Depending on what is being tested, a blood test may not be more accurate than a urine test. Blood tests are more accurate when determining what is in the blood at that moment, while urine tests determine what is being flushed from the body, states Drug Detection Laboratories, Inc.
Blood testing is necessary for testing blood cell counts, deficiencies, cholesterol and glucose levels, according to Andrew Weil, M.D. For determining pregnancy, a urine test is usually done before blood testing as urine tests are 97 percent accurate, yet blood tests more accurately determine pregnancy earlier on, states American Pregnancy Association.
When drug testing, urine tests are more accurate than blood testing, as blood tests are positive only if the user is on the drug at the time of the test, according to Drug Detection Laboratories, Inc.