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Nephrology 20 (2015) 383–385

Correspondence ELEVATED SERUM CREATININE IN A PATIENT WITH NORMAL RENAL FUNCTION: THE VALUE OF CYSTATIN C Sheena Sahota, Roger A Rodby and Stephen M Korbet, Division of Nephrology, Department of Medicine, Rush University Medical Center, Chicago, Illinois, USA

The serum creatinine has long been the basis for estimating glomerular filtration rate (eGFR). However, since serum creatinine is dependent on muscle mass, estimations of GFR based on the creatinine can be inaccurate in patients at extremes (high or low) of muscle mass. Cystatin C, another marker of GFR, is largely unaffected by muscle mass, and thus, using cystatin C alone or in combination with creatinine has been shown to be more accurate in determining eGFR than equations using the serum creatinine alone.1–3 We present a case of a muscular patient who was referred for evaluation of chronic kidney disease (CKD) based on a creatinine-based eGFR of 60 mL/min per 1.73 m2. The cystatin C and eGFRcys remained unchanged in the normal range. Cystatin C is a low molecular weight non-glycosylated protein (13 359 Da) which is synthesized by all nucleated cells at a constant rate, is freely filtered by the glomerulus, reabsorbed and catabolized in the proximal tubule, and does not appear in the urine. Unlike serum creatinine, cystatin C is not affected by muscle mass or diet.2,4,5 As a result, the use of the cystatin C level in estimating GFR either alone (eGFRcys) or in combination with creatinine (eGFRcreatcys) is now considered to be a more reliable measure of renal function, particularly in patients whose creatinine production may be unpredictable.2,4,5 Additionally, studies have shown that the use of cystatin C improves the accuracy eGFR measurements (eGFRcyst) and better correlates with outcomes such as ESRD and death than estimates using the serum creatinine (eGFRcreat).2 The recent study by Shlipak et al.,2 found that 42% of patients initially classified as CKD stage 3 using creatinine to calculate eGFR (eGFRcreat) were reclassified to an eGFR of >60 mL/min per 1.73 m2 when cystatin C was used to calculate the eGFR (alone or with creatinine). The patients reclassified to an eGFRcyst >60 mL/ min per 1.73 m2 had an improved prognosis with the risk of death reduced by 34% and the risk of ESRD reduced by 80% compared with those patients that continued to have a cystatin C eGFRcyst of

Elevated serum creatinine in a patient with normal renal function: the value of Cystatin C.

Elevated serum creatinine in a patient with normal renal function: the value of Cystatin C. - PDF Download Free
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