My almost 4 month old recently had a blood test that showed low iron. The doctor said because a few other things they checked were fine that he doesn’t need to have an iron supplement.

My question is how can this be happening? He was combi fed previously but is now just formula fed. The doctor said it’s very unusual to see a formula fed baby have low iron. Could it be my previous breastfeeding caused the low iron (dr said low iron is more common in breastfed babies) and it just hasn’t recovered yet? I’m uk based so if I want to speak to a doctor it will have to just be the family GP.

Edited: They checked his levels as part of an assessment for possible sleep apnea.