Anemia (Methemoglobinemia) in Dogs

This is a condition brought on by one of two things: a genetic disorder or from ingestion of analgesic tablets. These include all over the counter anti-inflammatory drugs. The genetic predisposition has two variations - one common and one not, but analgesic toxicity is a very real risk for any animal.

Methemoglobinemia is the result of the protein hemoglobin being able to carry oxygen to tissues, but being unable to release it effectively. This is a relatively straightforward problem, but it must be addressed quickly if severe, long term damage is to be minimized.

Symptoms will vary slightly depending on the cause of the methemoglobinemia. Look for the follwing as signs of poisoning.

• A bluish tinge to the skin. This indicates a lack of oxygen to the tissues.
• Low blood pressure
• Lethargy
• Seizures
• Hypothermia
• Hyperthermia
• Excessive panting
• Vomiting
• Abdominal pain
• Pale mucous membranes

Types 

There are two variations.

Genetic

• Type 1: This occurs when an enzyme called B5 reductase doesn't exist in the blood. This is very rare as this is a recessive disorder and must be passed down by both parents
• Type 2: This occurs when that same enzyme doesn't work within the body. This can be passed on by a single parent.
• B5 reductase is the enzyme which regulates the amount of oxygen your cells can carry.

External

• This is what you are most likely to see in your dog. This is caused by the overdose of any analgesic.

The most common cause is an overdose of an external analgesic. The ones veterinarians see the most often are: 

• Aspirin
• Ibuprofen
• Acetaminophen
• Naxproxen

It should be noted that of all of these, acetaminophen often has the most severe symptoms and damage to canine bodies due to its rapid absorption. 

Diagnosis of this condition is relatively straightforward. If your dog is displaying signs of anemia, see your veterinarian immediately. Be prepared with their medical history including vaccinations, symptoms and symptom duration. If you witnessed them ingest the medication, or suspect your dog of having ingested the non-steroidal-anti-inflammatory drugs (NSAIDS), include that in the information relayed to your veterinarian. To test for methemoglobinemia, your veterinarian will do an enzyme assay to determine the reductase levels in your dog. A Coombs test will likely be ordered. This examines the presence of antibodies in the blood. The presence of antibodies often directly corresponds to whatever they are fighting off. A telltale sign of this condition is a chocolate brown color present in the blood even when the blood is oxygenated. The veterinary team may need to do this test later in the diagnostic process regardless of whether your dog has consumed NSAIDS to determine the extent of the damage done to their circulatory system. A complete blood count and urinalysis will likely be ordered to rule out any other causes of disease.

The first goal of treatment for the ingestion of NSAIDS is to minimize damage to your dog's system. This may mean giving your dog an emetic (vomit inducing compound) to minimize absorption and therefore damage to their organs. If their symptoms are very severe, or the drugs were ingested too long ago, purging may be forgone in favor of oxygen therapy, and intravenous fluids including methylene blue, acetylcysteine and sodium chloride. Arterial blood gas samples will be needed to determine oxygen levels and your dog will need to be monitored closely. Blood transfusions may be necessary as well. No surgical treatment should be necessary for this condition and the treatment itself is relatively low-risk while the toxin itself is extremely high risk. The greatest problem with the treatment of this toxin is that your pet can appear healthy and okay enough to be released from veterinary care, but they can still manifest damage to organs days or even a week to two weeks later. Therefore, liver and kidney function should be checked 24, 48 and sometimes 72 hours after treatment.

Management: As mentioned, follow-up appointments are extremely important for this condition. It should be considered that a permanent problem with the red blood cells after an episode is not an unrealistic possibility. Prognosis will depend on the severity of the symptoms when they were treated and which type of condition it is. If it is a genetic problem, your veterinarian will discuss management strategies with you. If it was a one-time ingestion of NSAIDS, you will need to make sure the same medications are not available to your dog again. If there was long-term damage to their system, it is important to follow the instructions given by your veterinarian closely.