FINDING
DEFINITION · MECHANISM
CAUSES
CLUE
↓ production, ↑ destruction or sequestration; severe if < 500.
Chemotherapy, clozapine, methimazole/PTU, sulfa, carbamazepine; aplastic anemia; autoimmune; Felty syndrome; congenital (ELANE); benign ethnic neutropenia
Fever + sore throat on an antithyroid drug → agranulocytosis · G-CSF
Loss or redistribution of lymphocytes.
HIV, DiGeorge, SCID, steroids (lymphocyte apoptosis), SLE, radiation
Steroids also ↓ eosinophils
Marrow release (bands) or demargination (no bands).
Bacterial infection, tissue necrosis (MI), steroids, epinephrine/stress, smoking, asplenia
Left shift + toxic granulation + Döhle bodies = infection
Viral stimulation, blocked exit, or clonal growth.
Viral infections, EBV, CMV, pertussis (toxin blocks lymphocyte exit), CLL
Atypical lymphocytes in mono
Chronic stimulation of macrophage line.
TB, chronic infection, autoimmune disease, IBD, recovery from neutropenia, CMML
—
IL-5–driven production.
Invasive helminths, asthma/allergy, drugs (DRESS), Addison disease, Hodgkin lymphoma, EGPA; hypereosinophilic syndrome (PDGFRA)
Eosinophilia + hypotension + ↑ K⁺ → Addison
Clonal myeloid proliferation.
CML and other myeloproliferative neoplasms
Basophilia = think CML
Leukemoid reaction
reactive
Benign WBC rise > 50,000 from severe stress.
Sepsis, severe hemorrhage, burns, some tumors
Toxic granulation, ↑ LAP score, no BCR-ABL
Leukoerythroblastic reaction
Immature myeloid cells + nucleated RBCs released from a damaged marrow.
Marrow infiltration (metastases), myelofibrosis, severe hemolysis
Teardrop cells
Infectious mononucleosis
EBV
EBV infects B cells via CD21; CD8 T cells react → atypical lymphocytes.
Fever, pharyngitis, posterior cervical nodes, splenomegaly, hepatitis
Heterophile (Monospot) ⁺; rash with amoxicillin; no contact sports (splenic rupture)