The FBC is used as a broad screening test to check for such disorders as anaemia, infection, and many other diseases.
If a patient is having symptoms associated with 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 of RBCs (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.