If symptoms are not severe, your cat may not require treatment to recover. However, in the most extreme cases, your cat may need a complete blood transfusion to avoid coma or death. There’s no way for you to tell how severe your cat’s condition is on your own, so it’s not wise to wait and see if your cat recovers on his own. It’s strongly recommended that you always take him to a vet if you suspect he has methemoglobinemia.

Methemoglobin is a form of hemoglobin, which is the protein found in red blood cells that transports oxygen to different parts of the body. When an abnormal amount of methemoglobin is present in the blood, this is known as methemoglobinemia. With this condition, the hemoglobin may not be able to release oxygen into the tissues. Some cases of methemoglobinemia are inherited, however, most are caused by exposure to a toxic chemical or drug, such as acetaminophen, moth balls, benzocaine, phenazopyridine, and naphthalene. 

All cat owners should be familiar with the symptoms of methemoglobinemia to ensure they are able to quickly spot signs of trouble and bring their cat in for emergency medical treatment. Some of the most common symptoms include:

Although some forms of methemoglobinemia are believed to be genetic, the most common cause of this life-threatening disorder is exposure to certain medications. If cats inhale or ingest acetaminophen (a common pain reliever), moth balls, benzocaine, (a topical cream), phenazopyridine (a pain reliever), or naphthalene, (found in toilet bowl cleaners), they may develop methemoglobinemia. 

You should take your cat to a veterinarian as soon as possible after spotting these dangerous symptoms, as methemoglobinemia is a life-threatening condition. Tell the vet what symptoms you have observed, when they began, and if your cat has been exposed to any chemicals or been given any medications recently.

The vet will begin by performing basic tests, including a complete blood count, urinalysis, and blood chemistry profile. The vet should be able to diagnose your cat’s condition based on the oxygen levels present in the blood sample, as well as the color of the sample. Cats with methemoglobinemia will have much darker blood than healthy cats. 

After making this diagnosis, the vet will need to determine the extent of your cat’s condition. This is usually done with a spot test, which involves placing a drop of the blood onto a white sheet of paper. If the blood is noticeably brown, the methemoglobin content is believed to be 10 percent or greater, which is abnormal. 

If your cat is not exhibiting severe symptoms or signs of distress, the vet may say no treatment is necessary and ask that you continue to monitor his symptoms. Of course, if methemoglobinemia is caused by exposure to a certain medication, you should immediately stop administering this drug to your cat. The cat’s body should be able to reduce the amount of methemoglobin present in the bloodstream within 24 hours after the medication leaves the cat’s system. 

However, if your cat’s condition is severe, the vet may need to begin treatment immediately instead of waiting for the cat to naturally reduce the methemoglobin level. These cats may be given methylene blue slowly through an IV over a period of several minutes. The cat’s condition will be reassessed after thirty minutes to determine if an additional dose of methylene blue is needed.

If you gave your cat acetaminophen, the vet may administer N-acetylcysteine to treat toxicity. In extreme cases, the vet may perform a complete blood transfusion if he believes your cat is too weak to undergo other forms of treatment.

The sooner you take your cat to a veterinarian, the better his chances are of making a full recovery. Your vet may want to see your cat again a few days after treatment to retest his blood and confirm his condition is improving. 

Once your cat is back home with you, make sure you do not expose him to any of the chemicals or medications that could cause methemoglobinemia. Do not administer any medications that have not been approved by your vet, and keep toilet lids closed so cats are not exposed to the toxic chemicals found in toilet bowl cleaners. If you use any of the medications that can cause methemoglobinemia, make sure you do not drop any pills on the floor and keep your medicine cabinet door closed at all times.

Cats that have inherited this disease usually live a long and healthy life with only minor complications.