Cystatin C

Label Mnemonic:	CYSTC
Epic code:	LAB2967
Downtime form:	Doctor/Provider Orders - Pathology Core and Specialty Care Nursery

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 an alternative marker for estimated glomerular filtration rate (eGFR).

On August 16, 2022, the University of Iowa Hospitals and Clinics (UIHC) introduced two eGFR calculations based on cystatin C. The first uses the 2012 cystatin C-based CKD-EPI equation which does not contain any race-based variables. This calculation is performed for all serum/plasma cystatin C orders. This will be resulted as a separate eGFR component below the cystatin C value in Epic as "eGFRcys (CKD-EPI 2012)". The second cystatin C-based eGFR equation uses the 2021 eGFRcr-cys(CKD-EPI) refit without race variable equation. This calculation will be performed for all serum/plasma specimens for which both creatinine and cystatin C are ordered. This will be resulted as a separate eGFR component below the cystatin C value in Epic as "eGFRcys-cr (CKD-EPI 2021)".

Cystatin C-based equations represent an alternative to eGFR equations based on creatinine alone and may offer advantages in some clinical situations (e.g., spinal cord injury with skeletal muscle loss) that may impact creatinine-based equations.

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. National Kidney Foundation

3. National Kidney Disease Education Program (NKDEP)

4. National Kidney Foundation eGFR Calculator

5. Delgado C et al. A Unifying Approach for GFR Estimation: Recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. Am J Kidney Dis. 2022 Feb;79(2):268-288.e1. doi: 10.1053/j.ajkd.2021.08.003.

See Additional Information:
Glomerular Filtration Rate (GFR)

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