Leukopenia refers to the decrease in the number of white blood cells (WBC) in blood. This may be caused due to certain medications, chemotherapy for cancer, radiation therapy for cancer, surgery, stem cell transplant, bone marrow transplant, steroids, cancer itself, some genetic conditions as well as autoimmune diseases. This is called immunosuppression as leukopenia leads to a weakened immunity.
Normal WBC counts
Leukopenia is caused due to decrease in number of WBCs, particularly neutrophils. For normal adult males the WBC counts range between 4500 and 11000 per cubic millimetre of blood. This is slightly higher in children.
Causes of Leukopenia
Leukopenia may be caused by various diseases and drugs. Some of these are outlined here:-
Bone marrow damage or suppression
This is caused due to exposure to certain chemicals or toxins, cancer chemotherapy, radiation therapy and certain drugs. These agents cause a decrease in production of all the cells of the bone marrow leading to leukopenia, anemia (low number of red blood cell production and platelets).
Bone marrow diseases
In these conditions the bone marrow does not produce sufficient WBCs or selectively produces excess of one type of WBCs leading to a lack of other types. The causes include myelodysplastic syndrome, leukemia, myeloproliferative syndrome, myelofibrosis (bone marrow replaced by fibrous tissues), vitamin B12 or folate deficiency etc.
Cancers that have spread to the bone marrow
Cancers when they have spread to the bone marrow may lead to leukopenia. This is seen in lymphomas and other cancers.
This occurs when the body fails to recognise its own cells and begins to attack them. In cases of leukopenia the body’s WBC’s are perceived as foreign and attacked. The condition is called lupus or Systemic lupus erythematosus (SLE).
Severe infections that deplete the body of WBCs may lead to leukopenia. This is called sepsis.
Diseases of the immune system
Diseases of the immune system, such as HIV, which destroy T lymphocytes
This is caused by enlargement of spleen that destroys the blood cells leading to leukopenia as well as anemia.
Other conditions like thyroid disorders (particularly over active thyroid glands), aplastic anemia, rheumatoid arthritis, parasitic infestations, vitamin deficiencies, mineral deficiencies of copper and zinc typhoid, malaria, influenza, dengue, Rickettsial infections, tuberculosis etc.
This occurs at the initial phases of the infection. The leukocytes (predominately neutrophils) are responsible for the initial reaction to an infection. After an infection these cells gather around the margins of the blood vessels (marginalized) so that they can scan for the site of infection. Thus there is increased WBC production but it appears low from a blood sample, since the blood sample is of core blood and does not include the WBCs gathered to reach the site of infection.
Drugs causing leukopenia
Some drugs may lead to leukopenia. Medications which can cause leukopenia include:
- clozapine, an antipsychotic medication
- sodium valproate and lamotrigine - antiepileptic agents
- immunosuppressive drugs, such as sirolimus, mycophenolate mofetil, tacrolimus, and cyclosporine that are used in transplant patients
- interferons used in treatment of multiple sclerosis etc.
The antidepressant and smoking addiction treatment medication called Bupropion and antibiotic Minocycline and penicillin may also cause leukopenia.
The mechanism of leukopenia caused by drugs is mainly mediated by the immune system itself. Some agents like cancer chemotherapy drugs however cause leukopenia by suppressing the bone marrow.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)