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Methemoglobinemia in Dogs

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 bodily tissues ensues. A visible sign of methemoglobinemia is when the blood becomes brownish in color, instead of the normal oxygen 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

• Depression
• Weakness
• Rapid breathing
• Discoloration of skin and mucous membranes
• Jaundice
• Vomiting
• Hypothermia
• Swelling of face or jaw

Causes

• Genetic disorder
• Acetaminophen ingestion
• Ibuprofen ingestion
• Topical anesthetics such as benzocaine
• Skunk musk

Diagnosis

Your veterinarian will want to know whether your dog 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 — where a drop of the dog’s blood will be placed on an absorbent white paper and a drop of normal blood will be placed next to it. If the animal is suffering from methemoglobinemia, its blood will be noticeably browner than the bright red of the normal blood spot.