Leukemia literally means 'many white cells in the blood'. The white cells are part of the body's immune system, and there are several sub-groups of white cells that have different sorts of roles in recognizing and dealing with 'invaders' such as bacteria and viruses as well as other types of foreign protein. All of the blood cells originate in the bone marrow and leukaemia which is also known as blood cancer is a disease where the bone marrow produces large numbers of abnormal white cells.

Leukemia is a general term for four different types of blood cancer. There are two types of acute leukemia and two types of chronic leukemia. It begins in the bone marrow when one cell changes and becomes a leukemia cell. This cell multiplies and eventually the normal blood cells are crowded out. The abnormal cells then spill over into the blood and may also invade the central nervous system.

Acute leukemia is a form of cancer that develops very rapidly. It is manifested through overpopulation of the blood with immature cells that are unable to fulfill the functions of normal blood cells. In the case of acute leukemia, the marrow is unable to produce normal quantities of red blood cells, white blood cells and platelets. Patients who suffer from leukemia also develop anemia, a deficiency of normal red blood cells. Also, a decreased number of white blood cells reduces the body’s ability of overcoming infections, while the lack of platelets facilitates inflammation and bleeding.

Leukemia leads to the accumulation and crowding of diseased stem cells at the level of the bone marrow, which decreases the normal production of healthy blood cells. The lack of normal blood cells leads to the appearance of leukemia symptoms. It is important to understand that despite the fact that leukemia causes an over production of white blood cells, these cells are immature and can’t substitute for normal blood cells. Due to this, the body is exposed to many forms of infection.

Once leukemia is suspected, physicians often recommend further testing for confirmation purposes. For leukemia, the most common test is a blood test, wherein any abnormalities related to leukemia can be seen. One of these abnormalities is anemia, which means that the blood has very low levels of erythrocytes or red blood cells; unusual paleness of the patient and a certain level of respiratory difficulty often characterize this condition. Another abnormality is Leukopenia, which means that the blood has very low levels of leukocytes or white blood cells, which increases the risk of infection in the patient.

The causes of all types of leukemia are unknown, doctors cannot determine why some people have this illness and other don't. Though, scientists discovered some factors that increase the risks of becoming ill of leukemia. Among these factors radiations play an important role, many that were exposed to radiations were soon diagnosed with leukemia. Also, a malfunction in the genes can cause the blood cells to transform, so it can have a genetic cause. The causes and risk factors are still being researched.

All kinds of various acute or chronic diseases of leukemia are dangerous. Acute leukemia being a swiftly succeeding disease affects typically cells that are embryonic or primitive (which means the cells that have not yet fully developed or differentiated from the others). These not fully formed cells thus cannot achieve their standard utility. These cells are described as "nonfunctional" because they do not work like normal cells. They also number out the usual normal healthy cells in the marrow, resulting in a decrease in the number of new healthy normal cells made in the marrow.