Sedimentation Rate (Sed Rate) - What Does It Tell About Arthritis?

Typically the First Test Your Arthritis Doctor Will Order

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A sedimentation rate, also commonly referred to as a sed rate, is a blood test that detects nonspecific inflammation in the body. Nonspecific means the test does not identify the source of the problem or illness that is causing the inflammation. An elevated (abnormally high) sedimentation rate does suggest that there is an ongoing inflammatory process.

If you consult a doctor because you are experiencing persistent joint pain, the doctor will perform a ​physical examination and order diagnostic tests.

You should expect your doctor to order x-rays of the affected joints, as well as certain blood tests. A sedimentation rate is typically among the first blood tests ordered when arthritis is suspected. A sedimentation rate can also be elevated when there is an infection or tumor present. Illnesses associated with the breakdown or decreased function of tissue or organs can also cause an elevated sedimentation rate. Pregnancy is yet another condition linked to an elevated sed rate. Aside from diagnostic purposes, a sedimentation rate is often ordered periodically to check disease progress. Theoretically, as your condition improves, your sedimentation rate should decrease and approach the normal range.

How Is a Sedimentation Rate Performed?

When a sedimentation rate is performed, the blood sample is placed in a tall, thin, vertical tube. The test measures how fast the erythrocytes (red cells) settle in one hour.

The result is reported as millimeters per hour (that is, millimeters of plasma on top of the sediment of red cells).

Under normal conditions, when there is no inflammatory process or illness, red cells fall slowly. Increased levels of abnormal proteins in the blood or other proteins called acute phase reactants, such as fibrinogen or immunoglobulins which are increased in inflammation, cause red cells to drop more quickly.

Normal Reference Ranges for Sedimentation Rate

The usual method used for sedimentation rate is known as the Westergren method. As mentioned above, results are reported in mm/hr (millimeters per hour). Typically, the sedimentation rate increases with age and is higher in women. Many laboratories do not adjust for gender or age and consider that a normal sedimentation rate is:

  • Men: 0-15 mm/hr
  • Women: 0-20 mm/hr

When adjusted for age and gender, the accepted reference range for the test is:

Adults (Westergren method):

  • Men under 50 years old: less than 15 mm/hr
  • Men over 50 years old: less than 20 mm/hr
  • Women under 50 years old: less than 20 mm/hr
  • Women over 50 years old: less than 30 mm/hr

Children (Westergren method):

  • Newborn: 0 to 2 mm/hr
  • Newborn to puberty: 3 to 13 mm/hr

The Bottom Line

While no single test can diagnose arthritis, the sedimentation rate is useful for detecting types of arthritis associated with inflammation, such as rheumatoid arthritis, lupus and psoriatic arthritis. On the other hand, osteoarthritis is typically associated with a normal or modestly elevated result for sedimentation rate.

The sedimentation rate is often ordered in conjunction with another blood test, known as CRP or C-reactive protein. The CRP test also detects non-specific inflammation.


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