Erythrocyte Disorders

Dr. Sangeeta Gourh

Introduction

  • Erythrocytes, commonly called red blood cells (RBCs), are specialized blood cells responsible mainly for transporting oxygen from the lungs to tissues and carrying carbon dioxide back to the lungs.
  • Normal erythrocytes are biconcave, anucleate cells containing hemoglobin.
  • They have a typical lifespan of approximately 120 days and are continuously produced in the bone marrow through a process called erythropoiesis.
  • Disorders of erythrocytes can affect their number, size, shape, hemoglobin content, or lifespan.
  • These abnormalities may result in anemia, hemolysis, abnormal hemoglobin production, or other hematological conditions.
  • Laboratory investigations are essential for identifying the type and cause of an erythrocyte disorder.

Classification of Erythrocyte Disorders

Erythrocyte disorders can broadly be classified into:

1. Disorders of RBC Production

These occur when the bone marrow does not produce adequate or normal RBCs.

Examples:

  • Iron deficiency anemia
  • Vitamin B12 deficiency anemia
  • Folate deficiency anemia
  • Aplastic anemia
  • Anemia of chronic disease

2. Disorders of Hemoglobin

These occur due to abnormalities in the structure or production of hemoglobin.

Examples:

  • Sickle cell disease
  • Thalassemia
  • Hemoglobin C disease
  • Other hemoglobinopathies

3. Hemolytic Disorders

These occur when RBCs are destroyed prematurely.

Examples:

  • Hereditary spherocytosis
  • G6PD deficiency
  • Autoimmune hemolytic anemia
  • Sickle cell disease

4. Disorders of RBC Shape

These are characterized by abnormal RBC morphology.

Examples:

  • Spherocytosis
  • Elliptocytosis
  • Sickle cells
  • Target cells
  • Schistocytes

5. Disorders of RBC Size

RBCs may become smaller or larger than normal.

  • Microcytosis: Small RBCs
  • Macrocytosis: Large RBCs
  • Normocytosis: Normal-sized RBCs

Common Erythrocyte Disorders

1. Iron Deficiency Anemia

  • Iron deficiency anemia is one of the most common causes of anemia.
  • Iron is essential for hemoglobin synthesis. When iron is insufficient, hemoglobin production decreases.

Laboratory findings

  • Decreased hemoglobin
  • Decreased hematocrit
  • Decreased MCV
  • Decreased MCH
  • Decreased serum ferritin
  • Decreased serum iron
  • Increased total iron-binding capacity (TIBC)
  • Increased transferrin
  • Peripheral smear shows microcytic hypochromic RBCs

2. Megaloblastic Anemia

  • Megaloblastic anemia occurs mainly due to deficiency of vitamin B12 or folate.
  • These vitamins are important for DNA synthesis. Their deficiency causes abnormal maturation of RBC precursors in the bone marrow.

Laboratory findings

  • Decreased hemoglobin
  • Increased MCV
  • Macrocytes on peripheral smear
  • Oval macrocytes
  • Hypersegmented neutrophils
  • Increased LDH
  • Increased indirect bilirubin

Vitamin B12 deficiency

Laboratory evaluation may include:

  • Serum vitamin B12
  • Methylmalonic acid
  • Homocysteine

Folate deficiency

Laboratory evaluation may include:

  • Serum folate
  • Red cell folate
  • Homocysteine

3. Thalassemia

  • Thalassemia is an inherited disorder characterized by reduced synthesis of one or more globin chains of hemoglobin.

The major types are:

  • Alpha thalassemia
  • Beta thalassemia

Laboratory findings

  • Decreased hemoglobin
  • Decreased MCV
  • Decreased MCH
  • Microcytosis
  • Hypochromia
  • Target cells on peripheral smear
  • Increased RBC count may be seen in some thalassemia traits

Important tests

  • CBC
  • Peripheral blood smear
  • Hemoglobin analysis
  • Hemoglobin electrophoresis or HPLC
  • Genetic testing when required

In beta-thalassemia trait, HbA2 is commonly increased.

4. Sickle Cell Disease

  • Sickle cell disease is an inherited hemoglobin disorder caused by a mutation affecting the β-globin gene.
  • The abnormal hemoglobin is called HbS.
  • Under certain conditions, deoxygenated HbS can polymerize, causing RBCs to become rigid and sickle-shaped.

Laboratory diagnosis

Important investigations include:

  • CBC
  • Peripheral blood smear
  • Sickling/solubility screening tests
  • Hemoglobin electrophoresis
  • HPLC
  • Molecular genetic testing when indicated

Peripheral smear may show

  • Sickle-shaped RBCs
  • Target cells
  • Polychromasia
  • Nucleated RBCs in some patients

Hemoglobin analysis is important for identifying HbS and distinguishing different sickling disorders.

5. Hereditary Spherocytosis

  • Hereditary spherocytosis is an inherited RBC membrane disorder.
  • The RBCs become spherical instead of biconcave and are more easily destroyed, particularly in the spleen.

Laboratory findings

  • Anemia of variable severity
  • Increased reticulocyte count
  • Increased MCHC may occur
  • Spherocytes on peripheral smear
  • Increased indirect bilirubin
  • Increased LDH
  • Decreased haptoglobin

Specialized tests

  • Eosin-5-maleimide (EMA) binding test
  • Osmotic fragility testing

The EMA binding test is commonly used in modern laboratory evaluation.

6. Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

  • G6PD is an important enzyme in the pentose phosphate pathway.
  • It helps RBCs maintain adequate reduced glutathione and protect themselves against oxidative damage.
  • G6PD deficiency can cause hemolysis after exposure to certain oxidative stresses.

These may include:

  • Certain drugs
  • Infections
  • Fava bean exposure

Laboratory findings during hemolysis

  • Increased reticulocyte count
  • Increased indirect bilirubin
  • Increased LDH
  • Decreased haptoglobin
  • Hemoglobinuria may occur

Peripheral smear

May show:

  • Bite cells
  • Blister cells
  • Polychromasia

Confirmatory test

  • Quantitative G6PD enzyme activity assay is used for diagnosis.
  • Testing during or shortly after a hemolytic episode can sometimes be misleading because young RBCs and reticulocytes have relatively higher G6PD activity.

7. Autoimmune Hemolytic Anemia

  • Autoimmune hemolytic anemia occurs when antibodies react against the patient’s own RBCs.

The major categories include:

  • Warm autoimmune hemolytic anemia
  • Cold antibody-mediated hemolytic anemia

Laboratory findings

Evidence of hemolysis may include:

  • Increased reticulocyte count
  • Increased indirect bilirubin
  • Increased LDH
  • Decreased haptoglobin

Important diagnostic test

  • Direct antiglobulin test (DAT) is an important laboratory investigation.
  • It detects immunoglobulin and/or complement associated with the patient’s RBCs.

Laboratory Diagnosis 

The laboratory diagnosis usually begins with basic hematological investigations and progresses to specialized tests depending on the findings.

1. Complete Blood Count

The CBC is one of the most important initial investigations.

It provides information about:

  • Hemoglobin
  • Hematocrit
  • RBC count
  • MCV
  • MCH
  • MCHC
  • RDW

Important RBC indices

  • MCV: Indicates the average size of RBCs.
  • MCH: Indicates the average amount of hemoglobin per RBC.
  • MCHC: Indicates the average concentration of hemoglobin within RBCs.
  • RDW: Indicates variation in RBC size.

2. Peripheral Blood Smear

  • A peripheral blood smear allows direct examination of RBC morphology under a microscope.
  • It can provide important clues regarding the underlying disorder.
  • Common RBC morphological abnormalities
RBC finding Possible association
Microcytes Iron deficiency, thalassemia
Macro-ovalocytes Vitamin B12/folate deficiency
Spherocytes Hereditary spherocytosis, autoimmune hemolysis
Sickle cells Sickle cell disease
Target cells Thalassemia, hemoglobinopathies, liver disease
Schistocytes Microangiopathic hemolysis
Bite cells Oxidative hemolysis, including G6PD deficiency
Teardrop cells Marrow infiltration and other disorders
Polychromasia Increased reticulocytes

3. Reticulocyte Count

  • Reticulocytes are immature RBCs released from the bone marrow.
  • The reticulocyte count helps assess the bone marrow response to anemia.
  • Increased reticulocyte count

May occur in:

  • Hemolytic anemia
  • Recent blood loss
  • Response to treatment of some nutritional anemias

Decreased or inadequately increased reticulocyte count

May occur when RBC production is impaired, such as in:

  • Iron deficiency
  • Vitamin B12 deficiency
  • Folate deficiency
  • Bone marrow failure

4. Iron Profile

  • Iron studies are useful when microcytic anemia is suspected.

Important parameters include:

  • Serum ferritin
  • Serum iron
  • TIBC
  • Transferrin saturation

Typical pattern in iron deficiency

↓ Ferritin + ↓ serum iron + ↑ TIBC

However, ferritin is also an acute-phase reactant and may increase during inflammation.

5. Vitamin B12 and Folate Testing

  • These investigations are useful in patients with macrocytic anemia.

Tests may include:

  • Serum vitamin B12
  • Serum folate
  • Methylmalonic acid
  • Homocysteine

Biochemical pattern

Vitamin B12 deficiency:

  • ↑ Methylmalonic acid
  • ↑ Homocysteine

Folate deficiency:

  • Normal methylmalonic acid
  • ↑ Homocysteine

6. Hemoglobin Electrophoresis

Hemoglobin electrophoresis separates different types of hemoglobin based on their physical properties.

It can help identify:

  • HbA
  • HbA2
  • HbF
  • HbS
  • HbC
  • Other hemoglobin variants

It is an important investigation for suspected hemoglobinopathies.

7. High-Performance Liquid Chromatography

  • HPLC is widely used for hemoglobin analysis.
  • It can help identify and quantify different hemoglobin fractions.

It is particularly useful in the evaluation of:

  • Thalassemia
  • Sickle cell disorders
  • Other hemoglobin variants

8. Hemolysis Profile

When hemolysis is suspected, laboratory investigations may include:

  • Reticulocyte count
  • Indirect bilirubin
  • LDH
  • Haptoglobin
  • Peripheral blood smear
  • Urinalysis

Typical biochemical pattern of hemolysis

↑ Reticulocytes + ↑ indirect bilirubin + ↑ LDH + ↓ haptoglobin

9. Direct Antiglobulin Test

  • The Direct Antiglobulin Test (DAT) detects antibodies or complement attached to the patient’s RBCs.

It is particularly useful in the evaluation of:

  • Autoimmune hemolytic anemia
  • Hemolytic disease of the newborn
  • Hemolytic transfusion reactions

10. Enzyme Assays

  • Specific RBC enzyme assays may be performed when an inherited enzyme defect is suspected.

Examples include:

  • G6PD activity assay
  • Pyruvate kinase activity assay

These tests help identify RBC enzyme disorders.

11. Bone Marrow Examination

  • Bone marrow examination is not required for every erythrocyte disorder.

It may be considered when:

  • The cause of anemia remains unexplained.
  • Bone marrow disease is suspected.
  • There are abnormalities in multiple blood cell lines.
  • A production disorder needs further evaluation.

Bone marrow examination can provide information about:

  • Erythroid precursors
  • Megaloblastic changes
  • Iron stores
  • Marrow infiltration
  • Other hematological abnormalities

12. Molecular and Genetic Testing

  • Genetic testing can be useful for diagnosing inherited RBC disorders.

It may be considered for:

  • Thalassemia
  • Sickle cell disease
  • G6PD deficiency in selected situations
  • Hereditary RBC membrane disorders
  • Other rare hemoglobinopathies

Laboratory Approach to an Anemic Patient

A simple approach is:

Anemia detected on CBC

↓

Check MCV

↓ MCV — Microcytic anemia

Consider:

  • Iron deficiency
  • Thalassemia
  • Anemia of chronic disease
  • Other causes

Investigations: Iron profile, peripheral smear, hemoglobin analysis.

Normal MCV — Normocytic anemia

Consider:

  • Acute blood loss
  • Hemolysis
  • Chronic disease
  • Bone marrow disorders

Investigations: Reticulocyte count, hemolysis profile, peripheral smear and other tests as indicated.

↑ MCV — Macrocytic anemia

Consider:

  • Vitamin B12 deficiency
  • Folate deficiency
  • Liver disease
  • Alcohol-related causes
  • Drug effects
  • Other causes

Investigations: Vitamin B12, folate, peripheral smear and additional testing as appropriate.