Cystatin C
Label Mnemonic: CYSTC
Epic Lab Code: LAB2967
Downtime Form: A-1a General Laboratory Requisition
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Plasma Separator Tube 4.5 mL
Minimum:
3 mL whole blood in light green top tube or ONE Microtainer® for pediatric patients.
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
0-3 months: 0.8-2.3 mg/L
4-11 months: 0.7-1.5 mg/L
1-17 years: 0.5-1.3 mg/L
18 years and older: 0.5-1.0 mg/L

Pediatric reference ranges from reference 1.
Comments:
Cystatin C is produced by all nucleated cells at a constant rate and the production rate in humans is remarkably constant over the entire lifetime. Elimination from the circulation is almost entirely via glomerular filtration. For this reason the serum concentration of cystatin C is independent from muscle mass and gender in the age range 1 to 50 years. Therefore cystatin C in plasma and serum has been proposed as a more sensitive marker for GFR, and several studies, as well as one meta analysis, have suggested that cystatin C is superior to serum creatinine for estimation of GFR. Patient groups which benefit most are those with mild to moderate kidney disease and also those in acute renal failure, where toxic drugs have to be administered which are excreted by glomerular filtration, especially elder people (> 50 years), children, pregnant women with suspicion of pre-eclampsia, diabetics, people with diseases of skeletal muscle and renal transplant recipients. Additionally cystatin C has been discussed in recent literature as a prognostic marker for acute heart failure.

References:
1. Finney H, Newman DJ, Thakkar H, Fell JME, Price CP. Reference ranges for plasma cystatin C and creatinine measurements in premature infants, neonates, and older children. Arch Dis Child 2000;82: 71- 75.

2. Levey AS, Coresh J, Balk E, Kausz AT, Levin A, Steffes MW, et al. National Kidney Foundation practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Ann Intern Med 2003;139: 137-47.

3. Rule AD, Larson TS, Bergstralh EJ, Slezak JM, Jacobsen SJ, Cosio FG. Using serum creatinine to estimate glomerular filtration rate: accuracy in good health and in chronic kidney disease. Ann Intern Med 2004;141: 929-37.

4. Wasen E, Isoaho R, Mattila K, Vahlberg T, Kivelš SL, Irjala K. Estimation of glomerular filtration rate in the elderly: a comparison of creatinine based formulae with serum Cystatin C. J Intern Med 2004;256:70-8.

5. Kyhse-Andersen J, Schmidt C, Nordin G, Andersson B, Nilsson-Ehle P, Lindström V. Serum Cystatin C, determined by a rapid, automated particle enhanced turbidimetric method, is a better marker than serum creatinine for glomerular filtration rate. Clin Chem 1994;40:1921-6.

6. Mussap M, Dalla Vestra M, Fioretto P, Saller A, Varagnolo M, Nosadini R. Cystatin C is a more sensitive marker than creatinine for the estimation of GFR in type 2 diabetic patients. Kidney Int 2002; 61:1453-61.

7. Dharnidharka VR, Kwon C, Stevens G. Serum Cystatin C is superior to serum creatinine as a marker of kidney function: a meta analysis. Am J Kidney Dis 2002;40:221-6.

8. Risch L, Drexel H, Huber AR. Differences in glomerular filtration estimates by two cystatin C-based equations. Clinical Chemistry 2005; 51:2211-2212.

9. Grubb A, Nyman U, Björk J, Lindström V, Rippe B, Sterner G, Christensson A. Simple Cystatin C-based prediction equations for glomerular filtration rate compared with the modification of diet in renal disease prediction equation for adults and the Schwartz and the Counahan-Barratt prediction equations for children. Clinical Chemistry 2005; 51:1420-1431.
Test Limitations:
Hemolysis: No significant interference up to an H index of 1000
Lipemia (Intralipid): No significant interference up to an L index of 1000
Icterus: No significant interference up to an I index of 60
Methodology:
Particle enhanced immunoturbidimetric assay
CPT Code:
82610