Sjöström P, Tidman M, Jones I
Department of Medicine, Orebro University Hospital, Orebro, Sweden.
Scand J Clin Lab Invest. 2005;65(2):111-24. doi: 10.1080/00365510510013523.
Cystatin C has been proposed as an endogenous marker for measuring glomerular filtration rate (GFR) and is regarded as being equivalent to or better than creatinine. However, there are no published data on the production rate (Cys(pr)) or on the non-renal clearance of cystatin C (CL(nr)) in humans, which are essential parameters for GFR calculation. GFR was determined by measuring the plasma clearance of iohexol. Cystatin C, creatinine, urea and albumin were determined on the same serum samples as iohexol; 381 patients with a GFR range of 12-151 ml/min/1.73 m2, and 70 patients on haemodialysis were evaluated. Renal clearance of cystatin C (CLr) equals GFR * S (the sieving coefficient). Plasma clearance (CL) = CLr + CLnr. The relationship between Cys(pr) and the elimination rate (CL * serum-cystatin C) can be expressed as Cys(pr) = (S * GFR+CLnr) * serum-cystatin C. Assuming that the unknown values of Cys(pr) and CLnr are independent of GFR, the equation can be solved from GFR (iohexol clearance) and serum cystatin C (s-Cys) patient data. For S=1, we found Cys(pr) = 0.124 +/- 0.023 mg/min/1.73 m2 and Cl(nr)=22.3 ml/min/1.73 m2. For S = 0.94, found in rats, the values will be Cys(pr) = 0.117 mg/min/1.73 m2 and Cl(nr) = 21 ml/min/1.73 m2 and S-Cys in 70 patients on chronic haemodialysis was found to be 5.74 +/- 1.15 mg/l, in agreement with a calculated value of 5.56 mg/l (s-Cys=124/22.3) for GFR=zero. The mean value of the calculated Cl(nr) for the 70 patients was 22.7 +/- 6.6 ml/min/1.73 m2, which confirms the calculated level and indicates its biological variation. We thus propose the following formula for calculating GFR using the values found for CLnr and Cys(pr) in this study: GFR=124/s - Cys - 22.3 ml/min/1.73 m2, where serum cystatin C concentration is given as mg/l.
胱抑素C已被提议作为测量肾小球滤过率（GFR）的内源性标志物，并且被认为等同于肌酐或比肌酐更好。然而，关于人体中胱抑素C的产生率（Cys(pr)）或非肾清除率（CL(nr)）尚无公开数据，而这两个参数是计算GFR所必需的。通过测量碘海醇的血浆清除率来测定GFR。在与碘海醇相同的血清样本中测定胱抑素C、肌酐、尿素和白蛋白；评估了381例GFR范围为12 - 151 ml/min/1.73 m²的患者以及70例接受血液透析的患者。胱抑素C的肾清除率（CLr）等于GFR * S（筛滤系数）。血浆清除率（CL）= CLr + CLnr。Cys(pr)与清除率（CL * 血清胱抑素C）之间的关系可表示为Cys(pr) = (S * GFR + CLnr) * 血清胱抑素C。假设Cys(pr)和CLnr的未知值与GFR无关，则可根据GFR（碘海醇清除率）和血清胱抑素C（s - Cys）患者数据求解该方程。对于S = 1，我们发现Cys(pr) = 0.124 ± 0.023 mg/min/1.73 m²且Cl(nr) = 22.3 ml/min/1.73 m²。对于在大鼠中发现的S = 0.94，其值将为Cys(pr) = 0.117 mg/min/1.73 m²且Cl(nr) = 21 ml/min/1.73 m²，并且发现70例慢性血液透析患者的S - Cys为5.74 ± 1.15 mg/l，与GFR = 零时计算值5.56 mg/l（s - Cys = 124/22.3）一致。70例患者计算出的Cl(nr)平均值为22.7 ± 6.6 ml/min/1.73 m²，这证实了计算水平并表明了其生物学变异。因此，我们提出以下使用本研究中发现的CLnr和Cys(pr)值来计算GFR的公式：GFR = 124/s - Cys - 22.3 ml/min/1.73 m²，其中血清胱抑素C浓度以mg/l为单位。
