Hypereosinophilic syndrome (HES): This condition is characterized by the overproduction of eosinophils, which can also lead to an increase in other myeloid cells like monocytes and basophils due to the underlying bone marrow response and cytokine dysregulation.

Parasitic infections: Certain parasitic infections can cause an increase in eosinophils, and in some cases, may also affect monocyte and basophil counts due to the body's immune response.
Allergic reactions: Severe allergic reactions can lead to an elevation in eosinophils and, to a lesser extent, basophils. Monocytes may also be elevated as part of the inflammatory response.
Myeloproliferative neoplasms (MPNs): Conditions like chronic myeloid leukemia (CML) or other MPNs can lead to an increase in various myeloid cell lines, including monocytes, eosinophils, and basophils.

Leukemia (especially acute myeloid leukemia, AML): Although less common, certain types of leukemia can present with an elevation in multiple myeloid cell lines. Missing this diagnosis could be catastrophic.
Systemic mastocytosis: This condition involves the proliferation of mast cells and can lead to an increase in basophils and, occasionally, eosinophils and monocytes. It's crucial to consider due to its potential for severe complications.

Chronic eosinophilic leukemia: A rare myeloproliferative disorder characterized by the clonal proliferation of eosinophils, which can also affect other cell lines.
Mast cell leukemia: An extremely rare condition that could potentially lead to an elevation in basophils and other myeloid cells.
Lymphoma: Certain types of lymphoma, particularly those involving the bone marrow, can lead to reactive changes in myeloid cell lines, including elevations in monocytes, eosinophils, and basophils.