DaVita Inc, Denver, CO, USA.
Am J Kidney Dis. 2010 Sep;56(3):540-6. doi: 10.1053/j.ajkd.2010.05.009. Epub 2010 Jul 16.
To make informed decisions in dosing erythropoiesis-stimulating agents and intravenous iron therapy, clinicians must determine whether differences between current and previous test results for anemia and iron status markers reflect expected variation, a significant change, or an actual trend.
Prospective observational cohort study.
SETTING & PARTICIPANTS: 30 patients undergoing thrice-weekly in-center hemodialysis.
Within-patient biological variations in hemoglobin (Hb) level, hematocrit (Hct), reticulocyte Hb content, transferrin saturation (TSAT), and ferritin level were determined over 12 consecutive treatment days.
OUTCOMES & MEASUREMENTS: We separately measured same-sample analytical variation and within-patient biological variation (coefficient of variation), then calculated the number of sampling days needed to determine the true or homeostatic value for each analyte with 95% probability. We also evaluated whether results differed among the first, second, and third dialysis days of the week.
Biological variation differed by analyte. Hb level (4.0%), Hct (4.0%), and reticulocyte Hb content (4.8%) showed much lower variation than TSAT (38.2%) or ferritin level (15.1%). Analytical variation ranged from 2.0%-6.9% for all analytes. We found that one sample day would be sufficient to establish the true mean Hb level or Hct within a level of closeness+/-20% and 95% probability. For the same levels of closeness and probability, one sample day would be needed for reticulocyte Hb content, 15 for TSAT, and 3 for ferritin level. No pairwise comparison for any of the 5 analytes yielded a significant difference between results obtained on the first, second, or third dialysis day of the week.
These findings may not apply to other patient populations.
Low biological variation renders Hb level, Hct, and reticulocyte Hb content, but not TSAT and ferritin level, suitable for trend analysis using results from 2 successive samples. TSAT and ferritin test results, unlike reticulocyte Hb content, have limited value in evaluating changes in iron status within individual hemodialysis patients.
为了在给予促红细胞生成素刺激剂和静脉铁剂治疗时做出明智决策，临床医生必须确定当前和以前的贫血和铁状态标志物检测结果之间的差异是反映预期变化、显著变化还是实际趋势。
前瞻性观察队列研究。
30 名接受每周三次中心血液透析的患者。
在 12 个连续治疗日内，分别测定血红蛋白（Hb）水平、血细胞比容（Hct）、网织红细胞 Hb 含量、转铁蛋白饱和度（TSAT）和铁蛋白水平的个体内生物学变异。
我们分别测量了同一样本的分析变异和个体内生物学变异（变异系数），然后计算了每个分析物需要多少个采样日才能以 95%的概率确定真实或体内平衡值。我们还评估了结果在一周的第一天、第二天和第三天是否不同。
生物学变异因分析物而异。Hb 水平（4.0%）、Hct（4.0%）和网织红细胞 Hb 含量（4.8%）的变异明显低于 TSAT（38.2%）或铁蛋白水平（15.1%）。所有分析物的分析变异范围为 2.0%-6.9%。我们发现，一个样本日足以在+/-20%的接近度和 95%的概率内确定真实的 Hb 水平或 Hct 均值。在相同的接近度和概率水平下，一个样本日就可以确定网织红细胞 Hb 含量，15 个样本日可以确定 TSAT，3 个样本日可以确定铁蛋白水平。对于这 5 种分析物中的任何一种，没有任何两两比较在每周第一天、第二天或第三天的结果之间产生显著差异。
这些发现可能不适用于其他患者人群。
低生物学变异使 Hb 水平、Hct 和网织红细胞 Hb 含量，但不是 TSAT 和铁蛋白水平，适合使用连续 2 个样本的结果进行趋势分析。与网织红细胞 Hb 含量不同，TSAT 和铁蛋白检测结果在评估个体血液透析患者铁状态变化方面价值有限。
