White blood cells (WBCs) or leukocytes form part of the body’s immune system and help defend the body against infection. They are characterized as granulocytes or agranulocytes. There are three types of granulocytes – neutrophils, eosinophil and basophils, and two types of agranulocytes – monocytes and lymphocytes.
Normal range of WBC count is 4000 – 11000 cells/ cu mm. A value above 11000 is termed as leukocytosis and a value less than 4000 is termed as leukopenia. A slightly elevated count can also be seen in pregnancy or in children below the age of 2 years. WBC counts are high during an infection. A very high count could indicate leukaemia. Increased neutrophil count could indicate a bacterial infection and elevated levels of lymphocytes could indicate a viral infection. Eosinophil levels are increased in allergies or parasitic infection. Low levels of WBCs are commonly seen in people on steroid or cancer medications. Low WBC levels could also indicate a malfunctioning of the bone marrow.