• Physicians take blood for an ESR when a patient's other symptoms suggest inflammation.drawing blood image by Pix by Marti from Fotolia.com
  
  An erythocyte sediment rate test (ESR) tests how quickly red blood cells fall to the bottom of a test tube. If the red blood cells fall significantly more quickly than expected, it may indicate abnormal protein in the blood associated with inflammation, according to kidshealth.org. ESR tests help support diagnoses but cannot be used on their own to diagnose patients, as an elevated ESR can have several causes and does not pinpoint the source of inflammation in the body.
  
  

Initial Ordering

• A physician often orders an erythrocyte sedimentation rate, or ESR, test when he suspects a disease is causing inflammation. For example, if a patient has symptoms of arthritis such as joint stiffness and pain, the doctor might order an ESR to support his diagnosis. ESR tests cannot pinpoint the exact location of inflammation; they only show that there is inflammation somewhere in the body, according to Lab Tests Online.
  
  

Frequency of Tests

• The physician might take ESR tests at regular intervals to determine the effect a disease is having on the body. A single ESR test showing elevated sedimentation rates does not necessarily indicate disease, as the test does not give the physician specific information about where the inflammation is located or what is causing it.
  
  

Interpretation of Test Results

• An ESR test by itself is rarely enough to make a diagnosis. Physicians usually compare ESR results with the results of other clinical tests, the patient's health history and the patient's current symptoms to make or rule out a particular diagnosis. If the ESR is unusually high, the doctor might order other tests to determine the cause, such as blood cultures, a serum protein electrophoresis test or a clotting protein test.
  
  

ESR Procedures

• The physician or lab assistant must take blood from the patient to do an ESR test. She does this by sterilizing the patient's forearm, wrapping an elastic tourniquet around the patient's arm, and collecting blood from the vein in a syringe. After collecting blood, the lab assistant puts cotton on the wound and bandages it. The physician then analyzes the collected blood. The physician can usually complete an ESR test within a few hours, according to kidshealth.org.