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Test ID CYSTC Cystatin C with Estimated GFR, Serum

Useful For

Cystatin C:

An index of glomerular filtration rate, especially in patients where serum creatinine may be misleading (eg, very obese, elderly, or malnourished patients)

 

Assessing renal function in patients suspected of having kidney disease

 

Monitoring treatment response in patients with kidney disease

 

Estimated Glomerular Filtration Rate (eGFR):

An index of GFR, especially in patients where serum creatinine may be misleading (eg, very obese, elderly, or malnourished patients); for such patients, use of CKD-EPI cystatin C equation is recommended to estimate GFR

 

Assessing renal function in patients suspected of having kidney disease

 

Monitoring treatment response in patients with kidney disease

Method Name

Immunoturbidimetric

Reporting Name

Cystatin C with Estimated GFR, S

Specimen Type

Serum

Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Specimen Volume: 1 mL  

Forms: If not ordering electronically, complete, print, and send a Cardiovascular Test Request Form (T724) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/cardiovascular-request-form.pdf).

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Ambient  7 days
  Frozen  7 days

Clinical Information

Cystatin C:

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.

 

Estimated Glomerular Filtration Rate (GFR):

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:(1) 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).

Reference Values

CYSTATIN C

Males:

0 days-22 years: no reference values established

23-29 years: 0.60-1.03 mg/L

30-39 years: 0.64-1.12 mg/L

40-49 years: 0.68-1.22 mg/L

50-59 years: 0.72-1.32 mg/L

60-69 years: 0.77-1.42 mg/L

70-79 years: 0.82-1.52 mg/L

>79 years: no reference values established

Females:

0 days-22 years: no reference values established

23-29 years: 0.57-0.90 mg/L

30-39 years: 0.59-0.98 mg/L

40-49 years: 0.62-1.07 mg/L

50-59 years: 0.64-1.17 mg/L

60-69 years: 0.66-1.26 mg/L

70-80 years: 0.68-1.36 mg/L

81-86 years: 0.70-1.45 mg/L

>86 years: no reference values established

 

eGFR

>60 mL/min/BSA

eGFR will not be calculated for patients under 18 years.

Cautions

Cystatin C:

Lipemic or frozen specimens, which become turbid after thawing, may interfere with the assay.

 

Estimated Glomerular Filtration Rate (eGFR):

eGFR is not a precise measure of GFR and can be influenced by nonrenal factors (eg, inflammation).

Day(s) Performed

24 hours per day, 7 days per week

Report Available

1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

82610

NY State Approved

Yes