Cystatin C, Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Cystatin C is a low molecular weight (13,250 kD) cysteine Proteinase inhibitor that is produced by all nucleated cells and found in body fluids, including serum. Since it is formed at a constant rate and freely filtered by the kidneys, its serum concentration is inversely correlated with the glomerular filtration rate (GFR); that is, high values indicate low GFRs while lower values indicate higher GFRs, similar to creatinine.
The renal handling of cystatin C differs from creatinine. While both are freely filtered by glomeruli, once it is filtered, cystatin C, unlike creatinine, is reabsorbed and metabolized by proximal renal tubules. Thus, under normal conditions, cystatin C does not enter the final excreted urine to any significant degree.
The serum concentration of cystatin C remains unchanged with infections, inflammatory or neoplastic states, and is not affected by body mass, diet, or drugs. Thus, cystatin C may be a more reliable marker of renal function (GFR) than creatinine.
As an index of glomerular filtration rate, especially in patients where serum creatinine may be misleading (eg, very obese, elderly, and malnourished patients)
Assessing renal function in patients suspected of having kidney disease
Monitoring treatment response in patients with kidney disease
Elevated levels of cystatin C indicate decreased glomerular filtration rate
Due to immaturity of renal function in neonates, cystatin C levels are higher in those <3 months of age.(1)
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Lipemic or frozen specimens, which become turbid after thawing, may interfere with the assay.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =23 years: 0.57-1.29 mg/L
Reference values have not been established for patients that are <23 years of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Finney H, Newman DJ, Thakkar H, et al: Reference ranges for the plasma cystatin C and creatinine measurements in premature infants, neonates, and older children. Arch Dis Child 2000 Jan;82(1):71-75
2. Buehrig CK, Larson TS, Bergert JH, et al: Cystatin C is superior to serum creatinine for the assessment of renal function. J Am Soc Nephrol 2001;12:194A
3. Grubb AO: Cystatin C - properties and use as a diagnostic marker. Adv Clin Chem 2000;35:63-99
4. Coll E, Botey A, Alvarez L, et al: Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment. Am J Kidney Dis 2000 Jul;36(1):29-34