Methemoglobinemia in Animals

Methemoglobinemia is a blood disorder characterized by "an abnormal amount of hemoglobin" building up in the blood. Hemoglobin is found in the red blood cells that carry oxygen around the body. In both humans and animals the condition is either inherited or acquired by ingesting excessive nitrates in food and water and some pharmaceuticals.

  1. Definition

    • Methemoglobin forms in the blood when hemoglobin is oxidized, changing the form of the iron in the blood. This does not present a problem for a healthy animal as the methemoglobin is converted back to hemoglobin. However, if this process is inhibited, the methemoglobin builds up and the blood levels of oxygen decrease. As a result the organs do not receive sufficient oxygen to function, and if left untreated, the condition is potentially fatal.

    Causes

    • If not an inherited disorder, methemoglobinemia in animals is frequently caused by accidentally ingesting painkillers containing acetaminophen or ibuprofen. Cats are more sensitive to these medications than dogs, and one 250 mg tablet could cause liver failure. The disorder is also caused by topical anesthetics such as benzocaine, or by being sprayed with skunk musk. Livestock often contract the condition because of excessive amounts of nitrates in ground water.

    Symptoms

    • The symptoms vary, however, there are signs to watch out for including vomiting, difficulty breathing, facial swelling, uncoordinated movements and discoloured gums. In some cases, particularly if painkiller poisoning causes the methemoglobinemia, jaundice, a symptom of liver failure with obvious indicators such as yellow tinge in the eyes, is likely to occur.

    Diagnosis

    • To ensure proper diagnosis, a vet will initially carry out blood tests to establish the levels of methemoglobin in the blood. As it may take time to receive blood test results, the vet may carry out a spot test. This entails a drop of the animal’s blood being placed on absorbent white paper alongside a drop of healthy blood. Healthy blood is distinctly red, whereas blood with a high level of methemoglobin is brown-tinged because of the lack of oxygen.

    Treatment

    • Animals with mild symptoms and those that have inherited the condition do not require treatment. If an animal has ingested painkillers, the vet will induce vomiting immediately. If the condition is severe, treatment includes blood transfusions, an intravenous drip to restore electrolyte balance, and in the most severe cases the vet may administer a treatment called methylene blue to remove excess methemoglobin.