Hemolytic Anemia in a Horse: When the Blood Smear Cracked the Case

Ready for a case challenge?

This is a horse case, but even if you’re a small animal practitioner, you’ve probably learned of this at some point even if you haven’t treated a horse since school.

This is a blood smear from an 18 month old F Quarterhorse. The owner noticed she had red urine so called her vet out. The vet submitted blood for a CBC, and found she was anemic at 20% as well as isosthenuric.

Let’s take a look at the blood smear:

Two questions to think about before scrolling down:

1) What abnormality is most prominent on this blood smear? (Clue- look at the RBCs). There is a little stain debris artifact (small blue dots), so just ignore that.

2) If this was your case, what is the first thing you would ask the owner after seeing this blood smear?

Ok, so now that you’ve thought this through, let’s talk about the answer with picture annotations!


Answer: Frequent eccentrocytes (blue circles) with fewer Heinz bodies (green arrow) supports oxidative damage. This can be seen in a number of pathologies, but in this horse’s case, in light of the signalment and history, I want to know if there are red maples on the property.🍁 

The vet asked the owner this, and she said no. Hm. Well, that’s perplexing.

However, a few days later she called the vet back and said she had scoured the pasture and found a large pile of dried red maple leaves that had blown in from a surrounding property. With this, we can safely assume that this is a case of red maple toxicosis.

Red maple toxicosis leads to oxidative damage of the red blood cells which leads to hemolytic anemia. These horses also can have methemoglobinemia (their blood will look chocolate brown) as well as renal failure. As far as I understand it, the prognosis is guarded.