Leukocyte Differential Count

LEUKOCYTE DIFFERENTIAL COUNT OF THE BLOOD, the percentage relationship of the five individual types of leukocytes: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. The leukocyte differential count is compiled by counting 200–300 leukocytes in a stained dry blood smear. (Regarding the technique of compiling the differential count, see Hemogram.) The leukocyte differential count is subject to significant fluctuations even in healthy individuals, namely: Types of leukocytes In % Absolute figures Neutrophils........... 60-75 4,200-5,250 Eosinophils........... 2-5 140-350 Basophils............ 0.5-1 35-70 Lymphocytes........... 25-35 1,750-2,450 Monocytes........... 5-8 350-560 (The calculation of the absolute number of individual types of leukocytes is based on 7,000 leukocytes per 1 mm³.) The given table does not reflect the leukocyte differential count in children. According to Kononova's data, processed by the method of variational statistics, the leukocyte differential count of newborns 2 hours after birth is almost identical to that of placental blood and is distinguished by significant neutrophilia and a nuclear shift to the left; neutrophilia decreases by the 4th day after birth (see table in the article Leukocytosis). Later, the leukocyte differential count of an infant changes: neutrophilia drops, yielding to lymphocytosis. Thus, according to Sokolova-Ponomareva's data, the average figures for individual leukocytes at the age of 1 to 12 months are as follows: eosinophils—3.5%, neutrophils—37.4% (of which young—6.6%, band-nuclear—4.6%, segmented-nuclear—26.2%), lymphocytes—56.4%, large monocytes—2.7%. With age, the formula begins to gradually approach that of adults. A differential count alone, without counting the total number of leukocytes in 1 mm³ of blood, does not give a correct representation of the real ratios of individual forms of leukocytes; the frequently observed percentage increase in the number of lymphocytes (above 35–40%) does not indicate pathological lymphocytosis at all if the total number of leukocytes is reduced. On the other hand, a normal percentage of neutrophils during leukopenia actually signifies pathological neutropenia. Thus, only when the total number of leukocytes is known can one state, on the basis of the differential count, whether there is a pathological increase or decrease in a particular form of leukocytes. The main significance of the leukocyte differential count boils down to the fact that it gives an idea of the reaction of hematopoietic organs to various physiological and pathological processes in the body. At the same time, the number of lymphocytes reflects mainly the reaction of lymphoid tissue, and the number of neutrophils reflects the reaction of myeloid tissue. Many currently share the opinion that the number of monocytes reflects the state of the reticuloendothelial system, but this opinion cannot yet be considered definitively established. The changes in the leukocyte differential count observed in the clinic boil down to changes in individual types of leukocytes and represent separate forms of leukocytosis: neutrophilic, eosinophilic, and basophilic leukocytosis, lymphocytosis, and monocytosis. Neutrophilic leukocytosis, i.e., an increase in the number of neutrophils, is a regular phenomenon in almost all increases in the total number of leukocytes ("neutrophilic leukocytosis"), but it can also take place with a normal total number of leukocytes ("neutrophilia"), and sometimes is observed even with a decrease in the total number of leukocytes ("neutrophilic hypoleukocytosis"). All pathological leukocytoses, namely infectious and inflammatory, toxic, posthemorrhagic, tumor-related, are predominantly neutrophilic leukocytoses. The leukocytosis of newborns is of the same nature. Clinicists currently attach great importance to the combination of data on the total number of leukocytes and qualitative changes in neutrophils. In pathological states, both changes on the part of the nucleus, the so-called "nuclear shifts" (Arneth, Schilling), and changes on the part of the protoplasmic granulation (Naegeli, Freifeld) are observed. The nuclear shift of neutrophils was first thoroughly studied by Arneth. He divided all neutrophilic leukocytes into 5 main classes according to the segmentation of the nucleus. To class I he assigned neutrophils with an unsegmented nucleus, and to classes II–V neutrophils having respectively 2–5 segments. Arneth further divided these main classes into subclasses. Thus, in class I he distinguished myelocytes (M), neutrophils having an unsegmented nucleus with a slight indentation ("wenig gebuchtete") (W) and with a deep indentation ("tief gebuchtete") (T). In classes II–V Arneth also distinguished a number of subclasses depending on the shape of each segment. Thus, besides the 5 main classes, Arneth distinguished up to 80 subclasses. In normal blood, the majority of leukocytes belong to classes II–IV and only an insignificant number to class I (3–5%) and class V. In the majority of infectious diseases, Arneth observed an increase in the number of class I and II neutrophils, i.e., a "shift of the neutrophilic blood picture to the left." A shift to the right, i.e., an increase in multi-segmented neutrophils, is rare and has much less practical significance. According to Arneth, a shift to the left denotes an increased entry into the blood from the bone marrow of immature forms of neutrophils, which ordinarily occurs during increased destruction of the most mature neutrophils. Thus, Arneth judged the maturity of neutrophils by the segmentation of the nucleus, considering unsegmented neutrophils to be young and the most segmented ones to be the most mature cells; this introduces the basic principle of Arneth's doctrine. But in reality, there is often no parallelism between the youthfulness of a neutrophil and the degree of segmentation of its nucleus. The immaturity of a cell is easiest to establish by the structure of the nucleus. A young nucleus containing little basichromatin is distinguished by a pale coloration. In a matured nucleus, however, basichromatin and oxychromatin are sharply demarcated, and the nucleus looks darker and more differentiated when stained. Myelocytes, classified as class I, are undoubtedly young cells, but this cannot be said of every neutrophil that has an unsegmented nucleus and is therefore also classified in the same class. By the structure of the nucleus, it can easily be established that there are mature neutrophils with an unsegmented nucleus and less mature ones with a segmented nucleus. It can also be considered established that there are no fundamental differences between classes II and V (Pappenheim, Brugsch, Schilling). Thus, Arneth's doctrine in its main part is not entirely correct. Moreover, Arneth's classification is so cumbersome that it is difficult to apply in practice. Currently, Schilling's classification is widely distributed. It is fundamentally more correct and, moreover, significantly simpler than Arneth's classification. Class I (the most important) of Arneth was divided by Schilling into three groups: myelocytes (M), young forms (Y), and band forms (B); classes II–V he combined into one group of segmented forms (S). Thus, Schilling distinguishes a total of 4 groups of neutrophils. (Regarding the morphology of myelocytes, see Myelocytes and Leukocytes.) Young neutrophils are characterized by an unsegmented sausage-shaped or kidney-shaped nucleus; this nucleus does not stain intensively, but nevertheless it is very clearly differentiated with often strongly prominent nucleoli; their protoplasm mostly does not differ from the protoplasm of mature cells, though sometimes it has a light blue tint (when stained by Giemsa). This cell is apparently identical with Pappenheim's metamyelocyte. In normal blood, young neutrophils are encountered only in single instances (up to 1%). Band (band-shaped) neutrophils are characterized by an unsegmented, narrow, ribbon-like nucleus of T-, V-, or U-shape. The structure of the nucleus is clearly differentiated, and the nucleus contains no nucleoli. Such are normal band-shaped neutrophils; in normal blood they are encountered in an amount of 3–5%. Schilling also distinguishes "pathologically-degenerative" forms of band-shaped neutrophils, characterized by a "narrow, ribbon-like, often strangely curved and always hyperchromic (structureless-dark) shape of the nucleus." Segmented neutrophils make up the largest number of blood leukocytes (60–72%); their nuclei usually consist of 2–5 segments connected by very delicate threads or wider bridges. Currently, the percentage relationships of the four neutrophil groups characterized above are almost always included in the leukocyte differential count (see also Hemogram). Depending on the ratio of these four groups of neutrophils, Schilling distinguishes the following forms of neutrophilic leukocytosis. 1. Neutrophilic leukocytoses without a nuclear shift are observed among physiological leukocytoses in digestive and sometimes in static leukocytosis; and among pathological leukocytoses—in posthemorrhagic leukocytosis, chlorosis, polyglobulia, in mildly proceeding infectious processes, in acute polyarthritis (even in severe cases), in tetanus, in uncomplicated malignant neoplasms, after many medications and the infusion of physiological saline. Neutrophilia (a percentage increase in neutrophils with a normal total number of leukocytes) without a nuclear shift is observed inconsistently in chlorosis. 2. Neutrophilia with a simple hyporegenerative shift denotes an increase in the percentage of only band-shaped forms with a small increase in the total number of leukocytes.

This form of shift is usually observed in mildly proceeding acute infections, protozoan diseases (e.g., in malaria during a paroxysm), in superficial and encapsulated abscesses, mild catarrhal appendicitis, in open suppurations of the eye, ear, larynx, in chronic endocarditis, chronic sepsis, in necrotizing malignant tumors, in lymphogranulomatosis, in active, mildly proceeding tuberculosis, especially tuberculosis of serous membranes and glands. This form of leukocytosis often has great practical significance, because it helps to ascertain a latent infection where the process clinically appears to be cured (e.g., in mild forms of active tuberculosis, chronosepsis). 3. Neutrophilic leukocytosis with an unquestionably regenerative shift denotes already a certain increase in stab neutrophils (up to 2-15%) and even myelocytes (up to 1-2%); at the same time, the total leukocyte count is usually significantly increased. With a larger increase in the number of myelocytes, this shift is called hyperregenerative. This form of neutrophilic leukocytosis is observed upon the intensification of all those processes that were indicated in the previous group. Of physiological states, this form is encountered sometimes in pregnancy and during prolonged muscular work; it is observed in severe intoxications (with lead, sublimate, illuminating gas, lysol, phenylhydrazine, etc.), in significant exacerbations of chronic infections (tuberculosis, sepsis, and endocarditis), in septic complications of those diseases that ordinarily proceed without nuclear shifts or else with an insignificant or degenerative shift (e.g., typhoid fever, measles, dengue fever, yellow fever, influenza, syphilis, tuberculosis, malignant tumors), as well as in acute nutritional and digestive disorders in infants. 4. Neutrophilia with a degenerative shift denotes an increase in the number of band neutrophils, mainly degenerative forms, not accompanied usually by an increase in young forms; at the same time, the total leukocyte count is decreased. This form is encountered usually in mixed infection (typhoid complicated by sepsis; tuberculosis complicated by secondary infection) and in very chronic or low-virulence cases of sepsis (e.g., recurrence of a liver abscess, endocarditis). When examining leukocytes for the leukocyte differential count, the state of the protoplasmic granularity of the neutrophils deserves attention. In infectious processes, the granularity of neutrophils is often stained very sharply, acquiring thereby the appearance of coarse grains, sometimes of separate clumps. Naegeli considers such neutrophils to be toxicologically altered. This so-called toxicity of neutrophils is best revealed not by azure-eosin staining, but by carbol-fuchsin-methylene blue according to Freyfeld. The more sharply expressed the intoxication of the organism, the more sharply expressed is usually the granularity of the neutrophils. Neutrophilic, sharply expressed leukocytosis does not necessarily entail a severe prognosis; it testifies only to a sharp enhancement of the function of myeloid tissue. On the other hand, insignificant neutrophilia in diseases running ordinarily with neutrophilic leukocytosis indicates either the mildness of the infection or, conversely, a hypertoxic form; the general clinical picture and sometimes the character of the nuclear shift help to sort this out. Eosinophilic leukocytosis (eosinophilia). The only acute infectious disease proceeding often at the height of the illness with an increase in the number of eosinophils alongside an increase in the total leukocyte count is scarlet fever in children. Usually, however, in blood containing an increased number of eosinophils, the total leukocyte count is not increased, which is why eosinophilic leukocytosis is more often called eosinophilia. Eosinophilia is observed very frequently in helminthic diseases. In trichinosis, eosinophilia is particularly sharply expressed, reaching even 80%, but in very severely proceeding trichinosis, eosinophilia may be absent. Eosinophilia is frequently observed in skin diseases: eczemas, psoriasis, pemphigus, prurigo; in convalescents in the post-infectious and post-intoxication periods; in anaphylactic and so-called anaphylactoid states: serum sickness, hay fever, urticaria, bronchial asthma, colitis membranacea, Quincke's edema; in children: in the so-called exudative diathesis, if the mentioned skin phenomena are present, in approximately 60% of cases; almost regularly in muscular rheumatism, sometimes in lymphogranulomatosis and malignant neoplasms; sometimes in fresh nephrosis, nephritis; occasionally in gonorrheal, especially gynecological diseases. The appearance in the blood of eosinophils—after their complete absence at the height of the disease—denotes the approach of the recovery period (typhoid fever, typhus, etc.). Often, eosinophilia is evaluated as a favorable prognostic symptom, but this must be done with great caution. Only in combination with the general clinical picture and other blood changes (lymphocytosis, absence of a nuclear shift of neutrophils or an insignificant shift, absence of an increase in the total leukocyte count) does eosinophilia have a certain favorable prognostic significance in acute infectious diseases and chronic tuberculosis. In chronic septic diseases, on the other hand, eosinophilia is sometimes observed despite a poor prognosis. In prolonged tuberculosis with fever, the number of eosinophils often does not decrease (Naegeli). Basophilic leukocytosis—an increase in the number of blood basophils (normally 0.5%, i.e., up to 40 per 1 mm³). An insignificant increase is observed sometimes in clinically healthy people. A more significant one sets in after the injection of foreign protein and after Pasteur treatment for rabies. An increase in basophils, varying greatly in degree, is encountered further in polycythemia (Naegeli), myeloid leukemia, aleukemic myelosis, constitutional hemolytic anemia (Alder), secondary anemia, sometimes in malignant neoplasms proceeding with significant anemia, hemophilia, chlorosis, and in convalescents after beriberi (Schilling). In constitutional hemolytic anemia, the number of basophils after extirpation of the spleen does not decrease, just as in myeloid leukemia after X-ray treatment. In diagnostic respects, basophilia can be used only very rarely. In prognostic respects, it must be pointed out that only in malignant anemia does the decrease in basophils run ordinarily parallel to the severity of the disease (Naegeli). Lymphocytosis—an increase in the number of blood lymphocytes. One must approach the evaluation of lymphocytosis very cautiously, because the number of blood lymphocytes is subject to large physiological fluctuations. At the same time, it must be remembered that even after mild infections, intoxications, and vaccinations, an increased number of lymphocytes can persist for months. Lymphocytosis, observed in many people during and after the war (so-called wartime and 653

LEUKOCYTE DIFFERENTIAL COUNT

postwar lymphocytosis), was apparently connected with nutritional conditions. But even now one not infrequently has occasion to observe 30-35% lymphocytes in people without clinically detectable pathological changes. A distinction is made between absolute lymphocytosis (when the number of blood lymphocytes exceeds 3,000) and relative lymphocytosis (when only the percentage content of blood lymphocytes is increased). A temporary, transient lymphocytosis may have at its basis a redistribution factor, such as, for example, myogenic leukocytosis, adrenalin leukocytosis (in certain stages). On the other hand, lymphocytosis in leukemic and aleukemic lymphadenoses occurs as a result of hyperplasia of the lymphatic apparatus. Lymphocytosis as a rule occurs in the post-infectious period, as well as the post-toxic period and in a number of infectious diseases: typhoid fever, epidemic parotitis, smallpox, whooping cough (especially in the catarrhal period), rubella, influenza, malaria, pellagra, dengue fever, chronic benign tuberculosis, syphilis. The origin of lymphocytosis in the just-listed group Naegeli explains by the increased function of the lymphatic system. Such an opinion would be correct if absolute lymphocytosis took place in these diseases. In reality, however, only in mumps is there a true lymphocytosis, whereas in smallpox the number of not only lymphocytes but also neutrophils is increased, and in typhus and rubella the total number of lymphocytes is either close to normal or somewhat decreased. In the majority of diseases proceeding with lymphocytosis, there is simultaneously also leukopenia, so that the total number of lymphocytes is rarely increased, while the number of neutrophils is decreased. It is therefore more correct to say that for the majority of these diseases what is characteristic is not lymphocytosis, but leukopenia (see) and neutropenia. Lymphocytosis is also caused by certain exogenous physical-chemical influences: prolonged mild exposures to X-rays (for example in roentgenologists), a quartz lamp, a unilateral diet of carbohydrates and fats. Absolute or relative lymphocytosis in combination with neutropenia is observed inconsistently in almost all internal secretory diseases (Addison's disease, diabetes, various forms of obesity, etc.). Many consider correct the opinion of Kocher that lymphocytosis is characteristic of Basedow's disease; this notion needs some restriction, since in Basedow's disease, especially in mild forms and initial stages, lymphocytosis may not be present at all. It is not yet clear whether lymphocytosis in diseases of the internal secretion organs is connected with an internal secretory influence on the lymphatic system or whether some other factors play a role here (the influence of the autonomic nervous system). Also unclear is the question of so-called constitutional lymphocytosis. Naegeli denies the existence of constitutional lymphocytosis, whereas Bauer recognizes it and regards constitutional lymphocytosis, respectively neutropenia, as a partial infantilism of the hematopoietic apparatus, "as a result of anatomical or functional hypoplasia of the granulocytic system." The role of the constitutional factor in the lymphocytic reaction Bauer supports by the facts that individual people react with lymphocytosis rather than neutrophilia to septic infections (Marchand and others), to purulent tonsillitis (Deussing). The significance of lymphocytosis is often reduced to the fact that it is supposedly a histological expression of the immunization of the organism (Besançon, Labbé). Such a viewpoint is groundless already because, as was indicated above, lymphocytosis is most often observed in leukopenias and consequently is for the most part relative. Monocytosis—an increase in the number of blood monocytes (normally 6-8%). It must be remembered that monocytosis can also be detected in a healthy person if one takes for examination the first drop of blood from the earlobe without prior rubbing of the latter (Schilling). Therefore Schilling recommends taking only the second or third drop from the earlobe after prior rubbing. Monocytosis is observed both with general leukocytosis and without it. In leukocytosis, monocytosis is noted in smallpox, in the later stages of typhus, in measles, rubella, epidemic parotitis, acute syphilitic and tuberculous processes, septic processes, many acute infectious diseases (more often in the crisis period); monocytosis is less pronounced in chickenpox, scarlet fever. In typhus, the number of monocytes increases sometimes to 20-30%. A sharply pronounced monocytosis is sometimes observed in so-called endocarditis lenta, in which the number of monocytes increases even to 30-40%; at the same time, special attention is drawn to the appearance in the blood of large reticuloendothelial cells, histiocytes, which in their morphology sometimes closely approach monocytes. Without leukocytosis (with a normal or lowered total leukocyte count), monocytosis is observed in protozoal diseases: malaria, kala-azar, relapsing fever, septic processes, so-called Banti's disease, measles, yellow fever, dengue fever, sympathetic ophthalmia, poliomyelitis, pellagra. In chronic malaria, the number of blood monocytes increases sometimes to 40%. Such sharp monocytoses are observed occasionally in anginas (so-called "monocytic anginas") and chronic sepses, which some (Marchand, Schultz, Baader and others) explain by specific features of the causative agents. Although there exists such a causative agent, the so-called Bacterium monocytogenes, with which it is always possible to induce experimental monocytosis in rabbits, nevertheless the explanation of monocytic reactions in humans exclusively by the features of the causative agent is far from sufficient; a large role must be attributed to the features of the macroorganism. Regarding the origin of monocytoses, it must be said that some (Pappenheim and others) tried in the clinic to gather evidence speaking for their origin from the lymphatic system, while others (Naegeli and others)—for their origin from myeloid tissue. However, an increase in the number of monocytes can go parallel either to an increase in the number of neutrophils (e.g., in sepsis) or to an increase in the number of lymphocytes (e.g., in protozoal diseases). At the present time, in accordance with the doctrine of the origin of monocytes from the reticuloendothelial cell (Aschoff-Kiyono), the majority of clinicians view monocytosis as the result of an increased functional state of the reticuloendothelial system. According to this notion, histiocytes sometimes encountered in the blood (e.g., in certain septic diseases) are related to monocytes. Schilling calls them "atypical monocytes." The increased content of these cells in the blood, in the opinion of some, is of central origin, and Schilling was indeed able to note hyperplasia of the reticuloendothelial cells of the liver, spleen, and bone marrow. In the opinion of others (Bittorf, Deneke), these cells have a peripheral origin from the endothelium of blood vessels. The viewpoint shared at present by many regarding the commonality of monocytes and histiocytes, and the origin of monocytoses from the reticuloendothelial system cannot yet be considered conclusively proven (Maximow, Bloom). The significance of monocytosis is reduced to the fact that in acute infectious diseases the increase in the number of monocytes, which for the most part is parallel to the general increase in the number of leukocytes, usually represents a favorable prognostic sign. This cannot be said in relation to chronic septic diseases. In protozoal diseases, monocytosis has diagnostic significance.