Hello, Welcome to HCM. I understand your concern regarding enlargement of spleen of your daughter and the huge blood clots on her periods. Spleen s main function is to act as a filter for your blood. It recognizes and removes old, malformed, or damaged red blood cells. When blood flows into your spleen, your spleen performs quality control ; your red blood cells must pass through a maze of narrow passages. Healthy blood cells simply pass through the spleen and continue to circulate throughout your bloodstream. Blood cells that can t pass the test will be broken down in your spleen by macrophages. Macrophages are large white blood cells that specialize in destroying these unhealthy red blood cells. Your daughter must get immediate medical attention to rule out any infection which causes her spleen to enlarged and blood clots could be due to initiation of periods. Consult physician and gynecologist respectively for further clinical assessment. Regards,