Category Archives: Laboratory tests

How is inflammation measured in arthritis?

The body responds to inflammation by changing the production of protein in the liver and other protein producing organs in the body. Proteins whose blood levels are altered by inflammation are called acute phase reactants.

The two most common methods for measuring acute phase reactants are the erythrocyte sedimentation rate (ESR) and the C-reactive protein (CRP).

sed-rateThe ESR, or as it is sometimes called, the “sed rate”, measures the speed at which red blood cells settle or “sediment” in a narrow tube over a one hour period of time. The speed that the cells settle is directly proportional to the amount of acute phase reactant proteins that are present in the blood. Because inflammation increases the amount of proteins in the blood, the sed rate increases. This is because when proteins coat red blood cells, they sediment faster leading to an increased rate of red blood cell sedimentation.

Unfortunately, the sed rate is not specific and can be altered by other circumstances such as anemia or inappropriate specimen handling.

CRP changes occur more rapidly and return to normal more quickly than changes in ESR. CRP is also not affected by anemia nor is it quite as susceptible to specimen handling errors.crp-machine

Measurement of acute phase reactants is important in arthritis disorders since elevations indicate the presence of inflammation while normal values indicate that inflammation is not present. Serial measurement of acute phase reactants is important for monitoring therapy in diseases such as rheumatoid arthritis, polymyalgia rheumatica, and giant cell arteritis.

The upper levels for both ESR and CRP are influenced by both gender and age.

Your rheumatologist will best be able to interpret these values.

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