Leukemoid reaction D72.8

A leukemoid reaction is defined as a white blood cell count greater than 50 × 10 / µl (Sene 2021).

It represents an excessive reactive leukocytosis (Hoffbrand 2003), resulting in a pronounced, reactive left shift with the detection of immature myeloid cells, including blasts, in the peripheral blood, without evidence of chronic myelosis (Baum 2018).

In the case of a leukemoid reaction, a distinction is made between:

• Myeloid leukemoid reaction:

This reaction can occur in cases of sepsis, chronic infections, or during treatment with G-CSF. Occasional mild splenomegaly may be present. Laboratory findings include white blood cell counts < 100,000 / µl, no basophils, rarely myeloblasts, and a marked left shift with toxic granulation (Herold 2025).

• Lymphocytic leukemoid reaction:

This is seen in pertussis or certain viral infections and is characterized by high lymphocyte counts (Herold 2025).

A leukemoid reaction is a rare hematological disorder (Hussein 2023) that can occur in the context of severe acute and chronic infections. It is more common in children (Antwerpes 2019).

• Presence of circulating neutrophils that are mature but do not originate from a clonal source (Kasper 2015)
• marked leukocytosis with white blood cell counts > 50,000 cells/µl. If white blood cell counts are within the normal range or even reduced, this indicates exhaustion of leukopoiesis (Antwerpes 2019)

• Leukemia:

In contrast to a leukemoid reaction, this condition is characterized by an increase in basophils and elevated levels of alkaline leukocyte phosphatase. Additionally, a hiatus leucaemicus is present (Scheurlen 1982).

• Other neoplasms of the hematopoietic system (Antwerpes 2019)
• Paraneoplastic leukemoid reaction (Portich 2020)

1. Antwerpes, F., & Vehring, M. (2019). Leukemoid reaction. Doc Check Flexikon https://flexikon.doccheck.com/de/Leuk%C3%A4moide_Reaktion
2. Baum H (2018) Leukemoid reaction. https://www.springermedizin.de/emedpedia/detail/lexikon-der-medizinischen-laboratoriumsdiagnostik/leukaemoide-reaktion?epediaDoi=10.1007%2F978-3-662-49054-9_1857
3. Herold, G., et al. (2025) Internal Medicine. Herold Verlag 103
4. Hoffbrand A V, Pettit J E, Moss P A H, Hoelzer D (2003) Introduction to Hematology. Blackwell Verlag Berlin 121
5. Hussein T W, Almualem Z D, Almualem F D, Zainaldeen B A, Alshaikkh Z J (2023) Leukemoid Reaction With Severe Diabetic Ketoacidosis. *Cereus*. 15 (12) e:50325
6. Kasper D L, Fauci A S, Hauser S L, Longo D L, Jameson J L, Loscalzo J et al. (2015) Harrison’s Principles of Internal Medicine. McGraw-Hill Education 418–419
7. Portich J P, Faulhaber G A M (2020) Leukemoid reaction: A 21st-century cohort study. Int J Lab Hematol. 42 (2) 134–139
8. Scheurlen P G (1982) Systematic Differential Diagnosis of Internal Diseases. Springer Verlag Berlin / Heidelberg / New York 25
9. Sene D R, Watashi D M (2021) Leukemoid Reaction in a Severe COVID-19 Patient. Cureus 13 (9) e17865