Anemia
Negative Coombs test<unk> 
Elevated LDH
Decreased haptoglobin
Positive sucrose lysis test or Ham test (both test sensitivity of RBCs to lysis by complement). Ham's test is when the patient's cells are incubated in acidified serum, which triggers the alternative compliment pathway, resulting in lysis of<unk>  cells. Sucrose lysis test is when the patient's serum is mixed in sucrose, which causes hemolysis of<unk>  cells.
Other clues: granulocytopenia/thrombocytopenia, venous thrombosis, aplastic anemia, MDS, dysphagia or abdominal pain
Flow cytometry of cell membrane proteins (CD55 and CD59) is a sensitive test for<unk>
Paroxysmal nocturnal hemoglobinuria
Disseminated Intravascular Coagulation 
Hereditary spherocytosis
Thrombotic Thrombocytopenic Purpura 
Myelophthistic anemia
Hemolytic Uremic Syndrome 
Thalassemia
HELLP syndrome