Methemoglobinemia in Cats
The purpose of hemoglobin in the blood is to carry oxygen from the lungs to other parts of the body. Methemoglobin is the result of iron oxygenation, and while it is a form of hemoglobin, it does not carry oxygen.
Under normal conditions, methemoglobin is converted back to hemoglobin, and a balance is maintained. But when there is too much methemoglobin in the blood, inadequate oxygenation of the cat’s bodily tissues results. A visible sign of methemoglobinemia is when the blood becomes brownish in color, instead of the normal oxygenated rich red color. Methemoglobinemia can be the result of a genetic disorder, or it can be caused by later exposure to certain chemical agents.
Symptoms of Methemoglobinemia
- Depression
- Weakness
- Rapid breathing
- Rapid heart rate
- Discoloration of skin and mucous membranes
- Swelling of the face
- Excessive drooling
- Jaundice
- Vomiting
- Hypothermia
- Incoordination
- Coma
- Death
Causes of Methemoglobinemia
- Genetic disorder
- Acetaminophen ingestion
- Ibuprofen ingestion
- Topical anesthetics such as benzocaine
- Skunk (foul) musk odor
Diagnosis of Methemoglobinemia
Your veterinarian will want to know whether your cat has ingested acetaminophen or ibuprofen, or whether you have applied a topical medication. Blood tests may also be done at a laboratory to examine the levels of methemoglobins. If the methemoglobinemia is chronic, it is likely that the blood test will reveal a high volume of red blood cells.
On the other hand, if the anemia is severe, or the cause is exposure to drugs such as acetaminophen, ibuprofen, or a topical medication, the veterinarian will look for evidence of organ injury.
A spot test may be performed, by which a drop of the cat’s blood will be placed on an absorbent white paper and a drop of normal blood will be placed next to it. If the cat is suffering from methemoglobinemia, its blood will be noticeably browner than the bright red of the normal blood spot.
Treatment for Methemoglobinemia
- Mild to moderate — no treatment necessary
- If drug-induced, discontinuation of the drug
- Acetaminophen or ibuprofen overdose — vomiting induced immediately
- Inherited — some animals have normal life expectancy and do not require treatment
- Severely anemic — blood transfusions
- Electrolyte imbalances resulting from vomiting, diarrhea, kidney injury, or impending shock may be treated with IVs
- In cases of severe anemia, methylene blue may be administered intravenously to reduce the methemoglobin count
Living and Management of Methemoglobinemia
Do not administer over-the-counter medications to your cat without your veterinarian’s advice and/or approval, particularly medications such as acetaminophen and ibuprofen. If your cat has ingested one of these medications by accident, induce vomiting if possible and take the cat to the veterinarian or emergency clinic immediately.
Color should return to the skin and mucous membranes once the amount of methemoglobin in the blood has returned to a level that is not critical and blood on the spot test appears bright red. If methylene blue treatment has been given, the proportion of red cells in the blood should be monitored closely.