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Cystatin C – Serum Blood Test

The protease cystatin C is a protein with 120 amino acids, which is relatively constantly produced in nucleated body cells (housekeeping gene). The elimination is done exclusively by glomerular filtration.

Standard value:

0,53–0,95 mg/l, higher concentrations in children under the age of 1.

Laboratory test method:

Immunoturbidimetry: cystatin C and specific antibodies form antigen-antibody complexes which can be optically detected by a photometer (measurement of the resulting specific turbidity).

Indications:

Early diagnosis of renal dysfunction, to estimate renal clearance without the need for urine collection.

Differential Diagnosis of Elevated Cystatin C

• Acute kidney injury and chronic kidney disease. Cystatin C is more sensitive than creatinine to detect mild kidney damage (40–80 ml/min GFR).
• The concentration of cystatin C is independent of age, weight, muscle mass and diet.
• Non-renal causes of cystatin C elevation are autoimmune diseases.

Calculation of the Glomerular Filtration Rate (GRF)

The following formula can estimate the glomerular filtration rate with the serum concentration of cystatin C (Larsson u.a., 2004):

GFR = 77,24 × (Cystatin C in mg/l)^−1,26

References

  Deutsche Version: Cystatin C Laborwert