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Blood, the liquid connective tissue of our body is composed of red blood cells (RBCs), white blood cells (WBCs) and platelets suspended in a liquid component called plasma. The cellular and non-cellular components of blood together play an important role in several immune system processes of the body.

Immature WBCs or leukocytes are produced from precursor cells by a process called hematopoiesis, that occurs in the bone marrow. Some of the immature WBCs differentiate to maturity in the bone marrow itself, and then released into the bloodstream; whereas some are released into the blood stream directly and further undergo maturation in different tissues. All the different types of WBCs, namely granulocytes like basophils, eosinophils and neutrophils as well as agranulocytes that include lymphocytes, dendritic cells, monocytes and macrophages form the most important set of our immune system.

The total count of all these WBCs, under normal conditions, ranges between 4,000 and 10,000 per microliter of blood. Leukopenia or low WBC count is characterized by values below 4000 per microliter. Such low white blood cell counts can be the result of a nutritional deficiency, certain infections, diseases that affect the bone marrow, autoimmune disorders, as well as certain chemotherapeutic agents. Low WBC count weakens the immune system and leads to an increased risk of infections.

Causes
Reduction in the number of WBCs in blood may occur due to defects in hematopoiesis or altered survival of immature and mature WBCs. In most cases leukopenia is a result of low neutrophil count (neutropenia), and rarely due to reduced lymphocytes (lymphocytopenia). These conditions may occur due to the following factors.

Malnutrition
Mineral and vitamin deficiencies as well as certain types of anemia affect the production and maturation of WBCs, thereby leading to a reduction in their levels in blood. Deficiency of zinc, copper as well as pernicious anemia that arises due to deficiency of vitamin B12 may lead to reduction in the number of neutrophils, thereby causing low WBC count.

Infection
The pathogenesis of certain viruses and bacteria leads to leukocyte damage resulting in a rapid reduction of WBC counts within the first two days after infection. Such leukopenia may persist for three to seven days, and is characteristic feature of viral hepatitis, smallpox, typhoid, rickettsial infections as well as cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections. AIDS is characterized by a similar reduction in WBC count (especially T-lymphocytes) that occurs during 6-12 weeks after infection. This phase is followed by an increase in leukocyte count, but not up to the normal levels. Leukopenia persists as the viral load keeps on increasing.

Autoimmune Disorders
Certain autoimmune disorders are characterized by the destruction of the hematopoietic stem cells as well as mature leukocytes. These include systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and celiac disease.

Hypersplenism
The spleen is responsible for destruction of old and damaged blood cells. Hypersplenism refers to a condition characterized by an over-active spleen leading to early destruction of blood cells. As a result the overall blood count reduces. In addition to leukopenia, other signs and symptoms include splenomegaly (enlarged spleen) as well as abdominal pain and fullness. Hypersplenism is observed in case of liver cirrhosis, malaria, Gaucher's disease, Felty's syndrome and sarcoidosis.

Myelodysplastic Syndromes (MDS)
Conditions that involve damage or defects in the myeloid cells (blood forming cells present in bone marrow) are collectively referred to as myelodysplastic syndrome (MDS) or preleukemia. In many cases, the cause for MDS cannot be identified, and the individuals are often asymptomatic in the early stages. The condition gets diagnosed serendipitously during routine blood tests or while investigation of some other disease or condition. However, symptoms like easy tiring and fatigue, general malaise, shortness of breath, easy bruising etc. may indicate the presence of MDS.

Cancers
Although blood and bone marrow cancers are characterized by an increase in production of white blood cells, those which cause uncontrolled proliferation of immature cells lead to leukopenia. This is because the increase in such abnormal immature cells results in crowding, and limits the normal growth of white blood cells. As a result the number of white blood cells circulating in blood is low. Examples include multiple myeloma, acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML) and certain lymphomas. The lineage and maturation stage of the abnormal cell determines the outcome as far as the proliferation of other white blood cells is concerned, leading to leukopenia or leukocytosis (high WBC Count).

Medication
Leukopenia may occur as a side effect of immunosuppressive drugs, nonsteroidal anti-inflammatory drugs (NSAID) as well as chemotherapy and radiation therapy, especially in case of leukemia treatment. These drugs affect the proliferation of blood cells in bone marrow, thereby leading to a decline in the white blood cell count. Examples include azathioprine, cyclophosphamide, phenothiazine derivatives, etc. However, the occurrence of leukopenia depends on the precise combination and dosage of drugs.

Effects and Symptoms
White blood cells are responsible for immunity against infectious agents, and form an important part of the protective army of our body. Being so, low WBC count leads to an increased susceptibility to infections. Recurrent viral sinusitis and flu, bacterial infections as well as delayed recovery are characteristic symptoms of weakened immune system, and hence may be suggestive of the early stages of leukopenia. Infections in the gastrointestinal system, lungs, throat and bladder are some typical examples.

The lower the WBC count, higher is the risk of infections. As per the James Cancer Hospital & Solove Research Institute, the risk of infection with respect to decrease in number of WBCs and neutrophils (per microliter of blood) is as given below.

WBC Count
(per μL of blood)
ANC
(per μL of blood)
Risk of Infection
10,0005000Normal
5,0002,500Low
2,0001,000Moderate
1,000500High
WBC: White Blood Cells; ANC: Absolute Neutrophil Count

Treatment
Blood test for a complete blood count with differential is essential to identify low WBC counts. In addition, other investigations and bone marrow examination may be advised to understand the precise etiology. The treatment depends on the underlying condition or disorder that results in leukopenia.

However, some common treatment options include the use of growth factors that stimulate production of white blood cells. Examples include filgrastim and pegfilgrastim. In addition, antibiotic and antiviral agents may be prescribed in case of infections.

In case of chemotherapy-induced leukopenia, growth factors may be prescribed as well as adjustments in chemotherapy doses and frequency may be advised. However, the precise set of drugs depends on the type of cancer, severity, as well as the type of white blood cells reduced.

Precautions
Individuals suffering from leukopenia need to take extra precautions with respect to hygiene, diet as well as when interacting with others, since they are more susceptible to infections, and may not recover from them easily. Some of the food safety recommendations given by USDA (The United States Department of Agriculture) are as follows:

Consume pasteurized juices and dairy products.
Wash hands with warm soapy water before handling and eating food.
Keep the cutting and preparation surfaces clean by washing them often with warm water.
Use different cutting boards for raw meats and vegetables or fruits, to avoid cross-contamination of vegetables.
Cook meat/meat products to appropriate temperatures, and bring sauces, soups, and gravy to a boil when reheating.
Refrigerate meat, poultry, eggs, seafood, and other perishables within 1-2 hours of cooking or purchasing.
Store foods and beverages in carefully wrapped containers to avoid spillage into other food items.

Disclaimer: This Buzzle article is for informative purposes only, and should not be used as a replacement for professional medical advice.