Iron deficiency in pulmonary arterial hypertension: a matter of definition!
Background: There is increasing interest in the role of iron homeostasis in the natural history of pulmonary arterial hypertension (PAH). In our study we describe a work-up of iron status in a heterogeneous "real-life" PAH cohort according to different definitions of iron deficiency (ID).
Material and methods: In a retrospective study in 84 patients with PAH the presence of ID was assessed according to four different definitions: (1) soluble transferrin receptor (sTfR) > 2.07 mg/l, (2) ferritin < 30ug/l and transferrin saturation < 15%, (3) ferritin < 100ug/l and transferrin saturation < 20% and (4) an elevated ferritin-index (sTfR)/logFerritin dependent on CRP, respectively. Iron data were related to 6MWD, NYHA class, duration of disease, hemodynamic measurements, hemoglobin level (gender dependent), NT-proBNP, gender and to ABG values.
Results:All PAH patients (100%) displayed an elevated sTfR value. According to definition (2) 90.1% were iron sufficient and 9.9% were iron deficient. The criteria for ID in (3) displayed 63% of PAH patients to be iron sufficient, whereas 37.0% were iron deficient. The CRP dependent ferritin index (4) revealed 61,7% patients with normal iron status and 38,3% showed ID.
In (2), gender (p = 0,008) differed between the two groups. Definition (3) showed a significant difference in 6MWD (p = 0.005), NYHA class (p = 0.047), PVR (p = 0.009) and gender (p = 0,046). According to the Ferritin-Index (4), NYHA functional class (p = 0,018), anemia (men) (p = 0,010) and NT-proBNP (p = 0.016) differed between the groups.
Discussion:The diagnostic analyses of iron status in our cohort of PAH patients shows pronounced differences in frequencies of ID depending on its definition. This observation has to be taken into account when interpreting the results of individual patients. It is still unclear whether ID has a causal relationship to PAH or is an epiphenomenon. The issue of the most suitable definition of ID in PAH further complicates the selection of appropriate patients for iron supplementation.