The Hemopoietic organs include the bone marrow, spleen and lymphoid tissue as well as the circulating blood.

In early fetal life the yolk sac, liver and spleen are sites of blood formation but by 5 or 6 months the bone marrow is the sole organ of hemopoiesis. In infants all the bones but in the adult only the vertebrae, pelvis, sacrum, skull and proximal ends of the femur contain hemopoietic marrow.

Erythrocytes, leukocytes and platelets are derived from a pluripotent stem cell. Many glycoprotein hormones regulate proliferation and differentiation of the progenitor cells and the function of the mature blood cells. These include:

Erythropoietin is produced predominantly in the kidney. Recombinant human erythropoietin is a potent therapy for some anemias, particularly for patients on dialysis for chronic renal failure. Other growth factors are produced by many cells, particularly T lymphocytes, monocytes, macrophages, endothelial cells and fibroblasts.

Diseases of Red Cells

These are anemias (too few cells) and polycythemia (too many cells).

ANEMIAS

Definition: Reduction in the number of circulating red cells (red cell mass) below a normal reference range.

Signs and Symptoms of Anemia

1. Dyspnoea and palpitation on exertion or at rest depending upon the severity of the anemia.
2. Signs of congestive heart failure
3. Hypoxia of the central nervous system with insomnia, inability to concentrate and disorientation.
4. Aggravation of ischemic vascular disease including angina pectoris, heart failure, claudication, CNS and gastro-intestinal symptoms.
5. Pallor of mucus membranes and skin.

Anemia is diagnosed by counting the red cells and measuring their hemoglobin content.

Modern laboratories use electronic cell counters in place of older manual methods. These instruments count the red cells, measure their volume and hemoglobin content and calculate indices that are used to characterize abnormalities of the cells.

The three red cell parameters measured by the electronic cell counters are:

The following indices are calculated.

Hematocrit (Hct) = RCC x MCV (This is equal to the packed cell volume measured by centrifugation)

Mean Cell Hemoglobin (MCH) = Hb/RCC in pg. (picograms)

Mean Cell Hemoglobin Concentration (MCHC) = Hb/Hct x 100 in g per dL.

Red Cell Distribution Width (RDW) = SD/MCV x 100 (Coefficient of Variation)

These indices will characterize the cells as:

The RDW is a numerical measure of the variation in red cell volume (size). More than average variation is known as anisocytosis.

These indices correlate with the appearance of the red cell under the microscope but are frequently more reliable than subjective observation.

Anemias can be classified in two ways

1. Morphological Classification:

(A) Normochromic normocytic or with anisocytosis. Most anemias are in this category.

(B) Hypochromic microcytic anemias are due to lack of either:

(C) Macrocytic normochromic anemias due to abnormalities of DNA synthesis. Lack of Vitamin B12, folate, myelodysplastic syndromes and thyroid deficiency are the chief causes.

2. Patho-physiological Classification

Red cells survive only 100-120 days in the circulation. Therefore blood loss, reduced production or decreased survival can cause anemia very rapidly.

All anemias can be classified into one or a combination of two or more of the following categories.

(A) Blood loss, acute or chronic

(B) Increased rate of destruction (Hemolytic anemias)

(i) Intrinsic abnormalities of the red cell

Inherited abnormalities of :

Red cell membrane
Red cell enzymes
Hemoglobin synthesis
Acquired abnormality of: red cell membrane (PNH)

(ii) Extrinsic (to the red cell) abnormalities

Antibody mediated
Medications and drugs
Mechanical trauma
Infections
Chemical toxins
Sequestration (eg in spleen)
Disseminated intravascular coagulation (DIC)

(C) Impaired red cell production

(i) Defective hemoglobin synthesis (Heme or globin - see above)
(ii) Defective DNA synthesis
(iii) Stem cell defectsii.
(iv) Marrow invasion by leukemia, lymphoma, metastatic tumor, fibrosis, granulomas etc.
(v) Unknown or multiple mechanisms

The reticulocyte count is a useful test of marrow activity. Reticulocytes circulate is the blood for 2 or 3 days. Their numbers reflect the rate of erythropoiesis in the marrow. In anemia due to impaired production reticulocyte counts are low. In most other anemias the count is high unless marrow activity is inhibited by secondary mechanisms additional to the primary cause of the anemia.

NOTE: The absolute reticulocyte count is a more reliable indicator than the percentage of reticulocytes in the red cell population. Automated cell counters calculated both values.
The count should be corrected for the "shift" in reticulocyte from the marrow to the peripheral blood that occurs in anemic patients. A rough guide is to halve the uncorrected count to correct for the "shift".

THE APPROXIMATE FREQUENCY OF THE VARIOUS ANEMIAS SEEN IN HOSPITAL PRACTICE IS

40% = Anemias of inflammation and chronic disorders
20% = Iron deficiency anemias
15% = Acute bleeding
16% = Marrow damage
8% = Maturation disorders
7% = Hemolytic anemias

BLOOD LOSS ANEMIA (Classification 2A)

Acute blood loss causes a normochromic normocytic anemia. Chronic loss often causes a hypochromic microcytic iron deficiency anemia and will be discussed below.

 
ANEMIAS DUE TO IMPAIRED RED CELL PRODUCTION (Classification 2C)

Iron deficiency anemias (Classification C i)

1. Chronic blood loss usually from gastro intestinal, genito urinary tracts or post-traumatic. Common causes are peptic ulcers, hemorrhoids, polyps, cancer and vascular lesions of the bowel, nose bleeds, inflammatory bowel disease, uterine bleeding etc.

2. Increased requirements

Menstruation
Pregnancy
Infancy, adolescence

3. Malabsorption (celiac disease, sprue, phytates in food etc.)

4. Poor diet.

5. Hemosiderin loss: Pulmonary siderosis, hemosiderinuria

 

The pathogenesis of iron deficiency is shown in Figure 7.7 (page 17)

 
Sideroblastic anemias result from impairment of porphyrin synthesis (Classification C iii)

This may be due to inhibition or deficiency or one or more of the enzymes of the porphyrin biosynthetic pathway. Causes are alcohol, lead, drugs such as INH, inherited enzyme defects or acquired stem cell disorders (myelodysplastic syndromes). The result is a hypochromic or normochromic anemia with accumulation of iron containing granules in the mitochondria of the marrow normoblasts forming a ring of granules around the nuclei.

Vitamin B12 and Folate deficiency (Classification C ii)
These vitamins are essential for the normal synthesis of nuclear DNA. Deficiencies result in abnormalities of dividing cells throughout the body. Hemopoietic cells divide rapidly and therefore impaired DNA synthesis causes anemia by a double "whammy". The production of cells is reduced and the rate of destruction is increased because the cell structure is distorted.

The biochemical roles of vitamin B12 and folate is shown in figures 4.5 (page 17)

Vitamin B12 and Folate Balance

Folate stores are depleted in 3-4 months, vitamin B12 in 3-4 years after intake ceases. Folate is absorbed in the small intestine, vitamin B12 requires intrinsic factor from the stomach and is absorbed in the terminal ileum.

Causes of Vitamin B12 and Folate deficiency

(1) Inadequate intake

Folate - lack of fresh vegetables (old age, institutions, poverty, famine, special diets)
B12 - lack of meat and dairy products (vegans), Pernicious Anemia (See below).

 
(2) Increased requirement for folate

Pregnancy and puerperium
Infancy
Hemolytic anemia, leukemia, myelo-proliferative disease, malignancies, tuberculosis, rheumatoid arthritis, chronic inflammatory diseases

(3) Malabsorption

Folate: Small bowel disease (celiac, sprue , Crohn's disease, ileal resection, etc.)

B12: Pernicious anemia, "Blind loops" of gut, gastrectomy (total or sub-total), fish tape worm, Crohns disease, ileal resection, tropical sprue.

(4) Impaired utilization of folate

Anti-folate chemotherapeutic drugs, anti-convulsants, sulphasalizine.

(5) Mixed Mechanisms

Liver disease, alcoholism, intensive care, parenteral feeding and congestive heart failure.

Pernicious anemia is an auto-immune disease in which the parietal cells of the stomach are destroyed and the intrinsic factor (I.F.) from these cells is inactivated by antibodies. The vitamin therefore cannot be absorbed in the terminal ileum.

This results in a macrocytic anemia and a megaloblastic transformation in the marrow with severe anemia, leucopenia and thrombocytopenia. The serum vitamin B12 level is low and anti parietal cell and anti I.F. antibodies are present in the serum.

Diagnosis is confirmed by proving the absence of I.F. This can be done by showing that a lack of B12 absorption can be corrected by IF (Schillings Test). Treatment requires life long injections of vitamin B12.

Blind loops of small intestine due to adhesions or other causes result in bacterial overgrowth. The bacteria can then utilize available vitamin B12 and cause deficient absorption.

Celiac Disease and Sprue
Celiac disease is a malabsorption syndrome caused by a sensitivity to gluten, - a protein present in wheat, barley, rye and oats, (corn and rice do not contain gluten). The effect of ingesting gluten is to cause villous atrophy in the jejunum and ileum with consequent malabsorption of fats, fat soluble vitamins, some carbohydrates and B vitamins including folate and B12. A gluten free diet leads to recovery of the villi and normal absorption. Antibodies to gluten/gliadin and endomysium are present in the serum.

Tropical sprue is a malabsorption syndrome of unknown causes associated with villous atrophy similar to celiac disease. It is found in tropical regions of Central and South America and other areas of the world.

 
 
Aplastic anemia (Classification C iii)
Failure of stem cell proliferation and/or differentiation can result in a pancytopenia. Inherited causes include Fanconi or non-Fanconi aplastic anemia. The Fanconi type is associated with skeletal, renal or other inherited anomalies. Acquired aplasia is frequently idiopathic. Known causes include drugs especially those with a benzene ring eg. chloramphenicol, radiation, infections including viral hepatitis and other viruses and a variety of toxins, insecticides and industrial chemicals (benzene and other). The red marrow may be replaced partially or completely by fatty marrow. In hospital practice cancer chemotherapeutic agents are an important cause of marrow hypoplasia and aplasia.

Pure Red Cell AplasiaMay also be inherited (Diamond-Blackfan syndrome) or acquired. The latter group may be idiopathic, associated with thymomas and lymphomas or with infections. Parvovirus has a propensity to invade erythroid precursors and causes sudden red call aplasia. Patients with sickle cell disease may succumb to this. Drugs and riboflavin deficiency have also been implicated.Myelo-dysplastic syndrome (Classification C iii)

This is a group of disorders of the marrow stem cell which present with pancytopenia. These patients usually have chromosomal abnormalities in the stem cell and may develop acute leukemia as the disease progresses. Anemia is a major feature and is often macrocytic.

The following sub-categories are recognized:a. Refractory anemia with or without ring sideroblasts (RA or RARS)b. Refractory anemia with excess "blasts" (RAEB)c. Refractory anemia with excess "blasts" in transformation (RAEB-IT). Many hematologists regard these cases as acute leukemias.

Anemia of chronic disorders (Classification C v)
Many acute and chronic inflammatory, granulomatous, collagen vascular and auto-immune disorders are accompanied by anemia. In hospital practice this is a very common cause of anemia. The anemia is due to impaired production of red cells, reduced utilization of iron and increased destruction of red cells in reticulo-endothelial cells.

(1) Inadequate release of iron from reticulo-endothelial cells
(2) Release of interferon, interleukins and TNF from monocyte-macrophages with inhibition of erythropoietin production and of proliferation and differentiation of erythroid progenitors.
(3) Increase destruction of older red cells in active reticulo-endothelial tissues.

The anemia is often hypochromic but iron stores and ferritin levels are raised and serum iron and iron binding capacity are low. The anemia responds to successful treatment of the underlying disease or erythropoietin therapy in some cases.

 Anemia of renal disease (Classification C v)

Multiple factors operate

(1) Reduced production of erythropoietin
(2) Inhibition of marrow activity by renal failure to excrete metabolic products.
(3) Mild to moderate hemolysis in some cases
(4) Plasma volume expansion especially in nephrotic syndromes.
(5) Blood loss and aluminum excess due to dialysis.

Many cases respond well to recombinant human erythropoietin by injection.

Anemia due to endocrine deficiencies (Classification C v)

Deficiencies of pituitary, adrenal, testicular, ovarian and thyroid hormones are often associated with anemia.

HEMOLYTIC ANEMIAS (Classification 2 B)

Pathophysiology of Hemolysis

1. Marrow erythropoiesis is usually increased.
2. Production of Reticulocytes is increased and nucleated red cells may enter the circulation.
3. Red cell survival is reduced.
The balance between reduced red cell survival and increased marrow activity will determine whether the red cell count falls (anemia) or is maintained by the compensatory hyperplasia.
4. The levels of unconjugated (indirect) bilirubin in the serum and urobilinogen in the urine increase. Bilirubin (direct) does not increase in serum or urine.
5. Serum haptoglobin binds released hemoglobin and is removed by the R-E system.
6. Lactic acid dehydrogenase (LDH) serum levels rise due to release from red cells.
7. Serum iron may rise.

INTRINSIC DISORDERS OF THE RED CELL (Classification B i) See Page 3

ACQUIRED DISORDERS

Paroxysmal Nocturnal Hemoglobinuria is the only hemolytic anemia due to an acquired intrinsic disorder of red cells.
This is a rare acquired disorder of the marrow stem cell. The result is a defect of the cell membrane which causes the cells to become abnormally sensitive to destruction by complement factors especially when the pH is lowered. The primary cause is unknown. Patients develop a chronic hemolytic anemia complicated quite often by thrombo-embolic phenomena and sometimes by aplastic anemia and leukemia. A classical sign of the disease is the passage of "Coca-Cola" urine on rising in the morning due to the presence of hemoglobin in the urine.

 
INHERITED DISORDERS

MEMBRANE DEFECTS
Hereditary spherocytosis is due to a defect in the red cell cytoskeleton resulting in loss of portions of membrane with consequent "sphering" of the cells. Cell deformability is reduced so that passage through splenic sinusoids is slow and many cells are hemolyzed. Diagnosis is confirmed by demonstrating increased osmotic fragility and rapid auto-hemolysis when the cells are incubated at 37oC (Figure 4.16 page 18). The hemolysis and most of the clinical manifestations are cured by splenectomy.

Other defects of the cytoskeleton can produce hereditary elliptocytosis of which there are many varieties. Some are associated with hemolysis, others not.

ENZYME DEFECTSDeficiency of Glucose 6 Phosphate Dehydrogenase (G6PD) is the commonest. This is a sex linked disorder. Female heterozygotes are largely unaffected but male hemizgygotes are abnormally sensitive to oxidative drugs and toxins and develop acute hemolysis on exposure. Important agents are some anti-malarial drugs, analgesics, fava beans, sulfonamides, naphthol and infections but there is a long list of potential lytic agents. G6PD acts on the Pentose shunt. Enzyme defects of the Embden-Meyerhof pathway causing hemolysis include pyruvate kinase, glucose 6-phosphate isomerase, hexokinase and several others.DEFECTS OF HEMOGLOBIN SYNTHESIS
THALASSEMIA These are inherited conditions in which there is a reduced rate of synthesis of one or more of the globin chains. Production of globin chains during fetal and adult life is shown in Figure 3.6 (page 18).

BETA THALASSEMIA

In Bo Thalassemia there is total absence of B chain synthesis whereas in the form some B chain synthesis occurs. Approximately 100 different gene mutations can produce these defects. Gene deletions are uncommon. Mutations may involve the promoter region, the chain terminator, cause aberrant splicing or other mechanisms. The red cells are defective because they lack sufficient hemoglobin. In addition free alpha chains, accumulate since there are too few beta chains with which to pair. The free alpha chains form insoluble inclusions and damage the cell membrane.
The clinical effects are summarized in Fig. 5.2 (page 10A). In Thalassemia Major there is hyperplasia and expansion of the erythroid marrow with thinning of cortical bone and massive enlargement of spleen and liver. The severe anemia requires frequent blood transfusion. This together with increased iron absorption due to the anemia and marrow hyperplasia frequently results in massive iron overload, with consequent diabetes, hepatic and cardiac failure. The morbidity and mortality from these complications is high but can be prevented by daily IV infusion of an iron chelating agent. Thalassemia Minor is asymptomatic with mild anemia

.ALPHA THALASSEMIA

There are four alpha globin genes. Deletions of one or more of these causes the syndromes shown in Fig. 5.2. The most severe form, hydrops fetalis, is lethal in utero. It is seen in the Asian but not in the African form and is due to deletion of all four genes, two from each chromosome 16. Deletion of both genes from a single chromosome rarely if ever occurs in the African form.

Thalassemia occurs in the Far East, Middle East and India as well as in the Mediterranean region.Delta Beta Thalassemia involves impairment of both delta and beta chain synthesis.
 
HEMOGLOBINOPATHIES

These diseases are due to abnormalities of the hemoglobin molecule involving amino acid substitution in one or other of the globin chains.

The most frequent of the these involve the beta chain. In Sickle Hemoglobin valine and in Hemoglobin C lysine is substituted for glutamic acid at position 6 of the beta chain. Both genes are found particularly in West Africa and approximately 8% of African Americans are heterozygous for the Sickle gene. HbC is approximately one tenth as common.

Heterozygotes for Hb S are usually heathy but pathological effects can occur under conditions of severe hypoxia. This is known as the Sickle Trait and for example can cause symptoms in unpressurised aircraft or after severe exertion.

The homozygotes develop symptoms only after birth since in utero and in infancy the presence of fetal hemoglobin reduces the tendency of red cells to form sickles. As the child develops the proportion of HbS approaches 100% and the Sickle Hemoglobin will polymerize, form crystals and distort the red cell particularly in areas of low oxygen tension. This results in a hemolytic anemia and microvascular occlusions with widespread ischemic changes. The marrow is hyperplastic and initially the spleen is enlarged. Later the ischemic effects cause infarcts in the spleen with subsequent fibrosis and ultimately complete disappearance of the spleen. Infarcts also occur in bones, brain, kidney, lung, liver, retina, skin and sub-cutaneous tissue.

The clinical course until recently resulted in chronic pain, recurrent crises, much misery and death in childhood or adolescence. A particular danger is the aplastic marrow crisis associated with parvovirus and other viral infections. Patients may die due to rapid destruction of all their red cells when marrow production ceases if transfusions are not given soon enough. In recent decades the management has improved and most patients live into adult life and middle age but chronic morbidity is still a trial for patients and their families.
The effects of hemoglobin C are milder than HbS but hemolysis and complications do occur in the homozygous subject. Combinations of HbS and HbC with each other and with various forms of Thalassemia occur and cause a variety of clinical syndromes.

More than one hundred genetic abnormalities of the globin chains are known. Some are common in particular regions of the globe and others are quite rare.

EXTRINSIC (TO THE RED CELL) DISORDERS (CLASSIFICATION B ii) See Page 4

ANTIBODY MEDIATED HEMOLYTIC ANEMIAS

(a) Auto-immune hemolytic anemias
Most are idiopathic (60%) but some are secondary to lymphomas, leukemias, other neoplasms, other auto-immune diseases (SLE) and drugs. These are characterized by the presence of antibodies on the red cell surface detected by the Coombs Test (Figure 4.32, page 18).

Warm antibodies react at 37oC, are IgG globulins and fix complement.

Drug induced hemolytic anemias are an important group. Mechanisms implicated include a hapten model, immune-complexes causing an "innocent bystander" reaction on the red cell and auto-antibody induction.

Cold agglutinins are active between 0o and 30oC and cause agglutination and sometimes hemolysis in peripheral and colder regions of the body. They may occur with mycoplasma and EB virus infections and some lymphomas or without obvious cause.

Paroxysmal cold hemoglobinuria is caused by an unusual antibody which binds to red cells at low temperatures, fixes complement and causes hemolysis when the temperature is raised to 30oC. It may be associated with Syphilis.

(b) Alloimmune hemolytic anemias
Incompatible transfusion reactions and hemolytic disease of the newborn will be discussed in the lectures on Blood Transfusion.

Mechanical Trauma to red cells

Mechanical damage to red cells can be produced by arterial grafts and cardiac valves as well as micro-thrombi in small vessels. The latter are known as micro angiopathic hemolytic anemias and are seen in thrombotic thrombocytopenic purpura, disseminated intravascular coagulation, hemolytic uremic-syndrome, sepsis and a variety of clinical states.

March hemoglobinuria occurs in the military, African Bongo drummers, long distance runners, karate experts and others whose hands or feet are subjected to repetitive trauma.
 
Infections causing hemolysis include malaria and clostridia. Chemical and physical agents such as drugs, industrial and domestic chemical substances and burns can also cause hemolysis. Splenic sequestration due to splenomegaly of any cause can result in a hemolytic anemia.

POLYCYTHEMIA

Polycythemia refers to an increased concentration of red cells.

Relative Polycythemia refers to a reduction in plasma volume. This may be acute due to fluid loss or chronic. The latter is seen in Gaisbock's syndrome or Stress Polycythemia. This is associated with hypertension and its etiology is unknown.

Absolute Polycythemia may be primary or secondary. Primary polycythemia or Polycythemia Vera is a myelo-proliferative disorder with proliferation of myeloid stem cells. Erythropoietin levels are normal or low. Polycythemia secondary to hypoxic cardiac or pulmonary disease is caused by increased production of erythropoietin. Erythropoietin secreting tumors can also produce secondary polycythemia. Examples are some renal carcinomas, hepatomas and cerebellar hemangio-blastomas. Some abnormal hemoglobin molecules bind oxygen more avidly than HbA. The resulting tissue hypoxia causes increased erythropoietin production and polycythemia.

NON MALIGNANT DISORDERS OF LEUKOCYTES 

Neutrophil leukocytes
An increase in neutrophil leucocyte count above 7.5 x 109/liter is called a neutrophilia. Frequently this is accompanied by increased numbers of band cells and sometimes earlier precursor cells and is known as a "shift to the left". The neutrophils may also show toxic-granulation and Dohle bodies. Common causes of neutrophilia are many bacterial infections, inflammations and tissue necrosis (for example myocardial infarction). Other causes include neoplasms, acute hemorrhage, hemolysis, trauma and other stress inducers, cortico-steroids myeloproliferative diseases and myeloid growth factor administration (for therapy) or excessive production of growth factor from some tumors.

A leukemoid reaction is an increase in leukocytes in the peripheral blood usually accompanied by circulating immature precursor cells due to causes other than leukemias. Examples are some severe or chronic infections, hemolysis and metastatic cancer. Tuberculosis and chronic suppurative lesions such as osteomyelitis are good examples. Most often neutrophils and their precursors are involved and the blood can mimic chronic myeloid leukemia (CML). The absence of toxic granulation and Dohle bodies, a low neutrophil alkaline phosphatase and increased numbers of basophils and eosnophils favor CML whereas the reverse of these findings points to a leukemoid reaction. Lymphocytic and rarely monocytic leukemoid reactions can also occur.

Eosinophilic leucocytosis
Eosinophil counts above 0.4 x 10⁹/liter are called eosinophilias. Allergic diseases including asthma, hay fever, urticaria and food sensitivity are probably the commonest causes. Parasitic diseases rank next. In the USA tapeworms, ascariasis, pin worms and trichinosis are common causes. Amebiasis, hookworm, filariasis and schistosomiasis are common in tropical areas. Less common causes are many skin diseases, convalescence from acute infections, drug sensitivities, polyarteritis nodosa, pulmonary eosinophilia, hypereosinophilic syndrome, Hodgkins disease, other tumors and eosinophilic leukemia.

Basophil leukocytes
Blood basophil counts above 0.1 and 109/liter are called basophilias. These are rare but may be seen in CML, polycythemia vera, myxedema, small pox, chicken pox and ulcerative colitis.

Neutropenia
The lower limit of normal neutrophil counts is 2.5 x 109/liter but in many normal Black and Middle Eastern subjects the lower level is often 1.5 x 109/liter. As absolute neutrophil count under 0.5 x 109/liter predisposes to recurrent infections and counts under 0.2 x 109 liter pose the threat of devastating or lethal infections.

Neutropenia can be congenital and potentially lethal in infancy. Kostman's disease is an example. Acquired causes are much more frequent. The commonest causes are a variety of drug including many commonly used anti inflammatory agents, antibacterals anti-convulsants, antithyroids, hypoglycemics, phenothiazines, psychotropics and a long list of other medications.

A number of infections can be accompanied by neutropenia. Viral infections including influenza, hepatitis, and HIV and fulminant bacterial infectious such as typhoid and miliary tuberculosis are examples of neutropenic fevers. Auto-immune syndromes including SLE and Felty's as well as hypersensitivity and anaphylaxis to drugs and other agents may also cause neutropenia.

A benign familial form of neutropenia and an unexplained cyclic neutropenia have also been described. Finally neutropenia may be part of a pancytopenia due to marrow failure or splenomegaly with sequestration of cells in the spleen.

Clinical features of neutropenia
Severe neutropenia is particularly associated with infections of the mouth, throat and anus accompanied by painful and intractable ulcers. This is referred to as agranulocytic angina. Commensal organisms in the mouth are often responsible and septicemia is a frequent and life threatening danger.

The bone marrow should be examined. Characteristically the marrow contains many precursor myeloid cell but few mature elements. This denotes a hopeful prognosis. Few or absent precursors might indicate a more intractable aplasia or hypoplasia. Sometimes evidence of leukemia or other infiltration may be found.
 
Monocytes
Much less common than neutrophilia is a rise in the blood monocyte count above 0.8 x 109/liter. This may be found with some chronic bacterial infections including TB, brucellosis, bacterial endocarditis and typhoid. It may also occur in protozoan infections (malaria), Hodgkin disease, myelodysplasia, monocytic leukemia and treatment with GM-CSF or M-CSF.

Lymphocytes
The normal lymphocyte count in adults is from 1.2 x 109 to 4.0 x 10⁹/liter. Children have higher counts.

Many viral infectious including infectious mononucleosis, rubella, mumps, infectious hepatitis, cytomegalovirus, HIV, herpes simplex or zoster and many others cause a lymphocytosis. Some chronic infections including TB, toxoplasma, brucella and syphilis cause lymphocytosis. Acute pertussis in children although a bacterial infection can also cause a high lymphocytosis.

Other causes are thyrotoxicosis, lymphocytic leukemias, some non Hodgkin's lymphomas and hairy cell leukemia.Lymphopenia may occur with corticosteroid and other immuno-suppressive therapies, post irradiation and in immune deficiency syndromes the most important of which is AIDS.

Infectious Mononucleosis (I.M.)
This is a disease of young adults characterized by fever, sore throat, lymphadenopathy and atypical lymphocytes in the blood. Splenomegaly, skin rash and mild jaundice occur in some patients. The atypical lymphocytes are T cells reacting against B cells infected with Epstein-Barr virus (EBV). Antibodies to EB virus are present in the serum. These are heterophile antibodies which react against sheep red cells and formalinized horse red cells and can be detected by the monospot slide screening test. Laboratory diagnosis depends upon the presence of atypical lymphocytes in the blood and a positive monospot test. A high titer of EBV antibody is also present in the first 2-3 weeks. Auto-immune hemolytic anemia and/or thrombocytopenia and false positive tests for syphilis or rheumatoid arthritis and positive antinuclear factor antibodies develop in occasional cases. Most cases resolve in 4-6 weeks but rarely a chronic fatigue syndrome may persist for a longer period.

Similar clinical and hematological features can be found in CMV infection, toxoplasmosis, influenza, rubella, infectious hepatitis, agranulocytosis and initial infection with HIV. Infective lymphocytosis is a rare childhood febrile illness which can also be confused with I.M. Serological tests will usually resolve the differential diagnosis.
 
Erythrocyte Sedimentation Rate (ESR)
This test measures the speed of sedimentation of red cells in plasma over a period of 1 hour. The rate of fall is accelerated when the plasma concentration of fibrinogen and globulins is increased due to the acute phase response to many diseases. The high plasma protein level causes red cells to lose part of their negative charge and therefore stack together like a pile of coins. This is called rouleaux formation. Stacks of cells form larger particles than single cells and consequently sediment more rapidly. In normal blood the ESR is 1-5 mm/hr in men and 5-15 mm/hr in women due to their lower hematocrit. The ESR is raised in many inflammatory, neoplastic and connective tissue diseases. Particularly high values are found in chronic infections including TB, leishmaniasis, myeloma, macroglobulinemia and disseminated cancer. In general a raised ESR favors organic rather than psychosomatic disease, bacterial rather than viral infection, and malignant rather than benign tumors. The ESR can be used to monitor response to therapy. Pregnancy and many anemias cause a mild to moderate elevation. Reduced sedimentation is seen in polycythemia and in sickle cell disease. The ESR is an imprecise test but is still widely used despite limited clinical utility. An alternative and probably a more accurate, rapid and simple test for the same plasma protein changes detected by the ESR is the Plasma Viscosity. This test is not affected by anemia and is at least as sensitive and specific as the ESR. Increased plasma viscosity has the same significance as increased ESR. Low plasma viscosity values indicate low protein levels and can be used to screen for poor nutrition. Normal values are usually from 1.50-1.70 m Pa/second.