A man in his 40s received iron injections to treat anemia and developed a serious drop in phosphate levels in his blood—a mineral your body needs to stay healthy. Even though he was otherwise healthy with normal kidney function, his phosphate levels fell so low that he needed extra treatment and couldn’t leave the hospital for eight extra days. This case shows that iron injections, while helpful for anemia, can sometimes cause this dangerous side effect that doctors don’t always expect or watch for carefully enough.

The Quick Take

  • What they studied: Whether iron injections used to treat anemia can cause dangerous drops in phosphate levels in the blood
  • Who participated: One man in his 40s who received two large doses of iron injection (ferric carboxymaltose) one week apart for iron deficiency anemia
  • Key finding: The patient’s phosphate levels dropped to a dangerously low level (0.20 mmol/L, far below normal) even though his kidneys worked normally and he was otherwise healthy. This required multiple treatments with phosphate and kept him in the hospital 8 extra days
  • What it means for you: If you receive iron injections for anemia, doctors should monitor your phosphate levels afterward, especially if you receive multiple doses. This is a rare but serious side effect that can happen even in younger, otherwise healthy people

The Research Details

This is a case report, which means doctors documented what happened to one specific patient in detail. The patient came to the hospital with iron deficiency anemia (not enough iron in the blood) and received two doses of ferric carboxymaltose, a type of iron injection, within one week. Doctors then tracked what happened to his blood minerals, kidney function, and other health markers over time.

Case reports are like detailed medical stories that help doctors recognize patterns and potential problems they might not have seen before. While they only describe one person’s experience rather than testing many people, they can be very important for spotting unexpected side effects of treatments.

This research approach is important because it shows a real-world example of a side effect that might not show up in typical studies. Doctors need to know about unusual but serious complications so they can watch for them and treat them quickly. This case suggests that routine blood tests checking phosphate levels should happen after iron injections, especially when patients receive multiple doses.

As a case report of one patient, this study has limitations but provides valuable real-world evidence. The doctors carefully documented the patient’s blood tests and medical history, which makes the information reliable. However, because it’s only one person, we can’t say how often this happens to others. The patient had normal kidney function and only mild vitamin D issues, which makes this case more surprising and important to report, since doctors might not expect this problem in someone so otherwise healthy.

What the Results Show

The patient received his first iron injection (1,000 mg) and then a second identical dose just one week later. After these injections, his phosphate levels dropped dramatically to 0.20 mmol/L—this is extremely low and dangerous (normal is around 0.8-1.4 mmol/L). Despite having normal kidney function and normal calcium levels, his body couldn’t maintain adequate phosphate.

The low phosphate caused problems serious enough that he needed intravenous phosphate replacement (medicine given directly into his veins). Even with this treatment, his phosphate levels stayed dangerously low for an extended period. The hospital couldn’t discharge him until his phosphate levels improved and stabilized, which took eight additional days beyond when he would normally have been ready to go home.

What made this case particularly notable is that the patient was relatively young (in his 40s) and otherwise medically healthy. Doctors might expect this kind of severe complication in older patients or those with other health problems, but this case shows it can happen to anyone receiving these iron injections.

The patient’s kidney function remained normal throughout the episode, which is important because kidney problems usually cause phosphate imbalances. His calcium levels were also normal. He had only borderline vitamin D insufficiency, which is very common and wouldn’t typically cause such severe phosphate problems. This means the iron injection itself, rather than other underlying health issues, was the likely cause of the dangerous phosphate drop.

While ferric carboxymaltose is known to sometimes cause low phosphate levels, this complication is often overlooked or underestimated by doctors. Previous research has noted that low phosphate can occur after these iron injections, but it’s frequently dismissed as temporary and harmless. This case demonstrates that in some patients, the drop can be severe, prolonged, and serious enough to require hospitalization and delay discharge. It suggests that the risk may be higher than commonly recognized, particularly when patients receive multiple doses within a short time period.

This is a single case report, so we cannot determine how often this complication occurs or who is most at risk. We don’t know if this patient had any genetic factors or other hidden conditions that made him more susceptible. The report doesn’t include information about whether the patient had any symptoms from the low phosphate or what those symptoms were. We also can’t compare this to what would have happened if he’d received the iron injections differently (like smaller doses spread further apart). Finally, because this is one unusual case, we can’t make broad recommendations for all patients—more research with larger groups of people would be needed to do that.

The Bottom Line

If you receive iron injections (ferric carboxymaltose), ask your doctor to check your phosphate levels in the days and weeks after treatment, especially if you receive multiple doses. This is a precautionary measure based on this case and emerging evidence. If you experience muscle weakness, bone pain, or unusual fatigue after iron injections, report it to your doctor immediately. (Confidence level: Moderate—based on one case, but supported by growing awareness of this complication)

This matters most for people receiving iron injections for anemia, particularly those getting multiple doses. It’s especially important for people with kidney disease, those taking certain medications, or anyone who develops symptoms after iron treatment. Doctors and hospital staff should be aware when administering these injections. People with normal kidney function shouldn’t assume they’re protected from this complication.

The dangerous phosphate drop can happen within days of receiving the iron injection. In this case, it was severe enough to require hospitalization and took over a week to resolve even with treatment. Some patients may recover faster, but this case shows that recovery can be prolonged. Monitoring should continue for at least 1-2 weeks after iron injection treatment.

Want to Apply This Research?

  • If you receive iron injections, track your phosphate levels weekly for 4 weeks after treatment. Record the actual blood test values and note any symptoms like muscle weakness, fatigue, or bone pain. This creates a clear picture of your individual response.
  • Set reminders to get blood tests done 3-7 days after iron injection, then again at 2 weeks and 4 weeks. Keep a symptom log noting energy levels, muscle strength, and any unusual aches. Share this data with your doctor at follow-up appointments.
  • Create a long-term tracking system if you receive iron injections regularly. Document each injection date, dose, and subsequent phosphate levels. Over time, this helps identify patterns in your personal response and alerts you and your doctor to any concerning trends that might need intervention.

This case report describes one patient’s experience with iron injection treatment and is not medical advice. Iron injections are an important and generally safe treatment for anemia when used appropriately. However, this case highlights that serious complications can occur. If you are receiving or considering iron injections, discuss the benefits and risks with your doctor, including the potential for phosphate level changes. Do not stop or change any prescribed treatment without consulting your healthcare provider. Anyone experiencing symptoms like severe weakness, bone pain, or unusual fatigue after iron treatment should seek immediate medical attention. This information is educational and should not replace professional medical evaluation and care.