How is it used?
The FBC is used as a broad screening test to check for such disorders as anaemia, infection, and many other diseases. It is actually a panel of tests that examines different parts of the blood and includes the following:
- White blood cell (WBC) count is a count of the actual number of white blood cells per volume of blood. Both increases and decreases can be significant.
- White blood cell differential: looks at the types of white blood cells present. There are five different types of white blood cells, each with its own function in protecting us from infection. The differential classifies a person’s white blood cells into each type: neutrophils (also known as PMNs), lymphocytes, monocytes, eosinophils, and basophils.
- Red blood cell (RBC) count: is a count of the actual number of red blood cells per volume of blood. Both increases and decreases can point to abnormal conditions.
- Haemoglobin measures the amount of oxygen-carrying protein in the blood.
- Haematocrit measures the amount of space red blood cells take up in the blood. It is reported as a percentage (0 to 100) or a proportion (0 to 1).
- The platelet count is the number of platelets in a given volume of blood. Both increases and decreases can point to bleeding or bone marrow disorders.
- Mean platelet volume (MPV) is a machine-calculated measurement of the average size of your platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced.
- Mean corpuscular volume (MCV) is a measurement of the average size of your RBCs. The MCV is elevated when your RBCs are larger than normal (macrocytic), for example in anaemia caused by vitamin B12 deficiency or folic acid deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic), which may indicate iron deficiency anaemia, inflammation or occasionally thalassaemias.
- Mean corpuscular haemoglobin (MCH) is a calculation of the amount of oxygen-carrying haemoglobin inside your RBCs. Since macrocytic RBCs are larger than either normal or microcytic RBCs, they would also tend to have higher MCH values.
- Mean corpuscular haemoglobin concentration (MCHC) is a calculation of the concentration of haemoglobin inside the RBCs. Decreased MCHC values (hypochromia) are seen in conditions where the haemoglobin is abnormally diluted inside the red cells, such as in iron deficiency anaemia, long standing inflammation or thalassaemia. Increased MCHC values (hyperchromia) are seen in conditions where the haemoglobin is abnormally concentrated inside the red cells, such as in hereditary or autoimmune spherocytosis.
- Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anaemias, such as iron deficiency or pernicious anaemia, the amount of variation (anisocytosis) in RBC size (along with variation in shape – poikilocytosis) causes an increase in the RDW.
Anaemia, such as fatigue or weakness, or has an infection, inflammation, bruising, or bleeding, then the doctor may order a FBC to help diagnose the cause. Significant increases in WBCs may help confirm that an infection is present and suggest the need for further testing to identify its cause. Decreases in the number ofRBCs (anaemia) can be further evaluated by changes in size or shape of the RBCs to help determine if the cause might be decreased production, increased loss, or increased destruction of RBCs. A platelet count that is low or extremely high may need further investigation. Many conditions will result in increases or decreases in the cell populations. Some of these conditions may require treatment, while others will resolve on their own.
Some diseases, such as cancer (and chemotherapy treatment), can affect bone marrow production of cells, increasing the production of one cell at the expense of others or decreasing overall cell production. Some medications can decrease WBC counts, and some vitamin and mineral deficiencies can cause anaemia. The FBC test may be requested by the doctor on a regular basis to monitor these conditions and drug treatments.
What does the test result mean? The following table explains what increases or decreases in each of the components of the FBC may mean.
Is there anything else I should know?
Many different conditions can result in increases or decreases in the cell populations. Some of these conditions may require treatment, while others may resolve on their own. Recent blood transfusions affect the results of the FBC. Normal FBC values for babies and children are different from adults. The laboratory will supply the reference ranges for various age groups, and a healthcare professional will take these into consideration when interpreting data.