Why Complete Blood Picture & ESR test is done A complete blood count is a common blood test that's done for a variety of reasons: To review your overall health. Your doctor may recommend a complete blood count as part of a routine medical examination to monitor your general health and to screen for a variety of disorders, such as anemia or leukemia. Why Are ESR Tests Done Doctors may order an ESR test if a child has signs of inflammation or infection. They use ESR tests to follow conditions such as inflammatory bowel disease (IBD), arthritis, and lupus. ESR tests also can help doctors see how well treatment for inflammation or infection is working.