Ron Hines DVM PhD
See What Normal Blood & Urine Values Are
Causes Of Most Abnormal Blood & Urine Tests
Your Pet’s Blood Sedimentation Rate = Erythrocyte Sedimentation Rate, Sed Rate, ESR, Westergren ESR
Read a second Vetspace article on ESR with a slightly different explanation here.
This vintage test (since 1897) does little more than confirm to your veterinarian that your dog or cat really has a health issue. It measures how fast your pet’s red blood cells (RBCs) sink to the bottom of a glass tube in which a blood sample with added anticoagulants was placed.
That rate, measured over a period of one hour, increases when inflammation is present anywhere in the body. The test relies on changes in the electrical charges between RBCs that keep them in suspension versus clotting factors that cause RBCs to stick to one another (rouleaux formation, high blood fibrinogen level) and sink to the bottom. Because anemia markedly increases your pet’s sedimentation rate, laboratories have a mathematical formula to correct the ESR number (value) when anemia is present.
Tests like the ESR are called “high sensitivity-low specificity” tests. Like having a fever, they tell you that there is a problem – but not what it is. More modern tests that detect inflammation, such as the C-reactive protein test that monitors acute-phase response, have largely replaced the ESR test.
The ESR test might also have value to your veterinarian in deciding if your cat or dog is responding as well as hoped for to its treatment.
Reasons Why Your Dog And Cat’s Sed Rate Might Be Increased:
A common cause for an elevated ESR rate in dogs and cats is anemia. With less red blood cells (erythrocytes) in your pet’s body, its blood is dilute and the RBCs that are still present fall to the bottom of the ESR glass tube faster. Red blood cells that are abnormally large (macrocytosis) also settle to the bottom of the tube faster than normal, raising the sed rate.
The ESR rate also goes up significantly in sudden (acute) generalized infections – the kinds that affect the whole body and which cause widespread inflammation. These infections usually produce fever and make your dog or cat visibly ill. The cause could be bacterial or a viral.
Dogs and cats with severe, long-standing arthritis, or pets suffering from cancers that releases inflammatory compounds often have elevated sed rates. Those pets usually show other visible signs of their declining health.
Sed rates were once reported to be elevated in dogs with intestinal roundworm infections – but other health issues could have actually been the underlying cause.
Reasons Why Your Dog And Cat’s Sed Rate Might Be Decreased:
Blood samples that have been stored tend to give falsely lower ESR rates – particularly if that storage was at room temperature and not in a refrigerator. It has been published that hemolytic anemia – the kind of anemia due to toxins or autoantibodies that destroy a pet’s own red blood cells have the ability to decrease ESR rates. It has also been discussed that low blood fibrinogen levels due to liver disease might slow your dog and cat’s ESR rate as well. In humans, anemia from a variety of causes such as advanced age, kidney or thyroid issues and a variety of medications have also been linked to changes in ESR rate. Anything that increases the viscosity of blood, such as dehydration, might also slow your pet’s ESR rate.
Complementary Tests That Come To Mind:
It would be quite unusual for your cat or dog’s ESR to be abnormal in the absence of other abnormalities in your dog or cat’s CBC / WBC and blood chemistry tests. ESR is just a general marker of inflammation. As such, a high ESR does not tell your veterinarian where or why that inflammation is occurring. It only tells you and your veterinarian that there is a health issue somewhere. Hopefully, other abnormalities in your pet’s lab report, your veterinarian’s physical examination and the history you provide will give your veterinarian hints as to how to proceed in making a diagnosis.
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