The erythrocyte sedimentation rate (ESR) is also called the ‘sed rate’ and it tests the rate at which red blood cells sediment (or settle) in a period of one hour.  It is a common test and is a non-specific measure of inflammation.  The ESR is governed by the balance between pro-sedimentation factors (mainly fibrinogen) and those factors resisting sedimentation (namely the negative charge of the erythrocytes).  When an inflammatory process is present, the high proportion of fibrinogen in the blood causes red blood cells to stick to each other, called a ‘rouleaux’, which settles faster. Rouleaux formation can also occur in association with some lymphoproliferative disorders in which one or more immunoglobulin are secreted in high amounts.  Your health care practitioner will generally order an ESR test if an inflammatory condition is suspected, or if monitoring of an inflammatory condition is required.


The C-reactive protein (CRP) is often used to detect or monitor significant inflammation in an individual who is suspected of having an acute inflammatory condition from (a bacterial infection such as sepsis, or a fungal infection, pelvic inflammatory disease, arthritis and/or autoimmune diseases, etc).  The test is also performed routinely after surgery in order to identify any post-surgery infection.


A CRP (or a high sensitivity CRP) test may sometimes be ordered along with an ESR, and depending upon the suspected illness a number of other tests may also be performed to identify the source of the inflammation.  Both the CRP and ESR tests give similar information about the presence of inflammation, however CRP appears and disappears sooner than changes in the ESR.  For instance your CRP will fall to normal if your arthritis flare-up has been treated successfully, but your ESR may still be elevated for longer.


Sometimes a high-sensitivity C-reactive protein test is performed to assess your risk of heart disease.