Times change and my website needed to change too. To see the 2020 update of this page click this link
To see what normal blood and urine values are, go here.
For an explanation of causes of most abnormal blood and urine tests, go here
To see how tests are grouped, go here
Read 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 fibrinogen) 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 there is a problem – but not what it is. More modern tests that detect inflammation like C-reactive protein (tests that monitor acute-phase response) have largely replaced the ESR.
The ESR test might also have value in deciding if your pet is responding as well as hoped for to its treatment.
A common cause for an elevated ESR rate in dogs and cats is anemia.
The ESR rate also goes up significantly in sudden (acute) generalized infections – the kinds that affect the whole body, cause widespread inflammation, produce fever and make your dog or cat visibly ill.
Pets with severe long-standing arthritis, or cancer that is causing visible decline in their health can also increase their ESR rate.
Sed rates were once reported to be elevated in dogs with roundworm infection – but other health factors could have been the underlying cause.
Blood samples that have been stored tend to give falsely lower ESR rates - particularly if that storage was at room temperature and not in the refrigerator.
It is said that hemolytic anemia – the kind of anemia due to toxins or antibodies that destroys a pet’s red blood cells while they are still in circulation – can decrease ESR rates. It has also been discussed that low blood fibrinogen levels due to liver disease might slow your pet's ESR rate. In humans, anemia from a variety of causes, 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 also slows ESR.
It would be quite unusual for a cat or a dog's ESR to be abnormal in the absence of other abnormalities in the pet's CBC. ESR is just a marker of inflammation. As such, it does not tell your veterinarian where or why that inflammation is occurring. It only tells your veterinarian that there is a health issue. Hopefully, other abnormalities in your pet's CBC, physical examination and the history you provide will give your vet hints as to how to proceed in making the diagnosis.