Your healthcare provider may ask that you have a repeat blood test when the results are invalid, to confirm unexpected results, or if not enough blood was provided to run all of the necessary tests. Blood is drawn in special tubes and transported to a lab for testing. The lab equipment requires a certain amount of blood to run the tests. Some lab tests are affected if the blood has sat in the tube for too long, if the tube was not maintained at the proper temperature, or if the blood underwent breakage (hemolysis) during the blood draw.