CBC is a numerical report of all blood elements, as well as a description of some of their major characteristics. Most laboratories use automated counters. The CBC reports include RBC count, WBC count, platelet count, Hb, Hct (volume of packed red cells), mean platelet volume, and other parameters (described under individual tests). The CBC may be ordered as a simple count of blood elements and RBC indices or as a test that includes a WBC differential.
Use
CBC is used for screening whenever abnormalities in RBCs, WBCs, or platelets are suspected.
New analyzers may separate reticulocytes and platelets into young and mature populations that help detect bone marrow regeneration. Automated counters flag abnormalities in RBCs, WBCs, and platelets, triggering examination of the peripheral blood smear.
Limitations
Proper specimen collection is required for reliable and accurate reporting of the CBC. Misleading results occur if the specimens contain clots, if the blood is not properly mixed, or in the presence of agglutinated RBCs. Specific pitfalls are described under each lineage.