Tests and diagnosis. A blood test can check for hemoglobin S â the defective form of hemoglobin that underlies sickle cell anemia. In the United States, this blood test is part of routine newborn screening done at the hospital.But older children and adults can be tested, too.In adults, a blood sample is drawn from a vein in the arm.dditional tests. To confirm any diagnosis, a sample of blood is examined under a microscope to check for large numbers of sickle cells â a marker of the disease. If you or your child has the disease, a blood test to check for anemia â a low red blood cell count â will be done.