CYSTATIN C - Recommended for assessment of GFR and kidney function

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 alone^7,11. 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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