What is the significance of the total number and classification of white blood cells in routine blood tests as an important reference for clinicians in diagnosing and treating diseases?
The total number and classification of white blood cells in routine blood tests is an important reference for clinicians in the diagnosis and treatment of diseases, especially in the diagnosis and treatment of acute fever and infectious diseases in pediatrics, where routine blood tests are often essential to distinguish bacterial or viral infections and the severity of infection. However, in my daily work, I often find that some parents or physicians’ one-sided analysis of total leukocyte count and classification leads to the misuse of antibiotics or bias in the judgment of disease severity. Here, I would like to discuss briefly and offer my own opinion.
The total leukocyte count and classification values (both absolute and relative percentages) are indicators of inflammation; in other words, both infectious and non-infectious inflammation can cause changes in these parameters.
In pediatric children with fever, leukocyte and categorical values often reflect infectious inflammation and are often used as indicators to identify bacterial or non-bacterial infections. That is, bacterial infections are often manifested by elevated absolute values and percentages of total white blood cells and neutrophils. However, in complex chronic, recurrent episodes of disease (e.g. asthma, allergic cough, allergic enteropathy, etc.) and severe infections accompanied by a systemic inflammatory response (e.g. severe infections caused by various pathogens, infectious shock), the above values must be judged with caution because it is affected by both infectious and non-infectious inflammation.
● The leukocytes are usually normal or decreased in viral infections, and the percentage of lymphocytes in the classification is increased, but the total leukocyte count and neutrophils can be increased in some specific viruses or viral infection syndrome.
● Total leukocyte count and classification, as one of the 3 important pieces of information in blood routine (the other 2 are red blood cell and platelet count), are also important indicators of blood disorders and bone marrow function. For example, leukemia, leukopenia, etc.
Common misconceptions about the total number and classification of white blood cells in routine blood tests Misconception 1 The normal values of the total number and classification of white blood cells in adults are used to judge the laboratory values in children.
The total number of leukocytes (see Table 1) and the classification of leukocytes in routine blood tests vary greatly by age group in children. Leukocytes are mainly divided into granulocytes (including neutrophils, eosinophils and basophils) and lymphocytes (monocytes). The changes in the classification of leukocytes were more prominent in granulocytes and lymphocytes: lymphocytes were predominant between 4-6 d and 4-6 years of age, accounting for about 60% of the total; neutrophils were about 30%. In contrast, neutrophils predominate between 4-6 d after birth and after 4-6 years of age until adulthood, accounting for about 65%.
The normal range of leukocyte values varies in different textbooks at home and abroad, but the trend is the same for all age groups. This is a big misconception and an important reason for the misuse of antibiotics.
This is a big misconception, and is also an important cause of antibiotic abuse. Myth 2: High total leukocyte count and classification values are used as indicators of untreated infectious diseases and as evidence for continued use of antibiotics.
In fact, in children with cough without fever and no obvious infectious lesions, a mild increase in WBCs is not very meaningful and cannot distinguish between bacterial or viral infections. This is because there are several factors that can cause an increase in the total number of leukocytes in blood tests, such as stress, crying, sports or activity, vaccinations, painful irritation, etc. Different times of the day, medications, food, etc. can also change the white blood cell values. It has been observed that the white blood cell count in routine blood can drop from (15.0-20.0) × 109/L to 10.0 × 109/L (i.e., from 15,000-20,000 per cubic millimeter to less than 10,000) within 12 to 24 h without any intervention.
Myth 3 Over-interpretation of total leukocyte count and classification, such as mechanical and simple use as an indicator to determine the pathogen of infection and antibiotic selection.
Analysis The process of diagnosis and treatment of diseases is based on the comprehensive information of medical history, signs and laboratory tests, and the analysis of the etiology and pathogenesis followed by the treatment for the etiology or pathophysiological mechanism, while there is a current practice of using the total white blood cell count and classification solely as the etiology and pathogenesis for diagnostic analysis, or even as evidence of the etiology and pathophysiological mechanism (including anti-infective and anti-inflammatory treatment), while ignoring the overall patient symptoms Phenomenon of ignoring the patient’s overall symptoms and other laboratory test data.
Knowledge of the process of leukocyte production, circulation and clearance is helpful to correct misconceptions As already mentioned above, leukocytes are mainly composed of granulocytes and lymphocytes. The granulocytes are derived from bone marrow hematopoietic stem cells, and most of them remain in the bone marrow storage pool for 3 to 5 d. Granulocytes released into the peripheral blood enter the blood circulation and become the peripheral blood functional pool. About half of the granulocytes in the peripheral functional pool run with the blood circulation, that is, they enter the circulating pool, and the other half are attached to the walls of small veins or capillaries without entering the circulation, which is called the marginal pool. The leukocyte count in the routine blood count of peripheral blood only reflects the granulocyte value in the circulating pool. The granulocytes in the circulating pool and the marginal pool are often exchanged randomly and are in dynamic equilibrium. Neutrophils remain in the circulation for about 10-12 h with a half-life of 6-7 h, averaging 6.3 h. They then escape in a random manner from the walls of the blood vessels in capillary-rich organs, such as the lungs, digestive tract, and spleen, into the tissues (called the tissue granulocyte pool). In contrast, the granulocytes in the tissues are about 20 times larger than those in the blood vessels. The granulocytes that enter the tissues no longer return to the circulation, but exert anti-microbial effects such as adhesion, phagocytosis and bactericidal effects, survive for 1 to 3 d before senescence and death, and then are removed by the body’s monocyte-macrophages, and a few are excreted through saliva, sputum, digestive fluid or the genitourinary tract.
Conclusion: (1) routine leukocyte count in peripheral blood reflects only a small fraction of the total number of leukocytes in the body; (2) leukocytes are in a more rapid dynamic equilibrium process; (3) factors affecting the leukocyte count include the amount of leukocytes released from the bone marrow storage pool, the amount of marginal pool leukocytes entering the circulating pool, and the amount of leukocytes escaping from the blood vessels to extravascular tissues.
In summary when complex recurrent conditions occur, it is not advisable to judge disease and decide on antibiotic application based on peripheral blood leukocyte values alone, or to be afraid to stop antibiotics or even to stop infusions simply because of high leukocytes (e.g., 10.0 × 109/L).
Due to complex factors, total leukocyte count and classification values require comprehensive analysis and judgment by physicians, such as a perfect medical history and physical examination, and accurate judgment can obtain clues to the mechanism of disease occurrence and early detection of problems; while overly simple interpretation of blood routine can lead to misjudgment of disease and drug abuse. It can even be said that physicians’ judgment of blood routine results is a matter of opinion.