Increased basophils may be associated with some myeloid neoplasms such as CML, or some infections or some hypersensitivity reactions.
Basophils and Mast cells are distinct from one another but share some similar morphologic and functional aspects. As opposed to basophils which can be seen in the peripheral blood, mast cells are only seen in tissue and absent from the peripheral blood.
Additionally, the nucleus of the mast cell is usually round and not segemented as opposed to the basophils' segmented (usually bi-lobed) nucleus. The granules of basophils are more heterogenous and overlap the nucleus while the granules of mast cells are more uniform and less often cover the nucleus. (For more details, please see the mast cell entry under the Glossary section.)