Minneapolis Medical Research Foundation, MN, USA.
Am J Kidney Dis. 2011 Feb;57(2):255-65. doi: 10.1053/j.ajkd.2010.06.013.
Substantial variability in hemoglobin levels has been associated with increased mortality risk in hemodialysis patients. Variability also has been associated with concurrent comorbid conditions and hospitalization. Adequate adjustment for confounding by disease severity is needed to estimate the association of hemoglobin level variability with mortality risk.
Retrospective cohort study.
SETTING & PARTICIPANTS: Medicare hemodialysis patients in 3 groups: prevalent on July 1, 2006 (n = 133,246), prevalent on July 1, 1996 (n = 78,602), and incident between January 1, 2005, and June 30, 2006 (n = 24,999).
Hemoglobin level variability estimated using the residual deviation around the linear trend in hemoglobin levels during a 6-month entry period.
Time to death.
We fit Cox models of 1-year mortality with and without adjustment for disease severity (comorbid conditions, hospitalization days, and months with hemoglobin level <10 g/dL), measured concurrently with hemoglobin level variability.
Disease severity was associated positively with hemoglobin level variability in all groups. Before adjustment for disease severity, HRs for hemoglobin level variability were 1.27 (95% CI, 1.24-1.31) per 1 g/dL for patients prevalent in 2006, 1.32 (95% CI, 1.27-1.38) for patients prevalent in 1996, and 1.08 (95% CI, 1.03-1.13) for patients incident in 2005-2006. After adjustment, HRs for hemoglobin level variability were 1.02 (95% CI, 0.99-1.05), 1.07 (95% CI, 1.03-1.12), and 1.01 (95% CI, 0.95-1.06), respectively.
We did not adjust for time-varying confounding of hemoglobin level; an inclusion requirement introduces potential selection bias; our findings may not apply to incident hemodialysis patients younger than 65 years; assessment of comorbid conditions from claims is subject to misclassification, with possible residual confounding attributable to comorbid conditions; this observational study cannot prove causality.
After adjustment for concurrent disease severity, evidence supporting an association between hemoglobin level variability and mortality risk was weak and inconsistent. The clinical utility of hemoglobin level variability may be limited.
血红蛋白水平的显著变化与血液透析患者的死亡风险增加有关。变化也与并发合并症和住院有关。需要充分调整疾病严重程度的混杂因素，以估计血红蛋白水平变化与死亡风险的关联。
回顾性队列研究。
医疗保险血液透析患者分为三组：2006 年 7 月 1 日之前（n = 133246）、1996 年 7 月 1 日之前（n = 78602）和 2005 年 1 月 1 日至 2006 年 6 月 30 日之间的新发病例（n = 24999）。
血红蛋白水平变化，使用血红蛋白水平 6 个月入组期间线性趋势的剩余偏差来估计。
死亡时间。
我们拟合了伴有和不伴有疾病严重程度（合并症、住院天数和血红蛋白水平<10g/dL 的月份）调整的 1 年死亡率的 Cox 模型，同时测量了血红蛋白水平变化。
在所有组中，疾病严重程度与血红蛋白水平变化呈正相关。在没有调整疾病严重程度之前，2006 年之前的患者血红蛋白水平变化的 HR 为每 1g/dL 1.27（95%CI，1.24-1.31），1996 年之前的患者为 1.32（95%CI，1.27-1.38），2005-2006 年新发病例的患者为 1.08（95%CI，1.03-1.13）。调整后，血红蛋白水平变化的 HR 分别为 1.02（95%CI，0.99-1.05）、1.07（95%CI，1.03-1.12）和 1.01（95%CI，0.95-1.06）。
我们没有调整血红蛋白水平的时变混杂；纳入标准引入了潜在的选择偏倚；我们的研究结果可能不适用于 65 岁以下的新发病例；从索赔中评估合并症存在错误分类的可能性，可能存在归因于合并症的残留混杂；这种观察性研究不能证明因果关系。
在调整并发疾病严重程度后，支持血红蛋白水平变化与死亡风险之间存在关联的证据微弱且不一致。血红蛋白水平变化的临床实用性可能有限。
