflammation and renal dysfunction. Anal Chem 90, 3366-373.
2. Ferguson, T.W., Komenda, P., and Tangri, N. (2015). Cystatin C as a biomarker for estimating glomerular filtration rate. Curr Opin Nephrol Hypertens 24, 295-300.