Additional 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.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.