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FBC

Alternative Names
full blood count, complete blood count

Definition
A FBC, also called a full blood count, is a screening test used to diagnose and manage many diseases. A FBC measures the status of important features of the blood, including the:
  • number of red blood cells (RBCs)
  • number of white blood cells (WBCs)
  • number of platelets
  • total amount of haemoglobin in the blood
  • percentage of blood composed of cells, or haematocrit
  • mean corpuscular haemoglobin (MCH)
  • mean corpuscular haemoglobin concentration (MCHC)
  • mean corpuscular volume (MCV)
Who is a candidate for the test?
A FBC is a part of routine blood testing done with physical examinations. It is also used to help diagnose many disorders, including problems with a person's blood, heart, kidney and nutritional status.

How is the test performed?
A blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding.

What is involved in preparation for the test?
A person should request specific instructions from his or her doctor.

What do the test results mean?
Normal values are:
  • RBC (value changes with altitude): Male, 4.7 - 6.1 million cells/uL (cells per micro litre); female, 4.2 - 5.4 million cells/uL (cells per micro litre)
  • WBC: 4.0 - 11.0 thousand cells/uL (cells per micro litre)
  • haematocrit (varies with altitude): Male, 40.7-50.3%; female, 36.1-44.3%
  • haemoglobin (varies with altitude): Male, 135 - 180 g/L; female, 115 - 160 g/L
  • MCV: 80-98 femtolitre
  • MCH: 27-35 pg/cell
  • MCHC: 32-36 gm/dl
Abnormally high numbers of red blood cells may indicate:
  • low oxygen tension in the blood.
  • congenital heart disease, or a heart condition that a person is born with.
  • cor pulmonale, a condition in which the right lower part of the heart becomes swollen.
  • pulmonary fibrosis, or hardening of the lung tissue, which can make breathing difficult.
  • dehydration, or lack of fluid in the body. This can occur with conditions such as severe diarrhoea.
  • kidney disease with high erythropoietin production. Erythropoietin is a hormone made in the kidney.
Abnormally low numbers of red blood cells, or anaemia, may indicate:
  • blood loss
  • haemorrhage, or loss of blood
  • bone marrow failure
  • erythropoietin deficiency, which occurs when the kidney does not produce enough of the hormone
  • haemolysis, or the destruction of RBCs from a transfusion reaction
  • leukaemia, or cancer of the blood and bone marrow
  • multiple myeloma, a cancer of the bone marrow
  • malnutrition
  • over hydration, or absorption of too much fluid
Abnormally low numbers of white blood cells may indicate:
  • bone marrow failure
  • the presence of substances toxic to cells
  • collagen-vascular diseases, which are any diseases that cause the small blood vessels and tissue to swell
  • liver or spleen disease
  • exposure to radiation
High numbers of white blood cells may mean:
  • infections
  • inflammatory diseases
  • leukaemia
  • emotional or physical stress
  • tissue damage
High haematocrit may indicate:
  • dehydration.
  • burns.
  • diarrhoea.
  • eclampsia. Eclampsia is a serious condition involving high blood pressure, protein in the urine and swelling of the face and hands during pregnancy. It can lead to seizures and coma.
  • erythrocytosis, or an abnormal rise in the number of red blood cells.
  • polycythemia vera, or an increase in the cell mass or red blood cell levels in the blood.
  • shock.
Low haematocrit may indicate:
  • anaemia
  • blood loss
  • bone marrow failure
  • haemolysis, or the separation of haemoglobin, the oxygen-carrying component of red blood cells, from the red blood cells
  • leukaemia
  • malnutrition
  • specific nutritional deficiency
  • multiple myeloma
  • over hydration
  • rheumatoid arthritis, a long-term disease in which the connective tissue is destroyed
Low haemoglobin values may indicate:
  • anaemia
  • blood loss
Author: David T. Moran, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Contributors
Potential conflict of interest information for reviewers available on request


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