The sedimentation rate test measures inflammation in the body. It is also called the sed rate or the erythrocyte sedimentation rate (ESR) test. It is a blood test. It determines how quickly red blood cells sink in a tube of blood.
The sedimentation rate test is used to diagnose, or to assess the progress of, inflammatory diseases, such arthritis and polymyalgia rheumatica, and autoimmune disorders, such as lupus. It is sometimes used to help diagnose cancer and tuberculosis. The test can also show the effect of treatments for conditions that cause inflammation. It is usually done at the same time as other tests.
The test can identify and measure inflammation in your body. It does not help identify the cause of inflammation.
In people with inflammation, red blood cells cling together, forming clumps. This clumping affects the rate at which red blood cells sink in a tube of blood. The sedimentation rate test allows your doctor to see how much clumping is occurring. The faster the red cells sink to the bottom of a test tube, the more likely it is that inflammation is present.
The sedimentation rate test doesn’t require preparation. You simply show up for your appointment and have some blood drawn. You might feel the prick of the needle and mild pain or throbbing after the blood test is complete.
The sample will go into a thin tube and sit for one hour. During and after that hour, your doctor will assess how far down the tube the red blood cells have sunk, how quickly they sank, and how many sank.
Clumped red blood cells sink lower and faster than individual cells. You doctor will look at how far the red blood cells sank (in millimeters) in the hour of the test. This will give an idea of how much inflammation is present and what next steps should be taken. For men, 0–22 millimeters in an hour is normal. For women, 0–29 millimeters in an hour is normal. Higher numbers mean more inflammation.
If you are pregnant or have anemia, kidney issues, or high cholesterol, the test results could be inaccurate.
If high inflammation is confirmed, your doctor will probably want to do additional testing to find the cause of the inflammation.
The only risks of sedimentation rate testing are those associated with any blood draw. These include very light bleeding, bruising, or tenderness at the site of the draw.