Iron Deficiency Anemia in an Active Crohn Flare: Choosing the Iron Route
A single patient, iron-deficient during an active Crohn flare. The disagreement isn't about whether she needs iron — it's about whether her own inflamed gut can be trusted to absorb it.
Renata O. manages the overnight shift at a wholesale bakery, a job built around the same three a.m. alarm she has kept for six years, and is seven months from a wedding she has been planning with her sister since before her Crohn disease was even diagnosed. She has ileocolonic Crohn disease, established four years ago, generally quiet on maintenance adalimumab — but for the past six weeks she has had increasing right lower quadrant cramping, four to five loose stools a day, and a fatigue heavy enough that she has started sitting down twice during a shift she used to work standing straight through. She attributed the tiredness to the wedding planning until her gastroenterologist's labs came back, and on exam she is visibly pale with mild right lower quadrant tenderness but no rebound or guarding — a flare, not a surgical abdomen.
Her hemoglobin is 9.4, down from a stable 12.8 eight months ago, with a low ferritin of 11 — unambiguous even though ferritin is also an acute-phase reactant, since a value this low cannot be explained away by inflammation the way a borderline-normal one sometimes can; true iron-replete inflammation typically holds ferritin well above 100, not near the floor of normal. Her CRP is 34, and a calprotectin drawn the same week is markedly elevated, confirming what her stool frequency already suggested: this is an active flare, not a quiet gut with an incidental anemia riding alongside it.
That timing is exactly what makes the iron-repletion route a genuine question rather than a formality. Active mucosal inflammation drives hepatic hepcidin production, which degrades ferroportin at the enterocyte's basolateral membrane and traps iron inside the gut lining rather than releasing it into her bloodstream — a mechanism that operates regardless of how much oral iron she swallows. Practically, that means an oral regimen dosed for a straightforward iron-deficient patient risks doing two things at once here: delivering little of its iron past her inflamed ileum, and leaving the unabsorbed fraction sitting in a bowel already producing four to five stools a day, a combination her gastroenterologist has seen worsen cramping in prior flares before it ever helped her hemoglobin.
Choosing the iron route mid-flare
Oral ferrous sulfate is the reflex reach in any other iron-deficient patient, but it is the wrong reflex here. Hepcidin rises with active inflammation and shuts down ferroportin at the enterocyte, so oral iron has real trouble getting past her gut wall right now regardless of dose — and the unabsorbed fraction sitting in an already-inflamed lumen is a plausible way to make her cramping and stool frequency worse, not better.
FERGIcor, the largest randomized comparison of IV ferric carboxymaltose against oral iron sulfate in IBD-associated anemia, found the IV arm reached its hemoglobin-response target faster and more reliably than oral iron — and, notably, that advantage held regardless of whether a patient's disease was clinically active or quiescent at enrollment. Her flare isn't a reason to hold IV iron; if anything it's the population where the oral route was already shown to underperform.
I don't disagree with the hepcidin mechanism, and I'm not going to argue for oral sulfate in an active flare. But ferric carboxymaltose carries a real, labeled risk of severe hypophosphatemia in patients getting repeated infusions, mediated through FGF23 induction — something worth naming before it becomes a second problem nobody was watching for, especially since her wedding is seven months out and a second round of infusions is a live possibility if this flare runs long.
A single point in her favor for tolerating it: her renal function is normal and this would be her first-ever iron infusion, so there's no accumulated phosphate-wasting history to worry about yet — just a baseline phosphate worth checking before and a few weeks after.
Agreed within the visit: ferric carboxymaltose dosed to her weight and hemoglobin deficit, given as a single infusion rather than split, with a baseline phosphate drawn the same day and a repeat at three weeks.
Not fully settled: whether a second infusion, if her flare hasn't quieted by then, should prompt a phosphate-sparing alternative agent instead of a repeat course of the same drug — left as a question for that visit rather than decided in advance of data that doesn't exist yet.