Department for Internal Medicine IV-Nephrology and Hypertension, Saarland University Medical Center, Homburg, Germany, †Psychological Institute, Humboldt-Universität zu Berlin, Berlin, Germany.
Clin J Am Soc Nephrol. 2013 Oct;8(10):1764-72. doi: 10.2215/CJN.13021212. Epub 2013 Jul 11.
Plasma phosphate levels display considerable intraindividual variability. The phosphatonin fibroblast growth factor 23 is a central regulator of plasma phosphate levels, and it has been postulated to be a more stable marker than conventional CKD-mineral and bone disorder parameters. Thus, fibroblast growth factor 23 has been hypothesized to reflect time-averaged plasma phosphate levels in CKD patients.
DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Among 40 patients from the outpatient dialysis center, serial measurements of plasma calcium and phosphate (before every dialysis session) as well as C-terminal fibroblast growth factor 23, parathyroid hormone, and alkaline phosphatase (one time weekly) were performed over a study period of 4 weeks in November and December of 2011. Intraindividual variability of repeated plasma fibroblast growth factor 23 measurements compared with other CKD-mineral and bone disorder markers was tested, and the association of a single plasma fibroblast growth factor 23 measurement with time-averaged plasma phosphate levels was analyzed.
Against expectations, intraindividual variability of fibroblast growth factor 23 (median coefficient of variation=27%; interquartile range=20-35) was not lower than variability of plasma phosphate (median coefficient of variation=15%; interquartile range=10-20), parathyroid hormone (median coefficient of variation=24%; interquartile range=15-39), plasma calcium (median coefficient of variation=3%; interquartile range=2-4), or alkaline phosphatase (median coefficient of variation=5%; interquartile range=3-10). Moreover, the correlation between the last fibroblast growth factor 23 measurement after 4 weeks and time-averaged plasma phosphate did not surpass the correlation between the last fibroblast growth factor 23 measurement and a single plasma phosphate value (r=0.67, P<0.001; r=0.76, P<0.001, respectively).
Surprisingly, fibroblast growth factor 23 was not more closely associated to time-averaged plasma phosphate levels than a single plasma phosphate value, and it did not show a lower intraindividual variability than other tested markers of CKD-mineral and bone disorder. Thus, fibroblast growth factor 23 should not be used in clinical practice as a reflector of time-averaged plasma phosphate levels.
血浆磷酸盐水平表现出相当大的个体内变异性。成纤维细胞生长因子 23（fibroblast growth factor 23，FGF23）是血浆磷酸盐水平的核心调节剂，它被认为是比传统的慢性肾脏病矿物质和骨异常参数更稳定的标志物。因此，有人假设 FGF23 可以反映慢性肾脏病患者的平均血浆磷酸盐水平。
设计、地点、参与者和测量：在 2011 年 11 月至 12 月的 4 周研究期间，从门诊透析中心的 40 名患者中，连续测量了血浆钙和磷酸盐（每次透析前）以及 C 端 FGF23、甲状旁腺激素和碱性磷酸酶（每周一次）。检测了重复测量的血浆 FGF23 与其他慢性肾脏病矿物质和骨异常标志物的个体内变异性，并分析了单次血浆 FGF23 测量与平均血浆磷酸盐水平的相关性。
出乎意料的是，FGF23 的个体内变异性（中位数变异系数=27%；四分位距=20-35）并不低于血浆磷酸盐（中位数变异系数=15%；四分位距=10-20）、甲状旁腺激素（中位数变异系数=24%；四分位距=15-39）、血浆钙（中位数变异系数=3%；四分位距=2-4）或碱性磷酸酶（中位数变异系数=5%；四分位距=3-10）。此外，4 周后最后一次 FGF23 测量与平均血浆磷酸盐之间的相关性并不超过最后一次 FGF23 测量与单次血浆磷酸盐值之间的相关性（r=0.67，P<0.001；r=0.76，P<0.001）。
令人惊讶的是，FGF23 与平均血浆磷酸盐水平的相关性并不优于单次血浆磷酸盐值，而且它的个体内变异性并不低于其他测试的慢性肾脏病矿物质和骨异常标志物。因此，FGF23 不应在临床实践中用作平均血浆磷酸盐水平的反映物。
