Cystatin C with Glomerular Filtration Rate, Estimated (eGFR)

Test Code
CYSTATIN C(94588)

Quest Code
94588

CPT Codes
82610

Preferred Specimen
1 mL serum

Minimum Volume
0.5 mL

Other Acceptable Specimens
Plasma collected in: EDTA (lavender-top), or sodium heparin (green-top) tube

Instructions
Collect blood in a red-top (no gel) or SST vacutainer. For red-top vacutainer, allow blood to clot (10 to 15 minutes) at room temperature. Separate serum from cells. If sample is collected in glass collection tube, transfer to plastic container.
Serum samples must be completely coagulated and, after centrifugation, must not contain any particles or traces of fibrin.

Transport Temperature
Room temperature

Specimen Stability
Room temperature: 26 days
Refrigerated: 26 days
Frozen: 10 years

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Anticoagulants other than EDTA or heparin • Whole blood sample not spun or separated • Patients less than 20 years old

Methodology
Particle Enhanced Turbidimetric Immunoassay (PETIA)

Setup Schedule
Tue, Fri

Report Available
2 to 4 Day(s)

Reference Range
See Laboratory Report

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).

Performing Laboratory
Quest Diagnostics Nichols Institute
33608 Ortega Hwy
San Juan Capistrano, CA 92675-2042



The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.