Complete blood count (CBC) is a basic comprehensive laboratory test. The service includes an automated complete blood count with a white blood cell differential and determination of the erythrocyte sedimentation rate (ESR). The test helps assess the number and characteristics of the main blood cell types and identify changes that may accompany anemia, infectious, inflammatory, and other diseases.
Among laboratory tests, the complete blood count is one of the basic tests. CBC provides information about red blood cells, white blood cells, and platelets. This test is also referred to as a 'clinical blood count' or 'complete clinical blood count'.
Red blood cells carry oxygen, white blood cells are involved in immune defense, and platelets help stop bleeding. Changes in the number and characteristics of these cells may accompany anemia, infectious, inflammatory, oncological, hematological, and other diseases.
The service includes two tests: an automated CBC with a white blood cell differential and ESR. During the CBC, the number and characteristics of blood cells and the proportions of different types of white blood cells are determined automatically. ESR is a parameter that may change in inflammation and a number of other conditions. This comprehensive blood test makes it possible to assess several groups of parameters simultaneously, but for diagnostic purposes, the results are interpreted together with symptoms, health status, and the results of other examinations.
Complete blood count parameters
The results of a complete blood count include a number of interrelated parameters. Some are measured directly during the test, while others are calculated based on the values obtained. Together, they characterize the number, size, and other characteristics of red blood cells, white blood cells, and platelets. ESR is also determined as part of the service. For convenience, the parameters can be divided into several groups.
Red blood cell parameters
Red blood cells (RBCs) are red blood cells that carry oxygen from the lungs to the tissues and some of the carbon dioxide in the opposite direction. Red blood cell parameters provide information about the number of these cells, hemoglobin level, their average size, and differences between them. Together, these data help identify signs of anemia and other changes in red blood cells.
This group includes:
- red blood cells (RBC) – the number of red blood cells;
- hemoglobin (HGB) – a protein in red blood cells that carries oxygen;
- hematocrit (HCT) – the proportion of blood volume occupied by red blood cells;
- mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) – calculated indices that characterize the size of red blood cells and their hemoglobin content;
- red cell distribution width (RDW-CV and RDW-SD) – parameters reflecting differences in red blood cell size.
White blood cells and white blood cell differential
White blood cells (WBCs) are cells of the immune system involved in protecting the body. As part of the test, their total number is determined, as well as the percentage and absolute counts of different types of white blood cells:
- neutrophils, which are involved in protection against infections, particularly bacterial infections;
- lymphocytes, which are involved in recognizing pathogens, producing antibodies, destroying infected cells, and forming immune memory;
- monocytes, which engulf microorganisms and damaged cells;
- eosinophils, which are involved, among other things, in allergic reactions and protection against parasites;
- basophils, which are involved in inflammatory and allergic reactions;
- immature granulocytes – young forms of cells, the number of which may change in response to infection, inflammation, or other conditions.
Changes in the total white blood cell count or white blood cell differential may be observed in infectious, inflammatory, allergic, autoimmune, hematological, and other diseases. At the same time, the cause of the changes cannot be determined based on an individual parameter alone.
Platelet parameters
Platelets are small cellular components of the blood that help form a blood clot and stop bleeding after a blood vessel is damaged. As part of a CBC, their number, average size, differences between them, and proportion of total blood volume are assessed.
Platelet parameters include:
- platelets (PLT) – their number in the blood;
- mean platelet volume (MPV);
- platelet distribution width (PDW);
- plateletcrit (PCT) – the proportion of blood volume occupied by platelets.
A decrease in the platelet count may be accompanied by a tendency to develop bruises or bleeding. At the same time, a CBC does not assess all components of the blood coagulation system, so the results are interpreted together with other parameters and information about the individual’s health status.
Erythrocyte sedimentation rate
ESR (erythrocyte sedimentation rate) shows how quickly red blood cells settle in a blood sample. The parameter may increase in infectious, inflammatory, autoimmune, and other diseases, and may also change under the influence of age, anemia, and other factors. ESR does not indicate a specific cause of inflammation, so it is interpreted together with other results and symptoms.
A complete blood count with a white blood cell differential and ESR is a basic test, but its results do not replace a physician’s evaluation or other examinations necessary to establish a diagnosis.
CBC: reference ranges
For each CBC parameter, the laboratory provides reference values on the report – a range against which the obtained result is compared. These ranges may depend on age, sex, testing method, and laboratory equipment, so the ranges provided on the report should be used when interpreting the results.
An abnormal result for one or more parameters does not always indicate the presence of a disease, just as a result within the reference range does not always rule out a disorder. The parameters are interpreted comprehensively, taking into account symptoms, health status, and the results of other examinations.
