Cystatin C (CysC)

CysC is a 13-kDa, nonglycosylated basic protein that is produced by all nucleated cells. It is a cysteine protease inhibitor. Cystatin C is present in all investigated body fluids and is not affected by age, gender, muscle mass, or the inflammatory process. Cystatin C is removed from circulation by glomerular filtration and is completely reabsorbed and degraded in the tubules. Therefore, the plasma concentration of cystatin C is almost exclusively determined by the GFR, making cystatin C an excellent indicator of GFR.

Normal range:

0 " “3 months: 0.8 " “2.3 mg/L

4 " “11 months: 0.7 " “1.5 mg/L

1 " “3 years: 0.5 " “1.3 mg/L

4 " “8 years: 0.5 " “1.3 mg/L

9 " “17 years: 0.5 " “1.3 mg/L

≥18 years: 0.5 " “1.0 mg/L

Use

New marker to estimate GFR independent of gender, age, and muscle mass, and cirrhosis; does not need to be corrected for height or weight. It is superior to serum creatinine.

Sensitive marker of allograft function (although it may not be an optimal marker in patients receiving glucocorticoids).

In the assessment of adverse cardiovascular events (CHF, ischemia, death) because kidney dysfunction is associated with such events.

Interpretation

Increased In

Glucocorticoid treatment

May also be affected by thyroid disorders

Limitations

Due to immaturity of renal function in neonates, cystatin C levels are higher in those <3 months of age.

Increased levels can be associated with higher levels of CRP or BMI and steroid use.

In transplant patients, extrarenal elimination at higher levels and higher intraindividual variation compared to serum creatinine.