Newly diagnosed iron deficiency anemia and subsequent autoimmune disease: a matched cohort study in Taiwan.

Objective: To explore whether newly diagnosed iron deficiency anemia (IDA) is associated with subsequent systemic autoimmune disease onset. Methods: The study identified 22,440 patients who received a diagnosis of IDA between 2000 and 2012 from a random sample of 1 million people from Taiwan's National Health Insurance Research Database. The patients with IDA were randomly matched with 89,528 patients with no IDA by age, gender, and index year. We followed the 2 groups until systemic autoimmune disease onset. Cox proportional hazards analysis was used to determine autoimmune disease risk by age, gender, and comorbidities, in terms of hazard ratios (HRs) and 95% confidence intervals (CIs). Results: Adjusted HR (95% CI) of autoimmune disease in the IDA group was 2.37 (1.92-2.92) compared with the non-IDA group. The subgroup analysis indicated that a patient with IDA had a significantly greater risk of an autoimmune disease if they were female or had the comorbidities of hypertension, hyperlipidemia, cancer, allergic rhinitis, urticaria, chronic obstructive pulmonary disease, or chronic liver disease. An autoimmune disease was significantly more likely to occur within 2 years after a new diagnosis of IDA. Conclusions: IDA significantly increases autoimmune disease risk, particularly in female patients and patients with certain comorbidities. Clinicians should conduct further clinical evaluations and laboratory tests of autoimmune disease in patients with IDA. Plain Language Summary: Little is known about the relationship between iron deficiency and autoimmune disease. By using a national-level database in Taiwan, we noted a meaningful association between iron deficiency anemia (IDA) and later autoimmune disease development. Our study extends the known disease range and recommends that physicians be alert for the occurrence of autoimmune disease after an IDA diagnosis. The subgroup analysis indicated that, among patients with IDA, female patients and patients with the simultaneous chronic diseases of allergic rhinitis, urticaria, cancer, chronic obstructive pulmonary disease (COPD), hyperlipidemia, or hypertension had a significantly higher risk of autoimmune disease. The risk of autoimmune disease was considerably higher within the 2 years after an IDA diagnosis.