Why Might My Dog 's Red Cell Distribution Width Be Increased ?
Why Might My Cat 's Red Cell Distribution Width Be Increased ?
To see what normal blood and urine values are for your pet, go here
For an explanation of causes of most abnormal blood and urine tests go here
To see how tests are often grouped, go here
Ron Hines DVM PhD
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Red Cell Distribution Width
RDW , RCDW
Your pet’s red blood cells (erythrocytes) should be very uniform in size. They make up ~25% of all the cells in your pet’s body. It is thought that the average dog produces and destroys about 800,000 RBCs every second.
Red blood cell size must be extremely small and uniform to pass through the small capillaries of your pet’s body without hindrance (getting stuck). One factor in determining their size is the number of cell divisions that occur between their formation from stem cells in your dog or cat 's bone marrow and the time they leave the marrow. (a protein [cyclin D3] is involved in that regulation).
In certain health issues, red blood cells may not be as uniform in size as they should be. Veterinarians use a mathematically calculated value, the RDW, to know when that is happening. The actual measurement is of the volume or size of your pet’s RBC (its MCV). A high RDW means that there is too much variation in the size of your pet’s RBCs.
Why Your Pet’s RDW Could Be High :
The RDW is not a stand-alone test. I do not put much faith in its ability to differentiate one cause of anemia from another. But it does add a bit to the evidence - if the rest of your pet’s blood work agrees with what is generally accepted as the causes of abnormal RDW:MCV relationships.
When your pet has a vitamin B12 deficiency, as might occur with chronic intestinal problems like IBD , Its RDW will increase. The same thing can occur with a folic acid (folate) deficiency. In both cases the MCV tends to be elevated as well. In those cases, anisocytosis is usually also noted on the pet’s CBC/WBC results.
High RDW can also occur in iron deficiency anemia. In those cases, the MCV is often low.
Recent hemorrhage or blood loss will elevate RDW but MCV usually remains normal.
Fragmentation (turbulence) anemia or any anemia in which the RBCs are destroyed while in the pet's circulation (hemolytic anemia) can cause RDW to be high and MCV to be low.
In humans, high RDW is sometimes associated with liver disease. We do not know if that known in the case in dogs and cats.
A combination of the above causes can also be responsible for an elevated RDW in your dog or cat.