Background: Urinary excretion of the low molecular weight protein
cystatin C is a marker of renal disorders and a good predictor of the severity of
acute tubular necrosis. We evaluated the measurement of urinary cystatin C and
determined its reference range.
Methods: Measurement of urinary cystatin C by particle-enhanced
nephelometric immunoassay (PENIA) in 102 patients with various renal disorders and
133 healthy controls. We assessed the influence of pH and temperature, interferences
on urinary cystatin C measurement, as well as cystatin C adsorption to plastic.
Results: The upper reference value for urinary cystatin C was 0.28 mg/L,
independent of age and gender. Accuracy and linearity (r
2=0.996) were excellent. Intra- and inter-assay precision were ≤4.8% and
≤5.2%, respectively. Albumin (≤160 g/L), bilirubin (≤500 µmol/L) and
haemoglobin (≤210 µmol/L) did not show interferences. Urinary
cystatin C was stable, at urine pH≥5, at -20°C and 4°C for 7 days, and at 20°C for 48
h. Freezing and thawing did not influence urinary cystatin C concentration. There was
no adsorption of cystatin C to plastic.
Conclusion: Urinary cystatin C measurement by PENIA is precise. High
stability and no interference add to the practicability of urinary cystatin C as a
routine biochemical test.
