18 Jan FAQ: Cystatin C
Cystatin C is a superior Glomerular Filtration Rate (GFR) marker for the diagnosis and therapeutic control of renal function for patients of all ages. The low molecular weight protein is produced at a constant rate in nearly every nucleated cell in the human body . It is freely filtered through a normal Glomerular membrane, and it is then reabsorbed and almost entirely catabolised in the proximal tubules. Hence, the Cystatin C concentration in human blood is closely related to GFR .
Why can Cystatin C provide an estimate of Glomerular Filtration Rate (GFR)?
Cystatin C is a potent cysteine proteinase inhibitor produced at a constant rate by all nucleated cells. Cystatin C is filtered effectively by the glomerulus, and then fully reabsorbed and broken down by the renal tubules for recycling. A raised level of serum Cystatin C correlates closely with GFR and is therefore a good indicator of reduced kidney function.
What is the advantage of using Cystatin C for GFR estimation compared to creatinine?
Creatinine values are dependent on variables including age and body mass and you must correct for this in calculating GFR. Cystatin C GFR gives a direct and accurate measurement of GFR independent of age and muscle mass.
What is the “creatinine-blind area”?
Serum creatinine values are not a direct measure of GFR. GFR can be reduced by as much as 50% while the serum creatinine value is still within the normal range – this is the “creatinine-blind area”.
Does Cystatin C GFR have a blind area?
Cystatin C does not have a blind area and gives an immediate and true measurement of GFR.
How does Cystatin GFR compare to gold standards for precise determination of GFR?
Gold standard methods include the use of intravenous injections of radio labelled substances such as Cr-51-EDTA and Tc-99m-DTPA, or iodinated agents such as iohexol. GFR determined as Cystatin C GFR shows a direct relationship between the reciprocal of Cystatin C concentration in serum/plasma and GFR. Correlation is very good and is not hampered by collection errors or errors introduced by multiple measurements of blood or urine samples.
What is the advantage of using Cystatin C to estimate GFR compared to gold standard methods for determination of GFR?
The Gentian Cystatin C analysis can be carried out on one routine blood samples, which can conveniently be done together with other standard tests in clinical analysers. Patients do not have to be invaded specifically for the Gentian Cystatin C test. More importantly, Gentian Cystatin C can replace a range of unpleasant tests, including urine collection or radioactive measurements with repeated blood sampling. Especially for paediatricians, Cystatin GFR is the preferred test method.
How can we get access to the Gentian Cystatin C GFR test?
Please contact email@example.com for information on how to access the Gentian Cystatin C GFR test in your country.
Is Gentian Cystatin C assay available on all clinical chemistry analysers?
The Gentian Cystatin C assay is available on most major clinical analyser. Please contact firstname.lastname@example.org for more information on availability on the clinical analyser in your laboratory.
Is Gentian Cystatin C assay standardised?
The Gentian Cystatin C assay is standardised to the international reference material ERM-DA471/IFCC, and has been repeatedly proven to be aligned with the world standards for Cystatin C measurement.
Is Gentian Cystatin C assay FDA510(k)-cleared?
Yes, the Gentian Cystatin C Immunoassay is FDA510(k) cleared and CE-marked.
- Abrahamson M et al: Biochem J 1990;268:287-94.
- Laterza OF et al: Clin Chem 2002;48:63-99.