University of Rochester Medical Center, Box 777, 601 Elmwood Avenue, Rochester, NY, USA.
Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
Pediatr Nephrol. 2020 Feb;35(2):279-285. doi: 10.1007/s00467-019-04389-2. Epub 2019 Nov 3.
Cystatin C is a key GFR biomarker. Recently, Siemens recalibrated the assay based on certified reference material ERM-DA471/IFCC. The NIH-funded longitudinal chronic kidney disease in children (CKiD) study has > 3000 cystatin C measurements based on a pre-IFCC calibrator provided by Siemens. Since cystatin C values for CKiD are now standardized to IFCC certified reference material, it is important to relate the IFCC-calibrated results to the previous values so that there are no discontinuous results.
We diluted cystatin C ERM-DA471/IFCC (5.48 mg/L) into buffer and compared results with predicted ones. We then updated the cystatin C application on our BN II nephelometer to provide results based on pre-IFCC and IFCC calibrations of CKiD specimens simultaneously. We assayed 51 previously analyzed sera and 62 fresh additional specimens.
The predicted concentrations from the IFCC standard were consistently 17% higher than the measured values using the pre-IFCC calibration (y = 1.1686x). Similarly, the re-run and fresh sample concentrations were 17% higher via the IFCC calibration than by the pre-IFCC calibration (y = 1.168x). There was very high reliability in the measurements using the previous calibration for re-run specimens (0.99) and for 33 pristine specimens using IFCC calibration (0.99).
We confirm the recalibration proposed by Siemens. To convert pre-IFCC results to IFCC-calibrated concentrations, the value is multiplied by 1.17. Conversely, one divides IFCC-calibrated results by 1.17 to estimate GFR via previously published pre-IFCC CKiD eGFR equations. For older adolescents, cystatin C has already been standardized and can be directly applied to the CKD-EPI equations.
半胱氨酸蛋白酶抑制剂 C 是肾小球滤过率（GFR）的重要生物标志物。最近，西门子公司基于认证参考物质 ERM-DA471/IFCC 对该检测方法进行了重新校准。美国国立卫生研究院（NIH）资助的儿童慢性肾脏病纵向研究（CKiD）项目包含超过 3000 项基于西门子提供的预 IFCC 校准物的半胱氨酸蛋白酶抑制剂 C 测量值。由于 CKiD 的半胱氨酸蛋白酶抑制剂 C 值现在已标准化为 IFCC 认证参考物质，因此将 IFCC 校准结果与之前的值相关联非常重要，以免出现不连续的结果。
我们将 ERM-DA471/IFCC（5.48mg/L）半胱氨酸蛋白酶抑制剂 C 稀释至缓冲液中，并将结果与预测值进行比较。然后，我们更新了 BN II 散射浊度计上的半胱氨酸蛋白酶抑制剂 C 应用程序，以便同时提供基于 CKiD 标本预 IFCC 和 IFCC 校准的结果。我们检测了 51 份先前分析的血清和 62 份新鲜附加标本。
使用预 IFCC 校准测量时，IFCC 标准预测的浓度始终比实测值高 17%（y=1.1686x）。同样，使用 IFCC 校准的重新检测和新鲜样本浓度比使用预 IFCC 校准的浓度高 17%（y=1.168x）。使用之前的校准对重新检测的标本进行测量具有非常高的可靠性（0.99），对使用 IFCC 校准的 33 份原始标本进行测量也具有非常高的可靠性（0.99）。
我们证实了西门子公司提出的重新校准。要将预 IFCC 结果转换为 IFCC 校准浓度，将值乘以 1.17。相反，要通过之前发表的预 IFCC CKiD eGFR 方程估算 GFR，可以将 IFCC 校准的结果除以 1.17。对于年龄较大的青少年，半胱氨酸蛋白酶抑制剂 C 已经标准化，可以直接应用于 CKD-EPI 方程。
