Exams and Tests. Sickle cell disease is diagnosed when initial tests show abnormal hemoglobin, with more testing if needed. A sickle cell test looks for sickle cell trait and sickle cell disease.octors can diagnose sickle cell disease before a child is born (prenatally). Couples who are at risk for passing on this disease to their children may want to talk with a genetic counselor about prenatal testing. Prenatal tests include: 1  Amniocentesis.