Plasma is the clear yellow fluid in which proteins (e.g., albumins, globulins, fibrinogen) are
the major solutes. Plasma proteins maintain intravascular volume, contribute to coagulation,
and are important in acid-base balance. During the second trimester, blood is formed
primarily in the fetal liver, spleen, and lymph nodes. In the last half of gestation,
hematopoiesis shifts from the fetal liver and spleen to the bone marrow.
The youngest circulating RBCs are the reticulocytes (i.e., blast forms are typically seen only
in the bone marrow. A mature RBC survives about 120 days before it is destroyed through
phagocytosis in the spleen, liver, or bone marrow. The reticulocyte count is about 4% to 6%
for the first 3 days of life, Hgb is the oxygen-carrying protein molecule in the RBC.
Hemoglobin electrophoresis, which separates each Hgb out on a gel medium, is the
diagnostic test used to differentiate the Hgb variants from Hgb A
In the full-term newborn, Hgb levels are typically high (≥14 g/dL) as a result of increased
tissue oxygenation and reduced production of erythropoietin.
The primary function of WBCs is to protect the body from invasion by foreign organisms
(e.g., viruses, bacteria, parasites, and fungi) and to distribute antibodies and other immune
response components. When the WBC count reaches a critically low level, the individual is at
risk for infection. Whereas an elevated WBC count typically indicates that an infection or
serious disease, such as leukemia, exists.
The major function of neutrophils is the phagocytosis or destruction of harmful particles and
cells, particularly bacterial organisms. A relative increase in the number of circulating
immature neutrophils (bands) is referred to as a “left shift” and typically signifies the
presence of an acute bacterial infection or inflammatory process.
A decrease in basophils (basopenia) can occur with acute allergic reactions and
hyperthyroidism as well as stress, ovulation, and pregnancy. An increase in basophils
(basophilia) can occur with allergic rhinitis/seasonal pollenosis, nephrosis, ulcerative colitis,
and hypothyroidism.
An elevation in eosinophils (eosinophilia) can occur in allergic reactions, atopic dermatitis,
asthma, and autoimmune disorders as well as parasitic infections and malignancies. A
decrease in eosinophils (eosinopenia) may occur with increased adrenosteroid production.
Lymphocytes that remain in the bone marrow (B cells) are precursors that can recognize
antigens and transform into plasma cells.
Monocytes- Their primary function is the phagocytosis of bacteria and cellular debris; they
serve as a backup system to the granulocytes, which are the body’s first line of defense.
The smallest cellular components in blood are the platelets, or thrombocytes, which are
essential to hemostasis and clot formation.
Anemia is a reduction in circulating RBCs. It can occur due to a decrease in RBC production,
abnormalities of the RBCs, a shortened RBC life span, RBC destruction, or an acute/ongoing
loss from bleeding. Common causes of microcytic (↓MCV), hypochromic (↓MCH) anemia are
iron deficiency, lead poisoning, and thalassemia trait, whereas common causes of
macrocytic (↑MCV) anemia include exposure to certain medications (e.g., anticonvulsants),
deficiencies in vitamin B12 or folate, liver disease, and hypothyroidism.
The reticulocyte count helps to distinguish disorders resulting from hemolysis (↑retic; rapid
destruction) or bleeding (loss of RBCs) from disorders resulting in the inability to produce
RBCs (↓retic), as in bone marrow depression.
Hypoproliferative anemias result from a failure in RBC production and tend to be normocytic,
normochromic anemias with a decreased reticulocyte count. Maturational anemias reflect a
defect in nuclear maturation, typically cause by nutritional deficiencies or a chemical/toxic
, exposure. The third category, hemolytic anemias, refers to anemias that result from
increased cell destruction.
Iron deficiency anemia is not only the most common pediatric hematologic disorder, but it is
also the most frequent cause of anemia in childhood. Iron deficiency anemia (IDA) is the
most common nutritional disorder and hematologic condition in the world. Dietary iron is
primarily absorbed in the duodenum. Malabsorption of iron occurs in diseases that affect this
segment of the intestine, such as celiac disease, Crohn disease, giardiasis, or resection of
the proximal small intestine. Lead poisoning (plumbism) is often a comorbid condition to IDA.
A child at risk for lead exposure should be screened at 9 to 12 months of age and again at
24 months. Whole cow’s milk should be avoided in infants younger than 12 months of age
due to its low iron content and the possibility of insensible GI blood loss. After 12 months of
age, cow’s milk ingestion should be limited to 24 oz/day.
Thalassemias are categorized into two types: alpha (α) and beta (β), based on the affected
chain. In the carrier of α thalassemia (minor/trait), only one α chain is present, which
enables the production of adequate amounts of Hgb with few or no symptoms; In the carrier
of β thalassemia (minor/trait), there are sufficient β chains to bind with the abundant α
chains and create functional Hgb molecules; however, a resultant asymptomatic mild
microcytic anemia is present. Three gene deletions result in severe, even fatal,
manifestations of disease. Two gene deletions present with hypochromia; the absence of
gene deletions causes mild anemia and often erythrocytosis. A single globin gene deletion is
clinically insignificant. B-thalassemia minor: The primary diagnostic feature is increased Hgb
A2 (>3.5%) on electrophoresis. Homozygous β thalassemia major (or Cooley anemia) is
associated with severe anemia resulting from the decreased or absent production of Hgb A.
Affected infants usually become symptomatic in the first year of life and have pallor, failure
to thrive, hepatosplenomegaly, and a severe anemia with an average Hgb of 6 g/dL and low
MCV (60 to 70 fL).
RBC transfusions are usually necessary every 2 to 4 weeks with the goal of maintaining a
pretransfusion Hgb level between 9.5 and 10.5 g/dL. Iron chelation is necessary to treat the
hyperferric state produced by repeated transfusions and prevent complications primarily of
the heart, liver, and endocrine system. Deferasirox is an oral agent taken once daily at 20 to
30 mg/kg/day; it stabilizes the ferritin levels, thus achieving a negative iron balance.
Macrocytic (megaloblastic) anemias are characterized by macrocytic RBCs, hypersegmented
polymorphonuclear leukocytes (PMNs) in the peripheral blood, and megaloblasts in the bone
marrow. Relatively rare, macrocytic anemias are primarily due to a lack of folic acid, vitamin
B12, or both.
Hemolytic anemias are caused by premature destruction of RBCs and increased marrow
production of reticulocytes. Invasive bacterial infection is the leading cause of death in
young children with Sickle Cell Anemia. The treatment of choice for children with severe HS
requiring multiple transfusions is splenectomy, which usually produces a clinical cure. It
should be deferred until after 6 years of age because of the increased risk of encapsulated
bacterial infection before that age. Risks associated with splenectomy are postsplenectomy
sepsis, penicillin-resistant pneumococcal infection, pulmonary hypertension, and ischemic
heart disease and stroke. Pneumococcal and meningococcal vaccines should be given before
splenectomy.
If the PT and aPTT are elevated in association with thrombocytopenia, the probable
diagnosis is disseminated intravascular coagulation (DIC), which is a syndrome secondary to
an underlying disorder such as sepsis, malignancy, toxins, or liver failure. Immune or ITP is
the most common of the thrombocytopenic purpuras in childhood and is believed to be an
autoimmune response in which circulating platelets are destroyed. It usually occurs after
viral illnesses. In a sick, febrile child with isolated thrombocytopenia, petechiae, or purpura,
the major diagnosis to consider first is meningococcemia.