Overview
Hemolytic anemia due to abnormal hemoglobin synthesis arises from two main mechanisms: thalassemia, a quantitative defect in the synthesis of one or more globin chains, and hemoglobinopathies, qualitative structural defects in the globin chain caused by amino acid substitutions, deletions or additions.
These are among the most common inherited blood disorders worldwide, with a significant prevalence in the Indian population, particularly beta thalassemia and sickle cell hemoglobin (HbS). Accurate laboratory diagnosis is essential for genetic counseling and family screening to prevent the birth of severely affected children.
Learning Objectives
After this lesson you will be able toโฆ- Describe the pathogenesis and laboratory diagnosis of beta thalassemia major and minor.
- Describe the pathogenesis of hemoglobinopathies, especially sickle cell hemoglobin.
- Explain the laboratory tests used to detect and quantify HbS, HbF and other abnormal hemoglobins.
- Identify the peripheral blood smear features of thalassemia major, thalassemia minor and sickle cell anemia.
- Describe other clinically important hemoglobinopathies seen in India โ HbE, HbD and HbC.
Clinical Story
Why This MattersA 6-month-old infant from a Punjabi family is brought in with pallor, recurrent infections and an enlarged abdomen. The pediatrician suspects Cooley's anemia and orders a CBC, peripheral smear and hemoglobin electrophoresis. The lab technician's correct identification of markedly elevated HbF with target cells and nucleated RBCs on the smear becomes the deciding factor in starting lifelong transfusion therapy and offering the family genetic counseling for future pregnancies.
Core Concepts
Beta thalassemia is an autosomal recessive disorder with decreased production of beta globin chains. Heterozygotes (one normal gene, one thalassemia gene) compensate with increased HbA2 and delta chain production, producing a mild, well-compensated microcytic hypochromic anemia called beta thalassemia minor (trait). Homozygotes (two thalassemia genes) cannot produce normal HbA, causing severe chain imbalance โ beta thalassemia major, also called Cooley's anemia, which is transfusion-dependent for life. The gene is more common among Punjabis, Gujaratis, Marwaris and Sindhis in India.
Presents by 5โ6 months of age with pallor, frequent infections and hepatosplenomegaly. Ineffective erythropoiesis causes marrow expansion and skeletal deformity, and iron overload from repeated transfusions damages the heart, liver and pancreas. Hb may fall to 3โ4 g/dL, with markedly increased RDW, elevated reticulocyte count, indirect bilirubinemia, and raised LDH/ferritin. The peripheral smear shows anisocytosis, poikilocytosis, microcytosis, fragmented cells, nRBC, basophilic stippling and target cells. HPLC shows mainly HbF with normal HbA2; no HbA is detectable in severe ฮฒโฐ thalassemia. Treatment is regular transfusion (maintaining Hb 10.5โ11.0 g/dL), iron chelation, and bone marrow transplantation.
Mild, hypochromic microcytic anemia which must be differentiated from iron deficiency anemia. RBC count is increased despite mild Hb reduction. MCV/MCH decreased but MCHC normal; RDW mildly increased (14โ15%). No polychromasia on smear; reticulocyte count normal; bone marrow and iron studies normal. HPLC confirms diagnosis: raised HbA2 (3.7โ7.0%), 80โ85% HbA, and less than 1.0% HbF.
Caused by a single amino acid substitution in the beta globin chain โ glutamic acid replaced by valine at position 6 (ฮฑ2ฮฒ2โถglu-val). Under low oxygen tension the abnormal hemoglobin polymerizes and deforms red cells into a sickle shape, causing microvascular stasis, hypoxic tissue damage and hemolysis. Inherited as autosomal recessive; homozygotes (HbSS) develop sickle cell anemia while heterozygotes are asymptomatic HbS trait carriers. In India, HbS is found in tribal belts of central India, Maharashtra, Madhya Pradesh, Bihar, Orissa, West Bengal, the Western Ghats, Tamil Nadu and Kerala.
HbE is common in North Eastern India; homozygous HbE and HbE trait are usually asymptomatic but HbE/ฮฒ-thalassemia is a moderately severe hemolytic anemia. HbD is common in the Punjabi population; HbD/ฮฒ-thal produces moderately severe hemolytic anemia. HbC is found mainly in West Africa; heterozygotes are asymptomatic while homozygotes develop mild hemolytic anemia with prominent target cells.
Laboratory Principle
The sickle cell solubility test relies on the fact that deoxygenated HbS is far less soluble than HbA in a high-molarity phosphate buffer, causing turbidity and curdy precipitation. The sickling preparation demonstrates the physical deformation of red cells into sickle shapes when HbS is deoxygenated by sodium dithionite. Hemoglobin electrophoresis and HPLC separate hemoglobin variants based on differences in electrical charge and chromatographic affinity, allowing identification and quantification of HbA, HbA2, HbF, HbS and other variants.
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| Disodium hydrogen phosphate + sodium dithionite | Freshly prepared working solution | Sickle cell preparation reagent | Prepare fresh before use |
| KHโPOโ, KโHPOโ, saponin, sodium dithionite | In distilled water | Solubility test for HbS | Room temperature, prepare fresh |
| EDTA anticoagulated blood | Whole blood sample | Specimen for smear, sickling & solubility tests | 2โ8ยฐC, test within a few hours |
Step-by-Step Procedure
Make a fresh working solution of disodium hydrogen phosphate and sodium dithionite immediately before use.
Add 5 drops of the reagent to a drop of EDTA-anticoagulated blood on a clean glass slide.
Place a coverslip over the diluted blood and seal the edges with paraffin or nail polish to prevent air entry.
Examine at 40x with the condenser lowered. Sickling occurs almost immediately in sickle cell anemia and within one hour in sickle cell trait.
Perform the solubility test for HbS or quantify with HPLC. Compare against appropriately set positive and negative controls.
Flow Diagram
Quality Control
Always run known positive (HbSS) and negative (HbAA) controls alongside patient samples for sickling and solubility tests. Ensure the sickling reagent is freshly prepared, since old dithionite solutions lose reducing power and give false negatives.
Participate in external proficiency testing schemes for hemoglobinopathy screening to validate electrophoresis and HPLC calibration and interpretation accuracy.
Reference Values
Normal Rangesโ ๏ธ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| Raised HbA2 (3.7โ7.0%), low MCV/MCH, normal MCHC | Beta thalassemia minor / trait | Screen spouse; offer genetic counseling |
| HbF predominant, no/minimal HbA | Beta thalassemia major | Initiate transfusion program & chelation therapy |
| Positive sickling / solubility test | Sickle cell trait or disease (confirm with HPLC/electrophoresis) | Confirm zygosity; counsel on vaso-occlusive risk |
Common Errors & How to Avoid Them
Cause: Stale or improperly prepared dithionite reagent, or air entry under the coverslip.
Prevention: Always prepare reagent fresh and seal coverslip edges completely with paraffin or nail polish.
Cause: Recently transfused patients show a mixture of donor and patient hemoglobin on electrophoresis/HPLC.
Prevention: Note transfusion history before interpreting Hb fraction results; repeat testing after adequate washout period if possible.
Cause: Assuming a single abnormal band represents simple trait without considering combinations like HbS/ฮฒ-thal.
Prevention: Correlate smear morphology, HbA2/HbF levels and family history with electrophoresis pattern.
Laboratory Tips from the Bench
Target cells and basophilic stippling on a microcytic smear should always prompt a thalassemia screen, especially in populations with high carrier rates.
Remember that thalassemia minor has an increased RBC count despite a low Hb โ this helps distinguish it from iron deficiency anemia, where the RBC count is typically also low.
"Glu-Val at 6" โ remember sickle hemoglobin's defect: glutamic acid replaced by valine at position 6 of the beta chain.
Important Notes
Since thalassemia and hemoglobinopathies are inherited disorders, detailed family studies, DNA analysis and screening of blood relatives should be undertaken, with genetic counseling offered to prevent the birth of severely affected children.
While gel electrophoresis and the Alkali Denaturation test for HbF remain valid, HPLC is now the preferred method as it quantifies hemoglobin fractions faster and more accurately.
Interactive Quiz
Test Your KnowledgeFlashcards
Tap to flipClick or tap any card to reveal the answer.
Clinical Case Study
Apply Your KnowledgePresents with pallor since age 5 months, recurrent chest infections and a palpably enlarged spleen and liver. Parents are first cousins from a Sindhi family with no prior history of blood disorders.
The severe anemia, hepatosplenomegaly, marked RDW elevation and predominant HbF with no detectable HbA on HPLC in an infant from a high-prevalence community strongly indicate beta thalassemia major (ฮฒโฐ type).
- โConsanguineous marriages increase the risk of homozygous recessive disorders.
- โHPLC showing absent HbA confirms severe ฮฒโฐ thalassemia.
- โFamily screening and genetic counseling are essential for future pregnancies.
Frequently Asked Questions
Thalassemia is a quantitative defect โ reduced production of a normal globin chain. Hemoglobinopathy is a qualitative defect โ production of a structurally abnormal globin chain due to amino acid substitution, deletion or addition.
In thalassemia minor the marrow compensates for smaller cells by producing more of them, raising the RBC count despite low Hb. In iron deficiency, both cell number and hemoglobin content are reduced because iron is needed for cell production itself.
Yes โ sickle cell trait carriers are usually asymptomatic with a normal or near-normal smear. Diagnosis requires a sickling test, solubility test, or hemoglobin electrophoresis/HPLC.
Quick Revision
10-Minute ReviewKey Takeaways
- Reduced globin chain production causes thalassemia; alpha or beta chains may be affected.
- Structural globin abnormalities cause hemoglobinopathies such as HbS, HbE, HbD and HbC.
- Beta thalassemia major presents in infancy with severe anemia and hepatosplenomegaly; predominantly HbF on HPLC.
- Beta thalassemia minor is a mild, well-compensated microcytic anemia with raised HbA2.
- Sickle hemoglobin causes red cell sickling under hypoxia, leading to vaso-occlusion and hemolysis.
- Genetic counseling and family screening are central to preventing severe inherited hemoglobin disorders.
Competency Checklist
Track Your MasteryReferences
- NIOS Hematology and Blood Bank Technique โ Lesson 19: Hemolytic Anemia Due to Abnormal Hemoglobin Synthesis.
- Dacie JV, Lewis SM. Practical Haematology. 11th ed.
- Weatherall DJ, Clegg JB. The Thalassaemia Syndromes. 4th ed.