Additionally, NICE recommended that whenever a request for serum cystatin C measurement is made, clinical laboratories should report an estimate of GFR using the CKD-EPI equation. Previous NICE guidance reviewed the evidence for cystatin C equations for adults and recommended that an eGFR measurement using cystatin C should be considered to confirm or rule out CKD in people with an eGFR (according to a creatinine-based equation) of 45-59 ml/min/1.73 m 2, sustained for at least 90 days, without proteinuria or other markers of kidney disease. Cystatin C is a 13 kDa cationic protein produced by all nucleated cells and plasma cystatin C concentrations are chiefly determined by GFR.
More recently, plasma cystatin-C has been introduced as an alternative endogenous marker. Various equations have been constructed that allow conversion of serum creatinine levels (sometimes along with demographic information such as age and sex) to GFR. Estimates of GFR can be obtained using serum creatinine, which is a universally available endogenous test of kidney function. However, gold standard methods of assessing GFR are technically demanding, expensive, time-consuming and unsuitable for widespread identification of CKD in the ‘at risk’ population. The gold standard methods of assessing GFR require measurement of an ideal filtration marker, typically using markers such inulin, 51Cr-EDTA, 99mTc-DTPA, 125I-iothalamate and iohexol. Knowledge of GFR is essential for the diagnosis and management of CKD, with a normal GFR being approximately 100 ml/min/1.73 m2.
The glomerular filtration rate (GFR) is equal to the sum of the filtration rates in all of the functioning nephrons and is the best index of overall kidney function.
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