Leukemoid Reaction

Sample blood for leukemoid reaction

• Blood in EDTA is needed, along with a fresh blood smear.

Definition of Leukemoid Reaction

1. If there is a persistent increase in the neutrophils, reactive and excessive leucocytosis with a count of 30,000 to 50,000 / µL, with immature and mature white cells in the peripheral blood smear is called Leukemoid reaction. Sometimes lymphocytic reactions may be seen.
2. This is not a primary marrow disorder, and this is due to secondary infections.
3.   The count varies from 50,000 to 100,000/cmm. with the presence of immature cells.
4. Blast cells in the peripheral blood smears are not seen, which helps differentiate from leukemia.
5. Extremely elevated counts >100,000/cmm are more suggestive of the myeloproliferative process, with some exceptions.

Types of leukemoid reaction:

1. Neutrophilic reaction.
2. Lymphocytic reaction.
3. Monocytic reaction.

Significance of leukemoid reaction

1. This term is used to differentiate between leucocytosis and leukemia.
2. In leukocytosis or neutrophilia, there is an increase in the count from 10,000 to 25,000 / µL (microliter).

Pathogenesis of leukemoid reaction:

1. Leucocytosis results from the release of the cells from the bone marrow under the influence of IL-1 and TNF.
2. There is a shift to the left of the neutrophils.
3. Prolonged infection induces in the bone marrow the proliferation of the precursor cells, and that is also produced by the cytokines like  IL-1 and TNF.
4. Bacterial infections induce a selective increase in the neutrophils, while parasitic infestation induces eosinophilia.
5. Mumps, Rubella, and some viruses lead to a selective increase in the lymphocytes and cause lymphocytosis.

The differentiating point from leukemia:

1.  In the leukemoid reaction, the neutrophils are mature and not clonally derived.
2. There is a persistent increase in TLC above 50,000/cmm and no evidence of leukemia.
3. Blood count comes to normal after treating the cause.
4. Increased blast cells are not seen in the leukemoid reaction.
5. A count above 100,000 /µL is more suggestive of the myeloproliferative disorder with very few exceptions.
6. Granulocytes show toxic granulations and Dohle bodies.
7. NAP score is high, which is low in leukemia.
8. Leukemoid reaction shows:
   1. Toxic granulations.

1. 2. Toxic vacuolization.
   3. Presence of Dohle bodies. These are light blue to grey, oval, and basophilic inclusions in the neutrophils. Usually seen in the peripheral area of the cytoplasm of neutrophils. These consist of ribosomes and endoplasmic reticulum.

Differential diagnosis includes:

1. Chronic myeloid leukemia.

Causes of Leukemoid reaction (Neutrophilic type):

1. A severe infection:
   1. Septicemia.
   2. Clostridium.
   3. Tuberculosis.
   4. Pertussis.
   5. Infectious mononucleosis.
   6. Endocarditis.
   7. Pneumonia.
   8. Tuberculosis.
2. Toxic conditions:
   1. Eclampsia.
   2. Burns.
   3. Mercury poisoning.
3. Parasitic infestation:
   1. Larval migration leads to eosinophilia.
4. Leukemoid lymphocytosis:
   1. It is seen in Tuberculosis, Whooping cough, and infectious mononucleosis.
5. Malignancy:
   1. Carcinoma of the colon.
   2. Embryonal carcinoma of kidneys.
6. Miscellaneous causes:
   1. Severe hemorrhage.
   2. Acute hemolysis.
   3. Diabetic ketoacidosis.
   4. Ischemic colitis.
   5. Hepatic necrosis.
7. Drugs:
   1. Like Sulfa, Dapsone, Glucocorticoids, and the G-CSF factor.

Lymphocytic leukemoid reaction is seen in:

1. Infections:
2. Infectious mononucleosis.
3. Pertussis.
4. Varicella.
5. Tuberculosis.
6. Malignancies:
   1. Carcinoma of the stomach.
   2. Carcinoma of the breast.
7. Others like Dermatitis herpetiformis.

Monocytic leukemoid reaction:

1. It is seen in tuberculosis.

Difference between Leukemoid reaction and chronic myelocytic leukemia: