Classification and Diagnosis of Anemia in Children

Abstract

Anemia can be defined as a reduction in hemoglobin concentration, hematocrit, or number of red blood cells per cubic millimeter. The lower limit of the normal range is set at two standard deviations below the mean for age and sex for the normal population. Causes of anemia are classified based on morphology, mean corpuscular volume (MCV) and red cell distribution width (RDW)

Keywords

Anemia, Classification, Red cell morphology, Mean corpuscular volume (MCV), Red cell distribution width (RDW), Hemolytic anemia, diagnosis

Classification and Diagnosis

1 Children with cyanotic congenital heart disease, chronic respiratory insufficiency, arteriovenous pulmonary shunts, or hemoglobinopathies that alter oxygen affinity can be functionally anemic with hemoglobin levels in the normal range.

This definition will result in 2.5% of the normal population being classified as anemic and by definition 2.5% of the population may receive unnecessary hematological investigations. Clinicians should be cognizant of this and temper investigations of the patient in the light of other clinical and laboratory findings.

The first step in diagnosis of anemia is to establish whether the abnormality is isolated to a single cell line (red blood cells only) or whether it is part of a multiple cell line abnormality (red cells, white cells, and platelets). Abnormalities of two- or three-cell lines usually indicate one of the following:

•

bone marrow involvement (e.g., aplastic anemia, leukemia), or
•

an immunologic disorder (e.g., connective tissue disease or immunoneutropenia, idiopathic thrombocytopenic purpura (ITP), or immune hemolytic anemia singly or in combination), or
•

sequestration of cells (e.g., hypersplenism).

Table 3.1 presents an etiologic classification of anemia and the diagnostic features in each case.

Table 3.1

Etiologic Classification and Major Diagnostic Features of Anemia in Children

Etiologic classification	Diagnostic features
1. Impaired red cell formation a. Deficiency i. Decreased dietary intake (e.g., excessive cows’ milk (iron-deficiency anemia), vegan (vitamin B ₁₂deficiency)) ii. Increased demand, for example, growth (iron) hemolysis (folic acid) iii. Decreased absorption • Specific: intrinsic factor lack (vitamin B ₁₂) • Generalized: malabsorption syndrome (e.g., folic acid, iron) iv. Impairment in red cell formation can result from one of the following deficiencies:
i. Iron deficiency	Hypochromic, microcytic red cells; low MCV, low MCH, low MCHC, high RDW, ^alow serum ferritin, high FEP, guaiac positivity
ii. Folate deficiency	Macrocytic red cells, high MCV, high RDW, megaloblastic marrow, low serum, and red cell folate
iii. Vitamin B ₁₂deficiency	Macrocytic red cells, high MCV, high RDW, megaloblastic marrow, low serum B ₁₂, decreased gastric acidity; Schilling test positive
iv. Vitamin C deficiency	Clinical scurvy
v. Protein deficiency	Kwashiorkor
vi. Vitamin B ₆deficiency	Hypochromic red cells, sideroblastic bone marrow, high serum ferritin
vii. Thyroxine deficiency	Clinical hypothyroidism, low T ₄, high TSH
b. Bone marrow failure i. Failure of a single cell line • Megakaryocytes ^b
Amegakaryocytic thrombocytopenic purpura with absent radii (TAR)	Limb abnormalities, thrombocytopenic purpura absent megakaryocytes
• Red cell precursors
Congenital red cell aplasia (Diamond–Blackfan anemia)	Absent red cell precursors
Acquired red cell aplasia (transient erythroblastopenia of childhood, TEC)	Absent red cell precursors
• White cell precursors ^b
Congenital neutropenias	Neutropenia, recurrent infection
ii. Failure of all cell lines (characterized by pancytopenia and acellular or hypocellular marrow) • Congenital
Fanconi anemia	Multiple congenital anomalies, chromosomal breakage
Familial without anomalies	Familial history, no congenital anomalies
Dyskeratosis congenita	Marked mucosal and cutaneous abnormalities
• Acquired
Idiopathic	No identifiable cause
Secondary	History of exposure to drugs, radiation, household toxins, infections; (parvovirus B19, HIV) associated immunologic disease
iii. Infiltration
• Benign (e.g., osteopetrosis, storage diseases)
• Malignant primary (e.g., leukemia, myelofibrosis)	Bone marrow: morphology, cytochemistry, immunologic markers, cytogenetics, molecular features
• Secondary (e.g., neuroblastoma, lymphoma)	VMA, imaging studies, skeletal survey, bone marrow
iv. Dyshematopoietic anemias (decreased erythropoiesis, decreased iron utilization)
• Anemia of chronic disease	Evidence of systemic illness
• Renal failure and hepatic disease	BUN and liver function tests
• Disseminated malignancy	Clinical evidence
• Connective tissue diseases	Rheumatoid arthritis
• Malnutrition	Clinical evidence
• Sideroblastic anemias	Hypochromic anemia, ring sideroblasts
	Overt or occult guaiac positive
1. Blood loss 2. Hemolytic anemia
a. Corpuscular	Splenomegaly, jaundice
i. Membrane defects (spherocytosis, elliptocytosis)	Morphology, osmotic fragility
ii. Enzymatic defects (pyruvate kinase, G6PD)	Autohemolysis, enzyme assays
iii. Hemoglobin defects
• Heme
• Globin
Qualitative (e.g., sickle cell)	Hb electrophoresis
Quantitative (e.g., thalassemia)	Quantitative HbF, A ₂content
b. Extracorpuscular
i. Immune	Direct antiglobulin test (Coombs’ test)
• Isoimmune • Autoimmune
Idiopathic	Direct antiglobulin test, antibody identification
Secondary
Immunologic disorder (e.g., lupus)	Decreased C ₃, C ₄, CH ₅₀-positive ANA
One-cell line (e.g., red cells)	Anemia—direct antiglobulin test positive
Multiple cell line (e.g., white blood cells, platelets)	Neutropenia—immunotropenia, thrombocytopenia—ITP
ii. Nonimmune (idiopathic, secondary)

FEP, free erythrocyte protoporphyrin; G6PD, glucose-6-phosphate dehydrogenase; Hb, hemoglobin; ITP, idiopathic thrombocytopenic purpura, MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration; MCV, mean corpuscular volume; RBC, red blood cell; RDW, red cell distribution width (see definition); VMA, vanillylmandelic acid.

a RDW 5 coefficient of variation of the RBC distribution width (normal between 11.5% and 14.5%).

b Not associated with anemia.

Once the anemia has been established to be exclusively a red cell problem a useful approach to understanding the anemia is to separate it into two pathogenetic categories

1.

Disorders of depressed red cell formation due to ineffectual erythropoeisis in which the marrow has many erythroblasts and there is a reticulocytosis or failure of erythropoiesis in which there is a paucity of erythroblasts in the marrow, an absolute erythroblastopenia and there is a reticulocytopenia (usually due to marrow failure diseases).
2.

Disorders of erythrocyte destruction (hemolysis) or red cell loss (hemorrhage).

The blood smear is very helpful in the diagnosis of anemia. It establishes whether the anemia is hypochromic, microcytic, normocytic, macrocytic, or shows specific morphologic abnormalities suggestive of red cell membrane disorders (e.g., spherocytes, stomatocytosis, or elliptocytosis) or hemoglobinopathies (e.g., sickle cell disease, thalassemia). Table 3.2 lists the differential diagnoses based on the specific red cell morphological abnormalities.

Table 3.2

Specific Red Cell Morphologic Abnormalities

1.

Target cells
- Increased surface/volume ratio (generally does not affect red cell survival)
  - i.
    
    Thalassemic syndromes
  - ii.
    
    Hemoglobinopathies
    - –
      
      Hb AC or CC
    - –
      
      Hb SS, SC, S-Thal
    - –
      
      HbE (heterozygote and homozygote)
    - –
      
      HbD
  - iii.
    
    Obstructive liver disease
  - iv.
    
    Postsplenectomy or hyposplenic states
  - v.
    
    Severe iron deficiency
  - vi.
    
    LCAT deficiency: congenital disorder of lecithin/cholesterol acyltransferase deficiency (corneal opacifications, proteinuria, target cells, moderately severe anemia)
  - vii.
    
    Abetalipoproteinemia
  - viii.
    
    Hereditary xerocytosis
2.

Spherocytes
- Decreased surface/volume ratio, hyperdense (>MCHC)
  - i.
    
    Hereditary spherocytosis
  - ii.
    
    ABO incompatibility: antibody-coated fragment of RBC membrane removed
  - iii.
    
    Autoimmune hemolytic anemia: antibody-coated fragment of RBC membrane removed
  - iv.
    
    G6PD deficiency
  - v.
    
    Microangiopathic hemolytic anemia (MAHA): fragment of RBC lost after impact with abnormal surface
  - vi.
    
    SS disease: fragment of RBC removed in reticuloendothelial system
  - vii.
    
    Hypersplenism
  - viii.
    
    Burns: fragment of damaged RBC removed by spleen
  - ix.
    
    Posttransfusion
  - x.
    
    Pyruvate kinase deficiency
  - xi.
    
    Water-dilution hemolysis: fragment of damaged RBC removed by spleen
3.

Acanthocytes (spur cells) ^a
- Cells with 5–10 spicules of varying length; spicules irregular in space and thickness, with wide bases; appear smaller than normal cells because they assume a spheroid shape
  - i.
    
    Liver disease
  - ii.
    
    Disseminated intravascular coagulation (and other MAHA)
  - iii.
    
    Postsplenectomy or hyposplenic state
  - iv.
    
    Vitamin E deficiency
  - v.
    
    Hypothyroidism
  - vi.
    
    Abetalipoproteinemia: rare congenital disorder; 50–100% of cells acanthocytes; associated abnormalities (fat malabsorption, retinitis pigmentosa, neurologic abnormalities)
  - vii.
    
    Malabsorptive states
4.

Echinocytes (burr cells) ^a
- 10–30 spicules equal in size and evenly distributed over RBC surface; caused by alteration in extracellular or intracellular environment
  - i.
    
    Artifact
  - ii.
    
    Renal failure
  - iii.
    
    Dehydration
  - iv.
    
    Liver disease
  - v.
    
    Pyruvate kinase deficiency
  - vi.
    
    Peptic ulcer disease or gastric carcinoma
  - vii.
    
    Immediately after red cell transfusion
  - viii.
    
    Rare congenital anemias due to decreased intracellular potassium
5.

Pyknocytes ^a
- Distorted, hyperchromic, contracted RBC; can be similar to echinocytes and acanthocytes
6.

Schistocytes
- Helmet, triangular shapes, or small fragments. Caused by fragmentation upon impact with abnormal vascular surface (e.g., fibrin strand, vasculitis, artificial surface in circulation)
  - i.
    
    Disseminated intravascular coagulation (DIC)
  - ii.
    
    Severe hemolytic anemia (e.g., G6PD deficiency)
  - iii.
    
    MAHA
  - iv.
    
    Hemolytic uremic syndrome
  - v.
    
    Prosthetic cardiac valve, abnormal cardiac valve, cardiac patch, coarctation of the aorta
  - vi.
    
    Connective tissue disorder (e.g., SLE)
  - vii.
    
    Kasabach–Merritt syndrome
  - viii.
    
    Purpura fulminans
  - ix.
    
    Renal vein thrombosis
  - x.
    
    Burns (spheroschistocytes as a result of heat)
  - xi.
    
    Thrombotic thrombocytopenia purpura
  - xii.
    
    Homograft rejection
  - xiii.
    
    Uremia, acute tubular necrosis, glomerulonephritis
  - xiv.
    
    Malignant hypertension
  - xv.
    
    Systemic amyloidosis
  - xvi.
    
    Liver cirrhosis
  - xvii.
    
    Disseminated carcinomatosis
  - xviii.
    
    Chronic relapsing schistocytic hemolytic anemia
7.

Elliptocytes
- Elliptical cells, normochromic; seen normally in less than 1% of RBCs; larger numbers occasionally seen in a normal patient
  - i.
    
    Hereditary elliptocytosis
  - ii.
    
    Iron deficiency (increased with severity, hypochromic)
  - iii.
    
    SS disease
  - iv.
    
    Thalassemia major
  - v.
    
    Severe bacterial infection
  - vi.
    
    SA trait
  - vii.
    
    Leukoerythroblastic reaction
  - viii.
    
    Megaloblastic anemias
  - ix.
    
    Any anemia may occasionally present with up to 10% elliptocytes
  - x.
    
    Malaria
8.

Teardrop cells
- Shape of drop, usually microcytic, often also hypochromic
  - i.
    
    Newborn
  - ii.
    
    Thalassemia major
  - iii.
    
    Leukoerythroblastic reaction
  - iv.
    
    Myeloproliferative syndromes
9.

Stomatocytes
- Has a slit-like area of central pallor
  - i.
    
    Normal (in small numbers)
  - ii.
    
    Hereditary stomatocytosis
  - iii.
    
    Artifact
  - iv.
    
    Thalassemia
  - v.
    
    Acute alcoholism
  - vi.
    
    Rh null disease (absence of Rh complex)
  - vii.
    
    Liver disease
  - viii.
    
    Malignancies
10.

Nucleated red blood cells
- Not normal in the peripheral blood beyond the first week of life
  - i.
    
    Newborn (first 3–4 days)
  - ii.
    
    Intense bone marrow stimulation
    - –
      
      Hypoxia (especially postcardiac arrest)
    - –
      
      Acute bleeding
    - –
      
      Severe hemolytic anemia (e.g., thalassemia, SS hemoglobinopathy)
  - iii.
    
    Congenital infections (e.g., sepsis, congenital syphilis, CMV, rubella)
  - iv.
    
    Postsplenectomy or hyposplenic states: spleen normally removes nucleated RBC
  - v.
    
    Leukoerythroblastic reaction: seen with extramedullary hematopoiesis and bone marrow replacement; most commonly leukemia or solid tumor—fungal and mycobacterial infection may also do this; leukoerythroblastic reaction is also associated with teardrop red cells, 10,000–20,000 WBC with small to moderate numbers of metamyelocytes, myelocytes, and promyelocytes; thrombocytosis with large bizarre platelets
  - vi.
    
    Megaloblastic anemia
  - vii.
    
    Dyserythropoietic anemias
11.

Blister cells
- i.
  
  Red cell area under membrane, free of hemoglobin, appearing like a blister
- ii.
  
  G6PD deficiency (during hemolytic episode)
- iii.
  
  SS disease
- iv.
  
  Pulmonary emboli
12.

Basophilic stippling
- Coarse or fine punctate basophilic inclusions that represent aggregates of ribosomal RNA
  - i.
    
    Hemolytic anemias (e.g., thalassemia trait)
  - ii.
    
    Iron-deficiency anemia
  - iii.
    
    Lead poisoning
13.

Howell–Jolly bodies
- Small, well-defined, round, densely stained nuclear-remnant inclusions; 1 mm in diameter; centric in location
  - i.
    
    Postsplenectomy or hyposplenia
  - ii.
    
    Newborn
  - iii.
    
    Megaloblastic anemias
  - iv.
    
    Dyserythropoietic anemias
  - v.
    
    A variety of types of anemias (rarely iron-deficiency anemia, hereditary spherocytosis)
14.

Cabot’s Ring bodies
- Nuclear remnant ring configuration inclusions
  - i.
    
    Pernicious anemia
  - ii.
    
    Lead toxicity
15.

Heinz bodies
- Denatured aggregated hemoglobin
  - i.
    
    Normal in newborn
  - ii.
    
    Thalassemia
  - iii.
    
    Asplenia
  - iv.
    
    Chronic liver disease
  - v.
    
    Heinz body hemolytic anemia