The Complete Blood Count (CBC) is a very common laboratory test. It examines our 3 types of blood cells: Red Blood Cells (RBCs), White Blood Cells (WBCs), & Platelets. See the links for more in-depth discussion.
In terms of RBCs, we’re usually dealing with Anemia (too few RBCs), but occasionally with Polycythemia (way too many). The CBC can also tell us the relative size of RBCs, which can clue us in to a variety of conditions, like Iron Deficiency, Vitamin B12 Deficiency, Liver Diseases, and genetic conditions that may pose risks for babies.
WBCs are of interest when we’re concerned about infection. The lab can count the number of the main types of WBCs, and their relative percentages. This can help us figure out if a person may have a bacterial vs. viral infection, and how bad a bacterial one might be (see Differences Among Germs). Very high WBC counts can also suggest Leukemia (blood cancer).
Platelets are what help our blood clot. So if there are way too many (“thrombocytosis”), there’s a risk of internal clotting, mainly a Stroke. If there aren’t enough (“thrombocytopenia”), there’s a risk of internal bleeding (& also a Stroke!). Low Platelets can also be a clue to undiagnosed Cirrhosis or HIV.