Absolute lymphocyte count (ALC) has become an important prognostic tool in the management of many diseases. ALC in disease conditions could yield lymphocytopenia or lymphocytosis. The two have different meanings which we shall discuss later. Â
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Methods of Obtaining Absolute Lymphocyte Count
Absolute lymphocyte count means the absolute number of lymphocytes and not a percentage of the same. There are two important tests that we can use in the laboratory to obtain this data. Let’s briefly discuss them here:
Full Hemogram or Complete Blood Count
Complete blood count test (CBC) is a very common test and indeed a starting point in most cases before other tests can be ordered. You need to note that CBC enumerates all blood cells including the red blood cells and platelets.
Lymphocytes normally account for 20 to 40% of all white blood cells in your body. To calculate ALC you need to multiply the percentage of lymphocytes by the total number of your white blood cells.
Once you obtain this number, you need to interpret it against the documented reference values. The outcome could be low, normal, or high.
Flow Cytometry
In immunology, flow cytometry delivers a solution for nearly all problems. We only need to have reagents (Fluorochrome-labelled monoclonal antibodies). Monoclonal antibodies are special proteins of a single specificity that can help us be able to count your lymphocytes from the blood sample.
The lymphocyte markers that are bound by monoclonal antibodies to help us count your lymphocytes include cell surface proteins like CD4, CD8, CD3, CD20, CD19, and CD25 among others depending on the type of lymphocytes.
The laboratory technologists/technicians know which ones to target to be able to count your lymphocytes accurately. You don’t have to worry about accuracy because they have been trained to do this.
High Absolute Lymphocyte Count (Lymphocytosis)
The normal range of lymphocyte count in your blood as an adult is 1000 to 4800 cells/µL. The range for children is higher at 3,000 and 9,500 cells/µL. These ranges may be reported slightly differently in various laboratories, but the difference should be insignificant.
Lymphocytosis is defined as when your ALC is above the upper limit of the range. It is quite common when you have an infection. ALC will not be sufficient to make a diagnosis.
However, it will give a direction on what next set of tests should be conducted. Your doctor will order the same to ensure that your health problem is well determined and treated.
One reason you may have lymphocytosis is a viral infection. Your body responds by increasing the number of lymphocytes to contain the infection. Other diseases that can make you have lymphocytosis include:
- HIV and AIDS
- Acute Hepatitis
- Cytomegalovirus
- Lymphoma and leukemia
- Acute Syphilis
- Mononucleosis
- Toxoplasmosis
- Tuberculosis
- Hypothyroidism
Symptoms of Lymphocytosis
For you to seek medical attention for a possible Absolute lymphocyte count test, there are symptoms that you can look out for. Some of these include swelling of the tonsils, enlargement of lymph nodes, and insomnia among others. Look at the diagram below to see some more:
Low Absolute Lymphocyte Count (Lymphocytopenia)
Lymphocytopenia is defined as when your ALC is below 1000 cells/µL. You will mostly have lymphocytopenia when you have a common cold. However, there are many other reasons for lymphocytopenia as you can see in the diagram below.
The following is a list of some of the conditions that have also been associated with lymphocytopenia:
- Primary immunodeficiency diseases like Wiskott-Aldrich syndrome, SCID, and DiGeorge syndrome
- HIV/AIDs
- Autoimmune diseases like systemic lupus erythematosus.
- typhoid fever
- After radiotherapeutic cancer treatment
- Viral hepatitis
- After chemotherapeutic cancer treatment
Absolute Lymphocyte Count In COVID-19
Absolute lymphocyte count (ALC) has become an important prognostic tool for the management of COVID-19. Lymphocytopenia which is defined as an ALC of less than 1000 cells/µL has frequently emerged helpful as it correlates with poor COVID-19 outcomes. Research is still ongoing to ascertain this correlation reliably.
Types of Cells Counted in Absolute Lymphocyte Count
There are two broad categories of lymphocytes in your body. These are the B lymphocytes also called B cells and the T lymphocytes also called T cells. These categories are further subdivided. We shall give some details of each of the types of lymphocytes here:
B Cells
These are very important cells in your blood. They are produced in your bone marrow. They are the only cells that are capable of producing antibodies. The B cells have receptors called B cell receptors (BCRs) that they use to recognize foreign bodies.
Examples of foreign bodies they can recognize include viruses, bacteria, protozoa, fungi, tumor cells, and many others. The B cells then become specialized cells called plasma cells that produce specific antibodies against the recognized antigens.
Some of them become memory B cells respond readily to microorganisms the next time you are attacked by the same antigens.
T Helper Cells
These are arguably the most important cells in your body. These cells are produced in the bone marrow but migrate for maturation in your thymus. When they encounter an antigen they then produce proteins called cytokines that help activate other cells like your B cells to produce antibodies. They recognize foreign bodies using their T cell receptors (TCRs). They also possess cell surface markers called CD4 which distinguishes them from the B cells.
Cytotoxic T cells
These cells are distinguished from T helper cells by the CD8 marker that they have on their surface. The cytotoxic cells are named so because they possess toxic granules (Granzymes and perforins) in their cytoplasm that they use to kill infected cells. They particularly target virally infected cells.
T Regulatory Cells
The T regulatory cells possess the same CD4 as their T helper cells colleagues. However, they have other markers like CD25 and FOXP3 that distinguishes them from T helper cells.
T regulatory cells are important in ensuring that your immune response does not go overboard. They are like the brakes of a vehicle that slow the vehicle down. They ensure that your immune system that does not revert to attacking your own cells once it’s done with microorganisms.
Natural Killer (NK) cells
When lymphocytes are being discussed, these cells are sometimes forgotten. They are loosely referred to as ‘lymphocytes of the innate immune system‘. They use special receptors to recognize and bind to antigens and not the T cell receptors (TCRs) like the other lymphocytes.
An important similarity between them and the CD8+ cytotoxic T cells is that they also contain cytotoxic granules i.e granzymes and perforins which they use to kill their targets. Their targets are virally-infected cells and tumor cells among others.
Conclusion
Absolute lymphocyte count (ALC) is an important diagnostic tool in the management of many disease conditions. ALC is not a confirmatory diagnosis for any disease but provides guidance on the direction the diagnosis should take. It has also served as a prognostic tool for diseases including COVID-19. In the case of COVID-19, lymphocytopenia at the initial stages of the disease is thought to be a predictor of poor prognosis.
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