Last Monday, I (Perry Jameson) arrived to find a middle-age miniature Schnauzer transferring to me from our ER department for severe anemia. He was extremely depressed and so anemic that a transfusion had to be administered.
Later the same day, I walked into my last appointment of the day to find my patient was a 15-year-old Labrador. He jumped up to greet me and tried to even lick me on the face. I was surprised how good he looked based on the fact that he was coming to me for anemia, as I thought he would be weak and depressed.
Both of these dogs were here to see me so that I could figure out why they were anemic, and what could be done for them.
Anemia is marked by a decreased number of red blood cells. To figure out why there are not enough, I divide the problem into the following two categories: regenerative and nonregenerative anemias. This helps me to not only narrow down the number of possible causes, but also the tests needed to figure out the cause.
These different categories of anemia are defined by how the bone marrow is responding. The bone marrow is where the majority of the cells in the blood are produced, the red blood cells as well as the white blood cells and platelets.
For all animals, red blood cells have a defined life span. In dogs, it is about 100 days. So some cells are 1 day old while others are 100 days old, with most being somewhere in between. When they reach 100 days, the body removes them from circulation, saves the iron to make new cells and eliminates the rest. As each of these cells age out, the bone marrow makes a new cell so the levels remain constant.
Nonregenerative anemias occur when there is a disease preventing the bone marrow from replacing red cells as they naturally die off. This causes a gradual drop in red blood cell levels. Now since most of our pets live sedentary lives, this slow drop does not produce any visible outward symptoms at first. However, eventually, levels get low enough and Mom and Dad find their pets sleeping more, tiring with activity and, in the later stages, weakness and labored breathing.
The bone marrow may not replace red blood cells at a normal rate for multiple reasons. There are several insect-transmitted infections that can produce this. Cancer in the bone marrow will crowd out and replace the normal cells causing a nonregenerative anemia. Any chronic longstanding disease elsewhere in the body may do this, often cancer or infection. The kidneys produce a hormone that stimulates red cell production so dogs with severe renal disease may become anemic.
Regenerative anemia, of course, then is the exact opposite. Here the bone marrow is replacing red blood cells as it should. When there is a sudden loss of a large number of red cells, the marrow will attempt to replace them as quickly as possible by pumping out young immature red blood cells called reticulocytes.
Regenerative anemias are the result of bleeding or hemolysis. Bleeding is obvious if you see it. Sometimes it is hidden when the bleed is internal or into the GI tract.
Hemolysis is where red blood cells are being destroyed within the body. The most common cause for hemolytic anemia is immune mediated. This is where, for an unknown reason, the dog’s own immune system attacks and destroys the cells. Hemolysis may also occur with certain cancers, severe heartworm infections, toxins and some infections.
Both of my patients had regenerative anemias. Their bone marrows were healthy, trying to kick out enough red blood cells but just could not keep up.
Further testing revealed the Schnauzer to have immune-mediated hemolytic anemia. This is a serious condition that is difficult to treat with reports of anywhere from 30-60 percent of dogs dying despite heroic efforts. He is still being treated and, hopefully, will respond.
The old Lab had changes on blood work consistent with blood loss and iron deficiency. The fact he looked so good indicated to me things had changed slowly so he was adapting for a while. In questioning Mom, he had recently been started on a NSAID for arthritis. Now, these newer aspirin type drugs are much safer than in the past, but we still have occasional GI bleeding. He has done well since stopping the medication and starting antacids and GI protectants.