Generality
The leukocyte formula is a blood test that quantifies the number of white blood cells in a cubic millimeter of blood, also expressing the quantitative and percentage ratio of the various types of white blood cells .
Five types are known (neutrophils, eosinophils, basophils, lymphocytes, monocytes), each of which has some specific functions and a relatively stable percentage ratio from individual to individual.
Exactly quantifying the white blood cell subpopulation using the leukocyte formula helps doctors assess the patient's health status and make a diagnosis.
Also known as a leukocyte differential count, the leukocyte formula is performed on a sample of blood taken from the patient, which must be in basal conditions after a fast of about 10 hours. Important physical stresses and stresses before the exam can alter the values.
The leukocyte formula is normally inserted into the blood count, a "standard" blood test that also includes the counts of red blood cells and platelets, as well as additional and important blood parameters.
The count can be made automatically by electronic meters, or by observation of a drop of blood streaked on a glass slide (see blood smear).
What's this
The leukocyte formula consists of counting and morphological analysis of each type of white blood cell . This examination is of fundamental importance, since it provides an extremely precise perspective of what is the composition - in terms of number and quality - of these cells within our body.
Why do you measure
The leukocyte formula is a test used to determine the composition of white blood cells within our blood. This analysis is able to offer an observation of fundamental importance for the diagnosis of some pathological conditions, since it allows to understand precisely if the number of white blood cells is high or reduced.
The differential leukocyte count includes:
- Count or% of neutrophils;
- Count or% of lymphocytes;
- Count or% of monocytes;
- Count or% of eosinophils;
- Count or% of basophils.
When is the leukocyte formula examined?
The leukocyte formula is performed as a support in making the diagnosis of a specific cause of pathology, when the doctor suspects for example:
- Infections caused by bacteria, viruses, fungi or parasites;
- Inflammation;
- Allergies;
- Asthma;
- Immune disorders (acquired or non-acquired immunodeficiencies, autoimmune diseases, etc.);
- Leukemia;
- Myelodysplastic syndrome;
- Myeloproliferative neoplasms.
Normal values
The table shows the reference values for the leukocyte formula, remembering that the normal ranges may vary slightly depending on the laboratory that carries out the analysis and on the type of reference population (sex, age, etc.); the parameters reported in the report of the analysis center are therefore authentic.
NEUTROPHILSTheir main task is the defense of the organism against infections, especially if caused by bacteria. They contain different proteins and chemical substances, capable of irreversibly damaging the membranes of pathogenic microorganisms | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 40-75% | 2, 000 - 8, 000 / mmc |
LYMPHOCYTESIn reality lymphocytes include different subtypes: the main ones are the B, T and Natural Killer lymphocytes. These subpopulations have different functions: ilinfociti B produce antibodies, important molecules in the defense of the organism against infections; T lymphocytes do not produce antibodies but produce other important molecules in defense against infections, especially viral ones. They are also able to specifically recognize foreign cells and play an essential role in defending the body from tumors and in transplant rejection. Natural Killer (NK) cells are similar to T lymphocytes. | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 25-55% | 1, 500 - 5, 000 / mmc |
MONOCYTES OR MACROPHAGESThey are important in defending the body from certain types of bacteria, such as the one that causes tuberculosis. Phagocyte and digest foreign elements and damaged cells. | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 2-10% | 100 - 900 / mmc |
EOSINOPHILSTheir main function is the defense of the organism from some types of parasites. Eosinophils also increase in allergic diseases (bronchial asthma, allergic rhinitis, urticaria etc.) and may be responsible for some of the characteristic symptoms of these diseases. | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 0.5-6% | 20 - 600 / mmc |
BASOPHILSTheir function is not very well known. They also increase in allergies: they contain histamine which, if released in excess in the blood and tissues, causes annoying symptoms (such as itching or the appearance of cutaneous wheals), to combat which drugs often called antihistamines are often used. | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 0-2% | 2 - 150 / mmc |
TOTAL NUMBER OF LEUCOCYTES | |
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE |
| 100% | 4, 000 - 10, 500 / mmc |
- in green the group of granulocytes (neutrophils, basophils and eosinophils)
NOTE: between the two values (percentage and absolute) it is more important to consider the absolute one; in fact, evaluating the only percentage value is likely to misinterpret the outcome of the leukocyte count. For example, the latter could be excessive or too low even when it is absolutely normal in absolute terms; this can happen for the simultaneous increase or reduction of another category of leukocytes, with variation of the absolute number of white blood cells.
In some reports the absolute values of the leukocyte types can be indicated with different units of measurement; it is therefore necessary to carry out the necessary conversions to return to the measurement units shown in the table. The abbreviation x10E3 (or x10 ** 3) means that the corresponding value must be multiplied by 1000; the letters mmc mm3 and µl are equivalent.
| PERCENTAGE NORMAL VALUES | ABSOLUTE VALUES FOR MILLIMETER CUBE | |
| NEUTROPHILS | 40-75% | 2, 000 - 8, 000 / mmc = 2-8x10E3 |
| LYMPHOCYTES | 25-55% | 1, 500 - 5, 000 / mmc = 1.5-5x10E3 |
| MONOCYTES OR MACROPHAGES | 2-10% | 100 - 900 / mmc = 0.1-0.9x10E3 |
| EOSINOPHILS | 0.5-6% | 20 - 600 / mmc = 0.02-0.6x10E3 |
| BASOPHILS | 0-2% | 2 - 150 / mmc = 0, 0-0, 15x10E3 |
High and Low leukocyte formula - Causes
NEUTROPHILS | |
| CAUSES HIGH VALUES = Neutrophilia | CAUSES LOW VALUES = Neutropenia |
Acute infections (bacterial and fungal) Acute stress Eclampsia Gout Myeloid leukemias Rheumatoid arthritis Rheumatic fever traumas tumors Sterile inflammatory diseases / tissue necrosis (Burns, myocardial infarction) thyroiditis Anxiety and severe physical activity Collagen diseases Acute renal failure ketoacidosis splenectomy | Congenital neutropenia Lymphomas Bone marrow diseases Serious infections Aplastic anemia Flu or other viral infections Anaphylactic shock Taking some medicines (eg methotrexate) and chemotherapy Radiation therapy or exposure to ionizing radiation |
LYMPHOCYTES | |
| CAUSES HIGH VALUES = Lymphocytosis | CAUSES LOW VALUES = Lymphocytopenia |
Lymphatic leukemias Chronic bacterial infections Infectious mononucleosis and other viral diseases (mumps, measles, flu, chickenpox, herpes simplex, viral hepatitis) Rheumatic diseases Multiple myeloma Drug addiction Inflammation | Congenital deficiencies AIDS (terminal stages) and diseases of the immune system (lupus) Severe renal failure with uremia Chemotherapy Radiation therapy or exposure to ionizing radiation Chronic diseases (sarcoidosis, lupus, multiple sclerosis, myasthenia gravis, Guillain Barré syndrome) |
MONOCYTES OR MACROPHAGES | |
| CAUSES HIGH VALUES = Monocytosis | CAUSES LOW VALUES = Monocytopenia |
Leukemia Myeloma Infectious mononucleosis Liver cirrhosis Chronic inflammatory diseases Tuberculosis, syphilis, brucellosis, listeriosis Chronic infections Bacterial endocarditis | Leukemia Myeloma Chemotherapy and immunosuppressive treatments Aplastic anemia |
EOSINOPHILS | |
| CAUSES HIGH VALUES = Eosinophilia | CAUSES LOW VALUES = Eosinophilopenia |
| Allergies (bronchial asthma, allergic rhinitis, urticaria etc.) Hypersensitivity to drugs Autoimmune diseases Parasitic diseases Scarlet fever | Hypoglycemia Prolonged exposure to sunlight Shock Stress (also due to trauma and surgery) Chronic renal failure Use of corticosteroids Cushing syndrome |
BASOPHILS | |
| CAUSES HIGH VALUES = Basophilia | CAUSES LOW VALUES = Basophilopenia |
| Some types of Leukemia gangrene Chronic infections Allergic reactions to food (IgE mediated) parasitosis Following radiotherapy | Pregnancy Hyperthyroidism Acute stress and hypercortisolism Often associated with eosinophilopenia |
Also some drugs can alter the values of the leukocyte formula.
Prolonged use of steroids and long-term exposure to toxic elements (such as caustic soda or insecticides) may increase the risk of having an abnormal result in the differential white blood cell count.
How to measure it
For the leukocyte formula, it is enough to undergo a complete blood count (blood count), where we will also proceed to the analysis of red blood cell and platelet counts, to the calculation of hematocrit and corpuscular indexes. A sample of blood from a vein in the arm, usually in the morning and fasting, is then taken from the patient.
Counting can be done automatically by electronic meters or by observation with an optical microscope (blood smear).
Online converter
In the previous chapter we have seen that to assess whether there is a real increase (or decrease) in a leukocyte type it is necessary to consider not so much the relative percentage, but the absolute value of that leukocyte subpopulation. If this last datum is not included in the report, it is however possible to calculate it starting from the total number of leukocytes and the relative percentage of the five types of white blood cells:
just multiply the percentage of the type of leukocyte considered by the total number of white blood cells and divide the result by 100, or simply assign the calculation to this automatic converter.
Preparation
To undergo blood sampling useful for the evaluation of the leukocyte formula, it is necessary to abstain from food and drink for at least 8-10 hours. The general practitioner who prescribes the analyzes will still be able to provide useful information for the case.
Interpretation of Results
- The result of the leukocyte formula indicates the number and / or percentage of each type of white blood cell present in the patient's blood. In making the diagnosis, the doctor will consider the degree of increase or decrease of the cells, as well as assess the symptoms and the clinical history of the individual.
- Often, numbers are reported in absolute value of the five types of leukocytes and / or as percentages of the total white blood cell count. Absolute values are calculated by multiplying the total number of leukocytes by the percentage of all types of white blood cells. This information can provide a specific pathology diagnosis and therapy monitoring.
- When the report is read, attention must also be paid to the interpretation of the differential count result . Sometimes, this last datum allows to detect, in fact, some immature and / or abnormal cellular forms present in the blood. Immature forms include metamyelocytes, myelocytes, promyelocytes and / or blasts. When this occurs, further tests may be indicated (eg bone marrow biopsy).
- Some factors can cause transient increases or decreases in the number of each cell type. A persistent high or low leukocyte formula requires further testing to determine its exact cause.
