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Leukemoid reaction
Other Resources UpToDate PubMed

Leukemoid reaction

Contributors: Michael W. Winter MD, Paritosh Prasad MD
Other Resources UpToDate PubMed


A leukemoid reaction is a leukocytosis exceeding 50 000/µL due to a cause other than leukemia. This is typically characterized by elevated neutrophils, indicative of an acute inflammatory process, and the absence of dysplastic cells suggestive of a hematologic malignancy. Coinciding with a marked increase in leukocytes is the presence of neutrophil precursor cell types: myelocytes, metamyelocytes, and promyelocytes.

Leukemoid reactions occur in a variety of different conditions, all indicative of acute stress. These include infectious etiologies, adverse reactions to medications, asplenia, diabetic ketoacidosis, and septic shock with end-organ damage. Infants with trisomy 21 can often be born with a leukemoid reaction.

Leukemoid reactions will resolve with treatment of the underlying condition.


D72.823 – Leukemoid reaction

56478004 – Leukemoid reaction

Look For

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Hematologic malignancy – Peripheral smear will reveal dysplastic cell types.
  • Infection – Tuberculosis, Clostridioides difficile colitis, Pertussis, and Mononucleosis from Epstein-Barr virus are most commonly associated with a leukemoid reaction. Visceral Cutaneous larva migrans can cause a leukemoid reaction but is associated with prominent eosinophilia.
  • Asplenia
  • Ischemic hepatitis (see Acute liver failure)
  • Ischemic colitis
  • Diabetic ketoacidosis
  • Toxin ingestion or adverse drug reaction – Glucocorticoids, all-trans retinoic acid, dapsone, sulfa drugs, and ethylene alcohol intoxication are common causes.
  • Paraneoplastic syndrome
  • Acute blood loss anemia with hypovolemic shock – Retroperitoneal hemorrhage, gastrointestinal hemorrhage, trauma.
  • Down syndrome – Newborn with leukemoid reaction on routine blood work.

Best Tests

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Management Pearls

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Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

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Last Reviewed:02/03/2019
Last Updated:10/31/2022
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Leukemoid reaction
A medical illustration showing key findings of Leukemoid reaction : Leukocytosis, Neutrophilia
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