CYSTATIN C - Recommended for assessment of GFR and kidney function
06. May 2022 |
8 min read
Analysing cystatin C and creatinine together can give the physician more accurate information on the patient’s eGFR than creatinine alone.The National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) has, in a joint taskforce, recently recommended increasing the use of cystatin C combined with serum (blood) creatinine, as a confirmatory assessment of GFR or kidney function to secure unbiased diagnostics.
A better estimated Glomerular Filtration Rate (eGFR)1-2
While the clinical use of cystatin C can have far-reaching benefits across all patient groups, certain vulnerable patient populations may experience a greater benefit. Specifically, children, amputees and the elderly can receive more accurate eGFRs with cystatin C, since cystatin C is less susceptible to factors that affect muscle mass, like age, diet, sex, race, physical activity, etc.3,4.
Clinical use of cystatin C is recommended in guidelines published by KDIGO5. The National Kidney Foundation (NKF) in the US and the American Society of Nephrology (ASN) have also recently, in a joint taskforce, recommended to increase the use of cystatin C combined with serum (blood) creatinine as a confirmatory assessment of GFR or kidney function6.
Removing the race factor from creatinine equations
The NKF-ASN task force also suggests removing the race factor from the creatinine equations3. The removal of the race factor introduces systematic misclassification that cannot be eliminated even when numerous non-GFR determinants of the serum creatinine level are accounted for7. Cystatin C based eGFR equations are without a race factor and cystatin C can be used together with creatinine, or on its own, to calculate the eGFR without the race factor. The most accurate results will be with the combination of cystatin C and creatinine8.
The ideal combination with creatinine
Serum creatinine levels are only elevated after about 50% of renal function is lost9. This insensitivity to mild renal insufficiency within what is known as the creatinine blind area (30-70 ml/min/1.73 m2) could give a false sense of security that in-tern leads to under diagnosis of chronic kidney disease (CKD) stages 1 and 2. Depending on creatinine alone to assess kidney function may therefore prevent detection of a variety of renal diseases for which early treatment is critical10.
GFR estimating equations that incorporate both creatinine and cystatin C values together are more accurate than equations that use either marker alone7,11. Using cystatin C in conjunction with creatinine to risk stratify CKD patients can allow for better allocation resources such as nephrology referrals, medication dosage adjustments and more invasive kidney function tests12. Use of cystatin C in combination with creatinine has also been shown to strengthen the association between eGFR and risk of cardiovascular disease, progression into end-stage renal disease and death13.
Cystatin C with stronger correlation with mGFR:
The graphs to the left illustrate the stronger correlation observed between cystatin C serum concentrations and iohexol clearance rates relative to that which is seen with creatinine. This improved correlation can be of clinical significance and lead to improved patient care14.
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