Does thrombocytopenia occur in all cases of pre-leukemia or leukemia?

No. The effect on the blood counts such as the white blood cells, red blood cells and platelets can be variable. The platelets can be low (thrombocytopenia) for these disorders but in some patients it can be normal.

No. Some leukemias, e.g. Chronic myelogenous leukemia may have elevated platelet count.