Description
Differential blood count can be performed by the following 2 methods:
Automated differential blood count: Automated hematology instruments using multiple parameters and methods (such as fluorescence flow cytometry and impedance) are used to count and identify the 5 major white blood cell types in blood (so-called 5-part differential count): neutrophils, lymphocytes, monocytes, eosinophils and basophils. [4, 5]
Manual differential blood count: This is performed by visual examination of peripheral blood smear (blood films) by trained personnel. [4]
The automated differential blood count is less time-consuming and less expensive than routine examination of blood smear. With the automated technique, thousands of white blood cells can be examined, whereas typically 100-200 white blood cells are examined by visual examination. [6]
Indications/Applications
Differential blood count is primarily needed in the 2 following reasons. [2]
To look for quantitative abnormalities in morphologically normal WBC population such as in the diagnosis of infectious or allergic diseases and for therapeutic monitoring of cytotoxic or myelotoxic drugs (This requires a high level of precision and accuracy [ie, ability to provide consistent and correct results]).
To look for morphologic abnormalities of white blood cells (eg, when circulating abnormal white blood cell population such as immature or atypical cells are suspected for diagnostic or monitoring reasons; this requires a high level of clinical sensitivity, [ie, ability to identify all patients who have circulating abnormal WBCs]).
Considerations
Accuracy, precision, and clinical sensitivity
The automated differential blood count provides a high level of accuracy and precision (correct and consistent results) for quantification and identification of normal white blood cells; however, this method is not sensitive at identifying abnormal or immature cells and is not able to accurately identifying and classifying all types of white blood cells. To overcome this problem, most automated analyzers will flag samples with possible abnormal white blood cell populations, indicating the need for peripheral smear examination to be examined by trained personnels to identify abnormal cells. [6, 2]
Monocyte count and basophil count are the most difficult population to count and have a low level of precision and accuracy. Moreover, automated analyzers tend to underestimate the basophil count during true basophilia. [2]
False negative
Both automated and manual methods may not detect small numbers of abnormal cells. The false negative rate for detection of abnormal cells varies from 1-20%, depending on the instrument and the detection limit desired (1-5% abnormal cells). The most difficult for both automated instruments and visual examination by human is identification of lymphoma cells and reactive lymphocytes. [5]
Band neutrophils and immature granulocytes (IGs)
The value of reporting band neutrophils is questionable. The measurement of the immature cells of the myeloid lineages, specifically “band,” has been considered clinically useful in the diagnosis of infections, especially neonatal sepsis. [7]
However, band neutrophils cannot be enumerated by automated analyzers and are reported together with segmented neutrophils as absolute neutrophil counts (ANC), which are used to defined neutropenia or neutrophilia. Identification of band neutrophils by visual examination (manual differential blood count) is neither precise nor consistent, as a high variability of morphologic classification or quantification of band neutrophils exists due to interobserver variability.
Some, therefore, advocated ceasing quantitative reporting of band neutrophils. [5, 2] The extended differential count includes reporting immature granulocytes (IG) can be used alternatively to help diagnosis neonatal sepsis. [2] For further reading, see Interpretation.
— Written By Marijke Vroomen Durning, RN
Updated on January 5, 2022
What are lymphocytes?
Lymphocytes are a type of white blood cell, which are part of the body’s immune system. There are three types of lymphocytes and they make up from 20 to 40% of the total blood volume. Blood tests indicate how many lymphocytes are circulating through the body.
Too many lymphocytes in the blood is called lymphocytosis. The most common cause of excessive lymphocytes is an infection, but lymphocyte levels can also rise if there are other conditions, such as leukemia.
Too few lymphocytes is called lymphocytopenia or lymphopenia. Although a viral infection can cause it, other factors, such as fasting or severe physical stress can reduce lymphocyte numbers as well.
Lymphocytes develop in the bone marrow, the soft spongy tissue inside bones, and in the thymus. The thymus is a small organ behind the breast bone, just above the heart.
Treatment for high or low levels of lymphocytes in the blood depends on the cause. Promptly treating infections will help prevent serious complications. Treatment of lymphoma and other types of cancer in the early stages is often successful.
If a blood test shows your lymphocyte level is out of the normal range, your healthcare professional will discuss next steps with you, which may include additional tests to determine an underlying cause and, if necessary, guide treatment.
What are the different types of lymphocytes?
There are three types of lymphocytes. The two main types are B cells and T cells. The third is the NK, or natural killer cell. This is a brief explanation of their function:
B cell lymphocytes are produced in the bone marrow. They make antibodies against foreign antigens like bacteria.
T cell lymphocytes are either helper cells or killer cells. The helper T cells help the B cells make antibodies. Killer T cells directly kill antigens, usually viruses. T cells may also kill cancer cells.
- NK cells kill antigens, particular cancer cells.
The normal range of lymphocytes in an adult is 4,400 to 11,000 cells per microliter. Less than that is lymphocytopenia or lymphopenia. More than that might indicate lymphocytosis.
What are the symptoms of low or high levels of lymphocytes?
There are several potential causes for lymphopenia and lymphocytosis.
Symptoms of lymphopenia
The most common symptoms of lymphopenia/lymphocytopenia are:
Enlarged lymph nodes, usually noticeable in the neck and groin
Enlarged spleen, which the doctor or nurse practitioner can feel during a physical exam
Rash
Signs of a viral infection, such as fever, but specific symptoms depend on the type of infection
- Sore joints
Symptoms of lymphocytosis
Lymphocytosis does not usually cause symptoms. Medical professionals most often discover it during blood tests for a routine doctor’s appointment or a diagnostic work up for another condition.
What causes low or high lymphocytes?
There are several potential causes for lymphopenia and lymphocytosis.
Common causes of lymphopenia
The most common causes of lymphopenia/lymphocytopenia are:
Medications like chemotherapy, which suppress the immune system
Aplastic anemia
Autoimmune disorders such as lupus
Cancers such as Hodgkin lymphoma
AIDS
COVID-19
Viral hepatitis
Tuberculosis
- Severe illnesses and traumas
Common causes of lymphocytosis
The most common lymphocytosis causes are:
Leukemia and lymphoma
Viral infections like mononucleosis, measles, chickenpox, and viral pneumonia, among others
Drug reactions
Some bacterial diseases, such as tuberculosis and whooping cough (pertussis)
Addison’s disease
- Surgical removal of the spleen
How do doctors diagnose the cause of low or high levels of lymphocytes?
Once a blood test reveals an abnormal number of lymphocytes in the blood, the doctor needs to do more investigations to determine why.
Your doctor might ask questions like:
Have you been sick or exposed to any contagious illnesses recently?
What symptoms are you experiencing, if any?
- How long have you had these symptoms?
Tests will depend on what the doctor suspects. You may need more blood tests as well as imaging (X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) and ultrasounds).
Other tests could include swabs of discharge and biopsies.
What are the treatments for low or high lymphocyte counts?
Treating lymphocyte abnormalities depends on the cause. For example, medical professionals treat infections with antimicrobials and cancers with chemotherapy, radiation therapy, surgery, or targeted therapies. Lymphocyte counts should return to the normal range after treatment.
Sometimes, treatment is as simple as discontinuing a medication that is causing lymphocytopenia. Other times, treatment is lifelong, especially if the cause is a chronic illness like lupus.
If the lymphocyte count is too low, doctors may administer gamma globulin, by intravenous (IV), to help boost the body’s immunity against disease. Gamma globulin contains antibodies. This will help reduce the risk of infections.
What are the potential complications of low or high lymphocyte counts?
Since lymphocytes are part of the immune system, too few in the blood system means that there is a higher-than-average risk of infection. In cases of lymphocytosis, an excess number of circulating lymphocytes could lead to rupture of the spleen, reduced levels of gamma globulin to fight infection, and leukostasis (sluggish blood flow), which could cause stroke, myocardial infarction, and loss of vision.