Pregnancy, autoimmune diseases, an enlarged spleen and bacteria in the blood are reasons for a low platelet count, also known as thrombocytopenia. There are also a few medications that can contribute to low levels, including heparin, sulfa-containing antibiotics, quinine and interferon, explains Mayo Clinic.
In rare cases, a person may be diagnosed with thrombotic thrombocytopenic purpura, a disease that causes small blood clots to occur randomly within the body, as reported by Mayo Clinic. Patients who suffer from hemolytic uremic syndrome, military tuberculosis or a viral infection are also subject to low platelet levels, according to WebMD. In addition, patients who take chemotherapy medications or participate in radiation therapies are known to be diagnosed with thrombocytopenia. Blood cancer, bone marrow issues and vitamin B-12 deficiency can also cause low platelet counts.
Typically, a person's platelet levels range between 150,000 and 400,00 per microliter. Thrombocytopenia is diagnosed when a person's levels are lower than 150,000, states WebMD. Platelets are continuously renewed within the bone marrow, as noted by Mayo Clinic. Patients with thrombocytopenia tend to bleed more when injured, have blood mixed with urine or stool, bruise easily and more often than a healthy person, and experience bleeding into the skin.