Cystatin C eGFR


Abbrev Code:CYSGFR   
Order Code:LAB3417Order Name:Cystatin C with GFR
Synonyms:Cystatin C; Cystatin-C with CKD-EPI Calculation; Glomerular Filtration Rate, GFR
Methodology:Particle enhanced immunoturbidmetric assay
CPT Codes: 82610 x1, 82610 x1
Turnaround Time:Performed and reported 24 hours/day.
Associated Links:

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Collection Instructions

Specimen:Blood
Optimal Volume:2 mL
Minimum\Peds Volume:1 mL
Container:Green (lithium heparin, gel)
Alternate Containers: Green (lithium heparin, gel) on ICE, Green (sodium heparin, no gel), Red (no gel), Red or gold (gel)
Causes for Rejection:Grossly hemolyzed specimens.


Processing and Shipping

Specimen Processing:Cenrifuge and aliquot 0.5 mL, 0.4 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Test Performed at or Referral Lab (Roche-UMMC East)


Interpretive

Reference Range:Roche: 2.5-97.5%. 0.61 mg/L to 0.95 mg/L
Limitations:Limitations:
  •  It has been reported that cystatin C serum concentrations are not affected by standardized high-dose corticosteroid therapy but may be increased in patients with impaired renal function receiving corticosteroids.
  • Cystatin C is sensitive to changes in thyroid function and should not be used without knowledge of thyroid status.
  • Icterus: No significant interference up to 60 mg/dL bilirubin.
  • Hemolysis: No significant interference up to 1000 mg/dL hemoglobin.
  • Lipemia (Intralipid):28 No significant interference up to an L index of 1000. There is poor correlation between the L index (corresponds to turbidity) and triglycerides concentration.
  • Rheumatoid factors: No significant interference from rheumatoid factors up to a concentration of 1200 IU/mL.
  • High-dose hook effect: No false result occurs up to a cystatin C concentration of 12 mg/L.
  • Drugs: No interference was found at therapeutic concentrations using common drug panels.
  • In very rare cases, gammopathy, in particular type IgM (Waldenström’s macroglobulinemia), may cause unreliable results.
  • In very rare cases falsely elevated results for cystatin C will be obtained from samples taken from patients who have been treated with rabbit antibodies or have developed anti‑rabbit antibodies.

References available on request. For diagnostic purposes, the results should always be assessed in conjunction with the patient’s medical history, clinical examination and other findings.
Use:Chronic kidney disease is a worldwide health problem that carries a substantial risk for cardiovascular morbidity and death. Current guidelines define chronic kidney disease as kidney damage or glomerular filtration rate (GFR) less than 60 mL/min per 1.73 m2 for 3 months or more, regardless of cause. GFR is the most frequently used criteria in the assessment of renal function. Serum creatinine as an estimation of GFR is not ideal because it is significantly changed by other factors such as muscle mass, diet, gender, age and tubular secretion.

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. There is a small dependency of cystatin C concentration from age in the age range 1 to 50 years, whereas the cystatin C concentration of healthy individuals >50 years increases with age. Therefore, cystatin C in plasma and serum has been proposed as a more sensitive marker for GFR in children and adults, 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.

As with creatinine, several cystatin C based prediction equations for calculation of GFR in adults and children have been published. It should be noted that these formulas were evaluated with different cystatin c assays (particle-enhanced nephelometric immunoassay PENIA or particle enhanced turbidimetric immunoassay (PETIA) and may reveal inaccurate GFR results if an inappropriate combination of formula is used.


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