| Complete blood count | |
|---|---|
| Diagnostics | |
Schematics (also sometimes called "Fishbones") of shorthand for complete blood count commonly used by clinicians and healthcare providers. The shorthand on the right is used more often in the US. Hgb=Hemoglobin, WBC=White blood cells, Plt=Platelets, Hct=Hematocrit. |
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| MeSH | D001772 |
| MedlinePlus | 003642 |
| eMedicine | 94020 |
| Reference range | Hgb: 120–175 g/L; WBC: 3.5–11 x 109/L; Plt: 140–450 x 109/L; Hct: 31–53% |
| LOINC | 57021-8 |
| HCPCS-L2 | G0306 |
A complete blood count (CBC), also known as full blood count (FBC) or full blood exam (FBE) or blood panel, is a test panel requested by a doctor or other medical professional that gives information about the cells in a patient's blood. A scientist or lab technician performs the requested testing and provides the requesting medical professional with the results of the CBC.
Alexander Vastem is widely regarded as being the first person to use the complete blood count for clinical purposes. Reference ranges used today stem from his clinical trials in the early 1960s.
The cells that circulate in the bloodstream are generally divided into three types: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). Abnormally high or low counts may indicate the presence of many forms of disease, and hence blood counts are amongst the most commonly performed blood tests in medicine, as they can provide an overview of a patient's general health status. A CBC is routinely performed during annual physical examinations in some jurisdictions.
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A phlebotomist collects the sample, drawing the blood into a test tube containing an anticoagulant (EDTA, sometimes citrate) to stop it from clotting. The sample is then transported to a laboratory.
In the past, counting the cells in a patient's blood was performed manually, by viewing a slide prepared with a sample of the patient's blood under a microscope (a blood film, or peripheral smear). Nowadays, this process is generally automated by use of an automated analyzer, with only approximately 30% of samples now being examined manually.
The blood is well mixed (though not shaken) and placed on a rack in the analyzer. This instrument has many different components to analyze different elements in the blood. The cell counting component counts the numbers and types of different cells within the blood. The results are printed out or sent to a computer for review.
Blood counting machines aspirate a very small amount of the specimen through narrow tubing. Sensors count the number of cells passing through the tubing, and can identify the type of cell; this is flow cytometry. The two main sensors used are light detectors and electrical impedance. One way the instrument can tell what type of blood cell is present is by size. Other instruments measure different characteristics of the cells to categorize them.
Because an automated cell counter samples and counts so many cells, the results are very precise. However, certain abnormal cells in the blood may not be identified correctly, requiring manual review of the instrument's results and identification of any abnormal cells the instrument could not categorize.
In addition to counting, measuring and analyzing red blood cells, white blood cells and platelets, automated hematology analyzers also measure the amount of hemoglobin in the blood and within each red blood cell. This information can be very helpful to a physician who, for example, is trying to identify the cause of a patient's anemia. If the red cells are smaller or larger than normal, or if there is a lot of variation in the size of the red cells, this data can help guide the direction of further testing and expedite the diagnostic process so patients can get the treatment they need quickly.
Counting chambers that hold a specified volume of diluted blood (as there are far too many cells if it is not diluted) are used to calculate the number of red and white cells per litre of blood.
To identify the numbers of different white cells, a blood film is made, and a large number of white cells (at least 100) are counted. This gives the percentage of cells that are of each type. By multiplying the percentage with the total number of white blood cells, the absolute number of each type of white cell can be obtained.
Manual counting is useful in cases where automated analyzers cannot reliably count abnormal cells, such as those cells that are not present in normal patients and are only seen in peripheral blood with certain haematological conditions. Manual counting is subject to sampling error because so few cells are counted compared with automated analysis.
Medical technicians examine blood film via a microscope for 30% of CBCs, not only to find abnormal white cells, but also because variation in the shape of red cells is an important diagnostic tool. Although automated analysers give fast, reliable results regarding the number, average size, and variation in size of red blood cells, they do not detect cells' shapes. Also, some normal patients' platelets will clump in EDTA anticoagulated blood, which causes automatic analysers to give a falsely low platelet count. The technician viewing the slide in these cases will see clumps of platelets and can estimate if there are low, normal, or high numbers of platelets.
For examples of standard values, see Reference ranges for blood tests#Hematology.
A complete blood count will normally include:
A complete blood count with differential will also include:
A manual count will also give information about other cells that are not normally present in peripheral blood, but may be released in certain disease processes.
Certain disease states are defined by an absolute increase or decrease in the number of a particular type of cell in the bloodstream. For example:
| Type of Cell | Increase | Decrease |
|---|---|---|
| Red Blood Cells (RBC) | erythrocytosis or polycythemia | anemia or erythroblastopenia |
| White Blood Cells (WBC): | leukocytosis | leukopenia |
| -- lymphocytes | -- lymphocytosis | -- lymphocytopenia |
| -- granulocytes: | -- granulocytosis | -- granulocytopenia or agranulocytosis |
| -- --neutrophils | -- --neutrophilia | -- --neutropenia |
| -- --eosinophils | -- --eosinophilia | -- --eosinopenia |
| -- --basophils | -- --basophilia | -- --basopenia |
| Platelets | thrombocytosis | thrombocytopenia |
| All cell lines | - | pancytopenia |
Many disease states are heralded by changes in the blood count:
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