Is serum hemoglobin level an independent prognostic factor for IgA nephropathy?: a systematic review and meta-analysis of observational cohort studies

Decreased serum hemoglobin (Hb) level is associated with Immunoglobulin A nephropathy (IgAN) progression. However, whether serum Hb level is an independent prognostic factor of IgAN remains controversial. Herein, we aimed to investigate the prognostic value of serum Hb level in IgAN. The Cochrane Library, Embase, PubMed and Open Grey databases were systematically searched and reviewed. Kidney disease progression of IgAN was defined as a doubling of serum creatinine (SCr), a 30% reduction in estimated glomerular filtration rate (eGFR), end-stage renal disease (ESRD), or death. We evaluated the hazard ratio (HR) between serum Hb level and the incidence of kidney disease progression in IgAN before and after adjusting for relevant covariates. We included nine studies with 10006 patients in the meta-analysis. As a continuous variable, we found that serum Hb was an independent prognostic factor of IgAN [unadjusted HR = 0.89, 95% confidence interval (CI) = 0.84–0.95, <i>I</i>² = 98%; adjusted HR = 0.85, 95% CI = 0.79–0.91, <i>I</i>² = 0%]. The sensitivity analysis confirmed the stability of these results. Consistently, as a dichotomous variable defined as the below/above cutoff for anemia, we observed a positive correlation between serum Hb and kidney disease progression in IgAN (unadjusted HR = 2.12, 95% CI = 1.44–3.12, <i>I</i>² = 79%; adjusted HR = 1.65, 95% CI = 1.20–2.27, <i>I</i>² = 0%). Serum Hb level was independently correlated with the incidence of kidney disease progression in IgAN.

血清血红蛋白（serum hemoglobin, Hb）水平降低与免疫球蛋白A肾病（Immunoglobulin A nephropathy, IgAN）的疾病进展相关，但血清Hb水平是否为IgAN的独立预后因素仍存在争议。本研究旨在探讨血清Hb水平在IgAN中的预后价值。我们系统检索并回顾了Cochrane图书馆、Embase、PubMed及Open Grey数据库。IgAN的肾脏疾病进展定义为血清肌酐（serum creatinine, SCr）翻倍、估算肾小球滤过率（estimated glomerular filtration rate, eGFR）下降30%、终末期肾病（end-stage renal disease, ESRD）或死亡。我们评估了校正相关协变量前后，血清Hb水平与IgAN患者肾脏疾病进展发生率之间的风险比（hazard ratio, HR）。本荟萃分析共纳入9项研究，涉及10006例患者。作为连续变量时，我们发现血清Hb是IgAN的独立预后因素[未校正HR=0.89，95%置信区间（confidence interval, CI）=0.84–0.95，I²=98%；校正后HR=0.85，95%CI=0.79–0.91，I²=0%]。敏感性分析证实了上述结果的稳定性。以贫血界值划分的二分变量分析结果一致，我们观察到血清Hb与IgAN患者肾脏疾病进展呈正相关（未校正HR=2.12，95%CI=1.44–3.12，I²=79%；校正后HR=1.65，95%CI=1.20–2.27，I²=0%）。综上，血清Hb水平与IgAN患者肾脏疾病进展的发生率独立相关。