Iron poisoning: symptoms, diagnosis, treatment

Iron poisoning is the leading cause of poisoning death in children. Symptoms begin with acute gastroenteritis, progressing to a latent period, then shock and liver failure. Diagnosis is by measurement of serum iron, detection of radiopaque iron tablets in the gastrointestinal tract, or unexplained metabolic acidosis in patients with other symptoms suggestive of iron poisoning. Ingestion of large amounts of iron requires complete bowel lavage and treatment with intravenous deferoxamine.

Many over-the-counter medications contain iron. The most common iron-containing medications and prescription medications are ferrous sulfate (20% pure iron), ferrous gluconate (12% pure iron), and ferrous fumarate (33% pure iron). Children may take iron tablets like candy. Prenatal multivitamins contain iron and have been a common cause of fatal poisoning in children. Children's chewable multivitamins are low in iron and rarely cause poisoning.

Iron is toxic to the gastrointestinal tract, central nervous system, and cardiovascular system. The specific mechanism is unclear, but excess free iron is incorporated into enzymatic processes and impairs oxidative phosphorylation, causing metabolic acidosis. Iron also catalyzes the formation of free radicals, acting as an oxidizing agent when plasma protein bonds are saturated, iron and water form iron hydroxide and free H ⁺ ions, which also aggravates metabolic acidosis. Coagulopathy may occur early due to disturbances in the coagulation cascade, or later due to liver damage. Pure iron levels of <20 mg/kg are nontoxic; 20-60 mg/kg causes moderate poisoning, and >60 mg/kg may cause severe poisoning and complications.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ]

Symptoms of Iron Poisoning

There are 5 stages in the development of the clinical picture, but the symptoms themselves and their development vary. The severity of the symptoms of the first stage usually reflects the severity of the poisoning as a whole; the following stages of symptom development occur only if the symptoms in the first stage were moderate or severe.

Stages of Iron Poisoning

Stage	Time elapsed since poisoning	Description
I	Less than 6 hours	Vomiting blood, profuse diarrhea, irritability, abdominal pain, drowsiness. In severe intoxication - tachypnea, tachycardia, arterial hypotension, coma and metabolic acidosis
II	6-48 h	Up to 24 hours apparent improvement (latent period)
III	12-48h	Shock, seizures, fever, coagulopathy and metabolic acidosis
IV	2-5 days	Liver failure, jaundice, coagulopathy and hypoglycemia
V	2-5 weeks	Obstruction of the outlet of the stomach or duodenum due to scarring

Iron poisoning may be suspected after taking multiple medications (since iron is in virtually all medications) and in young children with access to iron who have unexplained metabolic acidosis or severe hemorrhagic gastroenteritis. Children often share, so family and friends of young children who have ingested iron-containing substances should also be evaluated.

Abdominal radiography is usually performed to confirm foreign body ingestion and may show undissolved iron tablets or iron deposits. However, chewed and dissolved tablets, liquid iron preparations, and iron in multivitamins may not be detected by radiography. Serum iron, electrolytes, and pH are measured 3 to 4 hours after ingestion. Symptoms that may suggest iron poisoning include vomiting and abdominal pain, serum iron >350 μg/dL (63 μmol/L), iron deposits visible on radiography, or unexplained metabolic acidosis. Iron levels may suggest poisoning, but do not confirm its presence. Total serum iron-binding capacity (TIBC) is often an imprecise test and should not be used to diagnose serious poisoning. The most accurate method involves sequential measurement of serum iron, HCO3 _, and pH, then evaluating the results together and relating them to the patient's clinical status. For example, poisoning is suspected by elevated serum iron, metabolic acidosis, worsening symptoms, or, most commonly, some combination of these symptoms.

Prognosis and treatment of iron poisoning

If there are no symptoms in the first 6 hours after ingestion, the risk of serious poisoning is minimal. If shock and coma develop in the first 6 hours, the risk of death is approximately 10%.

If radiocontrast tablets are visible on an abdominal radiograph, a colonic lavage with polyethyleneglycol is given, 1-2 L/h for adults or 24-40 ml/kg per hour for children, until the iron deposits are no longer visible on a repeat radiograph. Gastric lavage is usually useless; induced vomiting empties the stomach more effectively. Activated charcoal does not adsorb iron and is used only if other toxins have been ingested.

All patients with symptoms more severe than moderate gastroenteritis should be hospitalized. In severe poisoning (metabolic acidosis, shock, severe gastroenteritis, or serum iron >500 mcg/dL), intravenous deferoxamine is given to chelate free ions in plasma. Deferoxamine is infused at rates up to 15 mg/kg per hour, titrating the dose to the blood pressure. Because both deferoxamine and iron poisoning can lower blood pressure, patients receiving intravenous deferoxamine also require intravenous hydration.