Background: Iron deficiency affects up to 50% of patients with pulmonary arterial hypertension (PAH) but iron markers such as ferritin and serum iron are confounded by several non-disease related factors like acute inflammation and diet. The aim of this study was to identify a new marker for iron deficiency and clinical outcome in PAH patients.

Methods: In this single-center, retrospective study we assessed indicators of iron status and clinical parameters specifying the time to clinical worsening (TTCW) and survival in PAH patients at time of initial diagnosis and at 1-year follow-up using univariable and multivariable analysis.

Results: In total, 150 patients were included with an invasively confirmed PAH and complete data on iron metabolism. The proportion of hypochromic erythrocytes >2% at initial diagnosis was identified as an independent predictor for a shorter TTCW (p=0.0001) and worse survival (p=0.002) at initial diagnosis as well as worse survival (p=0.016) at 1-year follow-up. Only a subset of these patients (64%) suffered from iron deficiency. Low ferritin or low serum iron neither correlated with TTCW nor survival. Severe hemoglobin deficiency at baseline was significantly associated with a shorter TTCW (p=0.001).

Conclusions: The presence of hypochromic erythrocytes >2% was a strong and independent predictor of mortality and shorter TTCW in this cohort of PAH patients. Thus, it can serve as a valuable indicator of iron homeostasis and prognosis even in patients without iron deficiency or anemia. Further studies are needed to confirm the results and to investigate therapeutic implications.