Neutrophils, lymphocytes, eosinophils, monocytes and basophils
Expansion
Neutrophilia: bacterial infection, tissue damage, infarction, burns, corticosteroids, lithium, exercise, stress, smoking, pregnancy, myeloproliferative disease, malignancy.
Neutropenia: viral infection, drugs (carbimazole, clozapine, chemotherapy, sulphasalazine), autoimmune, marrow failure, B12 and folate deficiency, hypersplenism, severe sepsis, and benign ethnic neutropenia, which is common in people of African ancestry and needs no investigation.
Lymphocytosis: viral infection, particularly Epstein-Barr virus and cytomegalovirus, chronic lymphocytic leukaemia in the older patient, pertussis, toxoplasmosis, tuberculosis, post-splenectomy.
Lymphopenia: steroids, HIV, chemotherapy, radiotherapy, sepsis, lymphoma, systemic lupus erythematosus, malnutrition, and acute severe infection including influenza and COVID-19.
Eosinophilia, remembered as the causes beginning with A: Allergy and asthma, Addison’s, Aspergillosis, and then parasites (helminths, not protozoa), drugs, Churg-Strauss (eosinophilic granulomatosis with polyangiitis), skin disease, and haematological malignancy.
Monocytosis: chronic infection including tuberculosis and endocarditis, inflammatory bowel disease, chronic myelomonocytic leukaemia, recovery from neutropenia.
Basophilia: chronic myeloid leukaemia and the myeloproliferative disorders, and it is otherwise rare enough to be a useful pointer.
Left shift means immature granulocytes in the blood, indicating marrow stress. A leukaemoid reaction is a marked neutrophilia over 50 with a left shift from severe infection, and is distinguished from chronic myeloid leukaemia by a high leucocyte alkaline phosphatase and the absence of the Philadelphia chromosome.