Iron is a biologically essential micronutrient. Iron deficiency alters erythropoiesis and is considered as a major cause of disability worldwide. Interestingly, iron overload is never observed in cystic fibrosis contrarily to others chronic respiratory diseases. Moreover, iron deficiency reported prevalence in CF is very high (up to 60% in retrospective series) and is correlated to an alteration of respiratory function.

Cystic fibrosis patients should be tested annually for iron deficiency. Serum ferritin is the best diagnosis tool for iron deficiency (specificity 87% for a threshold < 30 µg/L). Previously published studies used less performant markers such as serum iron (< 12 µmol/L) or transferrin saturation (< 12%), which are markedly influenced by the systemic inflammation. CF patients experiences frequent pulmonary exacerbations leading to systemic inflammation: iron stores should therefore be assessed at optimal time with no inflammation.

The I-MUCO study aims to determine the exact prevalence of iron deficiency in CF patients. We aimed to identify risk factors for iron deficiency onset.

Inclusion Criteria:

• Cystic fibrosis genetically proven.
• Age ≥ 18 years
• Systematic annual follow-up.

Exclusion Criteria:

• Dietary or drugs iron supplements
• Systemic inflammation or pulmonary exacerbation
• Lung transplantation

consecutive patients followed at the referral center for cystic fibrosis of Lyon (France).