Leukemoid reaction

Background

• Significant leukocytosis and neutrophilia in the absence of a hematologic malignancy
  • e.g. WBC ≥30-50 with ≥50% granulocytes

Differential Diagnosis

• Infections
  • Sepsis, pneumonia, urinary tract infection
  • Clostridioides difficile colitis (often quite high)
  • Disseminated tuberculosis
  • Severe shigellosis
  • Postpartum Clostridium sordellii
• Inflammation
  • Pancreatitis
  • Mesenteric inflammatory pseudotumor
• Malignancies
  • Carcinomas (lung, oropharyngeal, gastrointestinal, genitourinary)
  • Hodgkin lymphoma
  • Melanoma
  • Sarcoma
• Drugs
  • Corticosteroids
  • Minocycline
  • Recombinant hematopoietic growth factors
• Miscellaneous
  • Splenectomy
  • Ethylene glycol intoxication
  • Severe hemorrhage or acute hemolysis
  • Alcoholic steatohepatitis

Characteristic	Leukemoid reaction	Chronic myeloid leukemia	Chronic neutrophilic leukemia
Peripheral blood film	Mature neutrophils with a left shift	Immature cells, basophils, and eosinophils	Marked neutrophilia without immagure cells
LAP score	high	low	high
Vitamin B12	variable or high	high	high
Bone marrow	myeloid hyperplasia, orderly maturation, normal morphology	basophilia, eosinophilia, monocytosis, slight increase in blasts and reticulin fibrosis	myeloid hyperplasia, orderly maturation, normal morphology, but with packed bone marrow, slight increase in reticulin
Cytogeneic analysis	normal	BCR/ABL translocation	present in 35%
Serum G-CSF	high	low	low
Clonality studies	polyclonal	monoclonal	monoclonal

Further Reading

• Leukemoid reaction: Spectrum and prognosis of 173 adult patients. Clin Infect Dis. 2013;57:e177. doi: 10.1093/cid/cit562
• An update on the etiology and diagnostic evaluation of a leukemoid reaction. Eur J Internal Med. 2006 Oct;17(6):394-8. doi: 10.1016/j.ejim.2006.04.004