Supplementary Material for: Cognitive performance correlated with hemoglobin level in patients with chronic kidney disease: a data analysis from the National Health and Nutrition Examination Survey (NHANES) 2011- 2014

Introduction: Given the increased incidence of renal anemia and cognitive dysfunction in patients with chronic kidney disease (CKD), the association between hemoglobin levels and cognitive function in these patients remains elucidated. An optimal level of hemoglobin for the best cognitive performance in CKD has yet to be determined.
Methods: A retrospective cross-sectional study was conducted using data from 2011-2014 of the National Health and Nutrition Examination Survey (NHANES). Enrolled subjects for analysis were divided into the CKD and the non-CKD groups. The Animal Fluency Test (AF), Digit Symbol Substitution Test (DSST), Consortium to Establish a Registry for Alzheimer’s Disease Word Learning Test (CERAD-WL) and Word List Recall Test (CERAD-DR) were used to evaluate cognitive performances. We quantified the association between hemoglobin levels and cognitive function in patients with CKD and non-CKD subjects by using the logistic regression analysis. Plotted curves and inflection points were calculated by a recursive algorithm.
Results: The ratio of cognitive impairment was higher in the CKD group than in the non-CKD group. Hemoglobin levels were correlated with CERAD-DR and DSST in patients with CKD. For non-CKD subjects, the hemoglobin level was not correlated with any test results. The potential range of the hemoglobin level was 11.0 - 12.7 mg/dL for keeping better cognitive performance of patients with CKD.
Conclusion: Hemoglobin levels are associated with cognitive performance in patients with CKD. The treatment of renal anemia would be meaningful to reduce cognitive impairment in CKD.

Introduction: 鉴于慢性肾脏病（chronic kidney disease, CKD）患者肾性贫血（renal anemia）与认知功能障碍的发病率逐年升高，此类患者的血红蛋白（hemoglobin）水平与认知功能之间的关联仍有待阐明，且针对慢性肾脏病患者实现最优认知表现的理想血红蛋白水平亦尚未明确。
Methods: 本研究采用2011-2014年美国国家健康与营养调查（National Health and Nutrition Examination Survey, NHANES）的数据，开展了一项回顾性横断面研究。纳入分析的研究对象被分为慢性肾脏病组与非慢性肾脏病组。本研究采用动物流畅性测试（Animal Fluency Test, AF）、数字符号替换测试（Digit Symbol Substitution Test, DSST）、阿尔茨海默病登记联盟词汇学习测试（Consortium to Establish a Registry for Alzheimer’s Disease Word Learning Test, CERAD-WL）以及词汇列表回忆测试（Word List Recall Test, CERAD-DR）评估受试者的认知表现。通过logistic回归分析（logistic regression analysis），量化分析了慢性肾脏病患者与非慢性肾脏病受试者的血红蛋白水平与认知功能之间的关联。采用递归算法（recursive algorithm）计算绘制曲线与拐点。
Results: 慢性肾脏病组的认知功能障碍发生率高于非慢性肾脏病组。慢性肾脏病患者的血红蛋白水平与CERAD-DR及DSST测试结果存在相关性。而非慢性肾脏病受试者的血红蛋白水平与各项测试结果均无相关性。若慢性肾脏病患者要维持较佳的认知表现，其血红蛋白水平的适宜范围为11.0~12.7 mg/dL。
Conclusion: 慢性肾脏病患者的血红蛋白水平与认知表现存在相关性。针对肾性贫血的治疗对于降低慢性肾脏病患者的认知功能障碍风险具有重要意义。