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CYSTATIN C WITH GLOMERULAR FILTRATION RATE, ESTIMATED (eGFR)
Test CodeLAB1460
CPT Codes
82610
Preferred Specimen
7ml Gold Top Tube
Other Acceptable Specimens
Red, Light Green or Dark Green
Instructions
Sample must be centrifuged within 2 hours of collection. Serum/plasma must be removed from the red cells and put into aliquot tubes following centrifugation.
Transport Temperature
Refrigerated
Specimen Stability
Centrifuge within 2 hours of collection.
Room Temperature: 14 days
Refrigerated: 21 days
Frozen: 5 years
Room Temperature: 14 days
Refrigerated: 21 days
Frozen: 5 years
Methodology
Particle Enhanced Turbidimetric Immunoassay (PETIA)
Setup Schedule
Sunday-Saturday
Reference Range
0-2 years old: no reference range established
2-19 years old: 0.62-1.11 mg/L
≥ 20 years old: 0.50-1.20 mg/L
2-19 years old: 0.62-1.11 mg/L
≥ 20 years old: 0.50-1.20 mg/L
Clinical Significance
Cystatin C is a non-glycosylated, 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 the 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.GFR can be estimated (eGFR) from serum cystatin C utilizing an equation which includes the age and gender of the patient. The CKD-EPI cystatin C equation was developed by Inker et al, and demonstrated good correlation with measured iothalamate clearance in patients with all common causes of kidney disease, including kidney transplant recipients. Cystatin C eGFR may have advantages over creatinine eGFR in certain patient groups in whom muscle mass is abnormally high or low (for example quadriplegics, very elderly, or malnourished individuals). Blood levels of cystatin C also equilibrate more quickly than creatinine, and therefore, serum cystatin C may be more accurate than serum creatinine when kidney function is rapidly changing (for example amongst hospitalized individuals).
Males:
When Cystatin C is ≤0.8, eGFR=133 x (Scys/0.8)-0.499 x 0.966age
When Cystatin C is >0.8, eGFR=133 x (Scys/0.8)-1.328 x 0.966age
Females:
When Cystatin C is ≤0.8. eGFR=133 x (Scys/0.8)-0.499 x 0.966age x 0.932
When Cystatin C is >0.8. eGFR=133 x (Scys/0.8)-1.328 x 0.996age x 0.932
Stage, GFR, Classification:
G1, ≥90, normal or high
G2, 60-89, Mildly decreased
G3a, 45-59, Mildly or Moderately decreased
G3b, 30-44, Moderately to Severely decreased
G4, 15-29, Severly decreased
G5, <15, Kidney Failure
In the absence of kidney damage, neither G1 or G2 fullfil criteria for CKD per KDIGO.
Males:
When Cystatin C is ≤0.8, eGFR=133 x (Scys/0.8)-0.499 x 0.966age
When Cystatin C is >0.8, eGFR=133 x (Scys/0.8)-1.328 x 0.966age
Females:
When Cystatin C is ≤0.8. eGFR=133 x (Scys/0.8)-0.499 x 0.966age x 0.932
When Cystatin C is >0.8. eGFR=133 x (Scys/0.8)-1.328 x 0.996age x 0.932
Stage, GFR, Classification:
G1, ≥90, normal or high
G2, 60-89, Mildly decreased
G3a, 45-59, Mildly or Moderately decreased
G3b, 30-44, Moderately to Severely decreased
G4, 15-29, Severly decreased
G5, <15, Kidney Failure
In the absence of kidney damage, neither G1 or G2 fullfil criteria for CKD per KDIGO.
Performing Laboratory
West Virginia University Hospitals, Inc.
