Iron Status, Anemia, and Functional Capacity in Adults with Congenital Heart Disease

<b>Background:</b> Congenital heart disease (CHD) affects approximately 9 per 1000 live births worldwide, with increasing prevalence due to improved survival. Today, over 90% of individuals with CHD reach adulthood, resulting in a growing population of adults with congenital heart disease (ACHD). Despite its clinical relevance, iron deficiency (ID) and anemia have been insufficiently studied in this group. <b>Objectives:</b> To evaluate the prevalence and clinical impact of iron deficiency and anemia in ACHD, particularly their relationship with exercise capacity. <b>Methods:</b> We retrospectively analyzed 310 ACHD patients at University Hospital Düsseldorf between January 2017 and January 2019. Iron status was assessed using serum ferritin, transferrin saturation (TSAT), and hemoglobin levels. Exercise capacity was measured by cardiopulmonary exercise testing (VO₂ max). Prevalence and clinical associations were compared with those reported in heart failure populations, using ESC guideline criteria. Analyses were adjusted for age, sex, and defect complexity. <b>Results:</b> Iron deficiency (ID) was present in 183 patients (59.0%). Anemia was observed in 13 patients (4.2%), with 6 (46.2%) classified as microcytic and 5 (38.5%) as normocytic. Reduced exercise capacity, defined as VO₂ max <80% of predicted, was present in 51 patients (16.5%), occurring more frequently in those with complex CHD (31.3% vs. 11.3%, <i>p</i> < 0.001). ID was associated with a trend toward lower VO₂ max (21.3 vs. 23.5 mL/min/kg, <i>p</i> = 0.068), while anemia correlated with significantly reduced performance (19.8 ± 4.1 vs. 22.9 ± 6.3 mL/min/kg, <i>p</i> = 0.041). <b>Conclusions:</b> Iron deficiency is highly prevalent, and anemia-though less common-was consistently associated with reduced functional capacity in ACHD. These findings highlight the need for targeted screening and management strategies in this growing patient population.