30/09/2026
Ferritin finally up after your iron infusion… so why do you feel worse? 💉
Comment IRON below 👇🏼
On 1 September 2026, the US FDA added a Boxed Warning, its highest safety alert, to ferric carboxymaltose (Ferinject) for symptomatic hypophosphataemia (dangerously low phosphate).
In short: this infusion can raise a hormone called FGF23, which tells your kidneys to dump phosphate.
Here’s the kicker. Low phosphate looks like low iron: fatigue, weakness, breathlessness, headaches. If you still feel flat after your infusion, the infusion may not have “failed.” Your phosphate may have crashed. In severe or prolonged cases, low phosphate can cause bone pain, muscle weakness, osteomalacia (soft bones) and fractures.
Everyone assumes I’m anti-infusion. I’m not. But true iron deficiency anaemia must be confirmed first. The right product chosen. The right dose determined. And every potential side effect discussed.
IV iron is brilliant when oral iron hasn’t worked or can’t be tolerated. But before you book one:
✔️ Ask which formulation you’re getting. Ferinject isn’t the only option, and ferric derisomaltose (Monofer) causes low phosphate far less often.
✔️ Ask for phosphate testing, especially if you’ve had a repeat infusion within 3 months.
✔️ Get FBE/CBC, CRP and full iron studies, never ferritin alone.
✔️ And as always, figure out WHY you’re low in the first place.
Test, don’t guess 🔍
Comment IRON below and learn how to read your full iron studies like a pro.
