LEUCOCYTES or white blood cells are the main defence of the body against infection by bacteria and other micro-organisms. These are larger in size compared to red blood cells while their number is smaller. Every micro litre of blood contains between 4000 to 11000 white blood cells in a normal person. A fall of their number below 4000/ul is considered as 'low white blood cell count' or 'LEUCOCYTOPENIA.'
White blood cells include five different types of cells.
(i) NEUTROPHILS - These make up about 40 to 45% of all white blood cells. They are the most active in defending against invading bacteria. So their number increases in most acute bacterial infections. In chronic or long term infections like Tuberculosis or leprosy, their role is far less. A fall in their number is called NEUTROPENIA.
(ii) EOSINOPHILS - These amount to 1 to 6 % of white blood cells. They are found at the sites of entry of foreign materials, like the gut wall, skin, and lining of the respiratory tract. Their primary function is that of detoxification. They have an affinity for histamine and are attracted by its release.
(iii) LYMPHOCYTES - The lymphocytes make up 20 to 45 % of white blood cells. They give rise to the PLASMA CELL as a reaction to immune needs. Their main function pertains to production of ANTIBODIES that are used for killing foreign cells and bodies, in order to destroy and digest them.
(iv) MONOCYTES - These are about 2 to 6 % of all white blood cells, and they have the ability to kill and digest foreign particles to save body from them, and are crucial for removing larger particles.
(v) BASOPHILS - These make up less than a percent of all white blood cells. They contain histamine and heparin and cause their release which attracts other white blood cells.
CAUSES OF LOW WHITE CELL COUNT
A reduction in number of white blood cells can be caused by a number of conditions. The most common of them are described here.
1. BONE MARROW SUPPRESSION - White blood cells are formed in the bone marrow. Their production can result from suppression of bone marrow as in MYELOFIBROSIS - a condition where bone marrow tissue is replaced by fibrosis; Other causes of suppression include RADIOTHERAPY or CHEMOTHERAPY for treating cancers; APLASTIC ANEMIA - where all cell production is decreased because of different known or unknown causes. In some cases of blood cancer or LEUKEMIA, the cancerous cells cover and occupy the whole of bone marrow thereby interfering with formation of white blood cells.
2. INFECTIONS - TYPHOID, INFLUENZA : These are some of the most common causes of low white blood cells, and are usually reversed after the remission of the infection. It can also be due to Rickettsial infection in some cases. Other infections include Dengue fever and Tuberculosis.
3. AUTO-IMMUNE DISEASES - SYSTEMIC LUPUS ERYTHEMATOSUS: Auto-immune diseases like Lupus involve a condition where the body immunity consisting of white blood cells start attacking body parts. In the process, the white cell count also falls in addition to damage to different parts of body.
4. MEDICATIONS - The most common culprits that lead to fall in white cell counts are IMMUNOSUPPRESSIVE DRUGS like SIROLIMUS, MYCOPHENOLATE and TACROLIMUS are used in auto-immune diseases or allergies. Other drugs include CLOZAPIN, an antipsychotic medicine. SULPHONAMIDES can also sometimes cause this condition.
5. MINERAL DEFICIENCY - COPPER, ZINC DEFICIENCY: Deficiency of copper and zinc, which are important trace elements in nutrition, is also associated with low white blood cell counts.
6. OTHERS - Many other not so common conditions like Bracken fern poisoning can also cause a fall in white blood cells.
IDENTIFYING THE CAUSE
Total leukocyte count is a blood test frequently to get clues about the disease. When it reveals a low white cell count, it indicates a need for further investigations and analysis of the clinical picture to make a diagnosis of the medical condition causing the fall in white cell count.