Anemia Prevalence, Type, and Associated Risks in a Cohort of 5.0 Million Insured Patients in the United States by Level of Kidney Function

Rationale & Objective: Anemia is common in chronic kidney disease (CKD); although anemia is associated with adverse outcomes, the avail-able treatments are not ideal. We characterized the burden, risk factors for, and risks associated with anemia by estimated glomerular filtration rate (eGFR) and hemoglobin level.Study Design: Cross-sectional and prospective cohort study.Setting & Participants: Outpatient data from 5,004,957 individuals across 57 health care centers in the United States from 2016 to 2019, extracted from the Optum Labs Data Warehouse.Exposure: Severity of anemia, presence of low iron test results, eGFR. Outcome: Incident kidney failure with replace-ment therapy, cardiovascular disease, coronary heart disease, stroke, heart failure, death.Analytical Approach: The prevalences of anemia, low iron test results, vitamin B12 deficiency, and erythropoiesis-stimulating agent (ESA) use, stratified by sex and eGFR, were characterized. Polychotomous logistic regression was used to estimate the adjusted odds ratios of different hemoglobin levels across eGFR. Cox proportional hazards regression was used to calculate adjusted hazard ratios for adverse outcomes across hemoglobin level.Results: The mean age was 54 years, and 42% were male. Lower eGFR was very strongly associated with increased prevalence of anemia, even after adjustment. Although iron studies were checked infrequently in patients with anemia, low iron test results were highly prevalent in those tested: 60.4% and 81.3% of men and women, respectively. ESA use was uncommon, with a prevalence of use of <4%. Lower hemoglobin was independently associated with increased risk of incident kidney failure with replacement ther-apy, cardiovascular disease, coronary heart dis-ease, stroke, heart failure, and death.Limitations: Reliance on ICD codes for medical diagnoses, death information obtained from claims data, observational study. Conclusions: Severe anemia was common and strongly associated with lower eGFR and multiple adverse outcomes. Low-iron test results were highly prevalent in those tested despite iron studies being checked infrequently. ESA use in nondialysis CKD patients was uncommon.