5. Leucocytes or WBCs
Which is the number of white blood cells per cubic milliliter, it is indicative of the state of the immune system. Generally speaking, an increased WBCs count -also termed leukocytosis- means that the body is fighting something, be it bacteria, viruses, fungi, parasites, or tumor cells. Decreased WBCs count, on the other hand, indicates an immune deficiency, whether due to primary affection of the bone marrow or as a reaction to some bacterial and viral infections. It can also occur in some tumors whether those arising from the bone marrow cells or others that appeared elsewhere and spread -or metastasized- to the bone marrow.
White blood cells are then differentially counted according to their main subtypes, this is done by the help of a microscope and blood film with special stains, the primary normal white blood cells are:
Neutrophils form most WBCs with a ratio ranging from 54-62%. Neutrophils are one of the first-line defenses against any offending agent entering the body and are generally increased in cases of bacterial infections and decreased in immune deficiency states namely: HIV infection, bone marrow failure and prolonged immunosuppressive drug therapy.
Lymphocytes are the second most abundant white blood cells with a ratio of 25-32%. Their level is elevated in viral infections and some cancers and decreased in immune deficiency.
They form 1-3% of WBCs in a healthy human, but they may be elevated in some allergic conditions and parasitic infestations.
They also form less than 1% of WBCs, but they may be elevated in some infections, such as smallpox and cancer.