1. Hemoglobin Structure & Genes
Hemoglobin = tetramer
2 α-globin chains + 2 non-α chains (β, γ, or δ), each bound to a heme (iron) group.
Genes
• HBA1 & HBA2 (α-globin) → Chromosome 16 (4 alleles total)
• HBB (β-globin) → Chromosome 11 (2 alleles total)
| Hemoglobin | Globin chain | Normal adult level |
|---|
| Hb A | α2β2 | >90–95% |
| Hb A2 | α2δ2 | 2.2–3.5% |
| Hb F | α2γ2 | <2.0% (reaches adult level by ~2 yrs) |
2. HPLC Windows Cheat-Sheet
HPLC separates Hb fractions by retention time → quantifies HbA, A2, F and screens for variants.
| Window | Normal Hb | Key abnormal findings that elute there |
|---|
| F window | Hb F | — |
| A window | Hb A | — |
| A2 window | Hb A2 | β-thal trait (3.7–8%), Hb Lepore (8–15%), HbE (25–30% trait, >90% disease), Hb D-Iran (30–50%) |
| D window | — | HbD-Punjab, Hb G-Philadelphia |
| S window | — | Hb S |
| C window | — | Hb C, Hb Constant Spring |
3. Step-Wise Interpretation Approach
① Patient History
- Family history of thalassemia/SCD/other Hb-opathy
- Clinical signs: anemia, jaundice, splenomegaly
- Transfusion in the last 3–4 months
⚠ CRITICAL: a recent transfusion invalidates the HPLC result.
② Basic Screening
- CBC indices (MCV, MCH)
- Ferritin — rules out iron deficiency (can falsely lower HbA2, masking β-thal trait)
- Sickling test
- HPLC analysis
③ Advanced Testing
- Molecular/genetic testing when HPLC is inconclusive
- Required to confirm α-thalassemia (silent on HPLC except low A2 + double peaks)
Normal vs Abnormal HPLC
| Type | Definition |
|---|
| Normal HPLC | Normal hemoglobins + normal percentage of each |
| Abnormal HPLC | Normal Hbs but abnormal % (high/low) OR abnormal (variant) hemoglobins present |
📌 Golden rule: Two mutations in the SAME globin gene (i.e., inherited from both parents) are required to produce clinical disease. One mutation = trait/carrier (usually asymptomatic).
4. Abnormal HbA2 — the "Carrier" Number
LOW HbA2
- Iron deficiency anemia
- Alpha thalassemia / variant
- Delta thalassemia / variant
- HbH disease (α-thal) — also shows "early double peak" on HPLC graph
HIGH HbA2
- Beta thalassemia trait
- Elution of other abnormal Hbs mimicking A2 (Hb Lepore, HbE, HbD-Iran, Hb Sheffield)
| % at A2 window | Most likely |
|---|
| 3.5–8.0% | β-thal trait, Sβ⁺-thal |
| 3.5–4.5% | Hb AS, SC, SS, CC (co-elution, not true elevated A2) |
| 8–15.0% | Hb Lepore |
| 25–30% | Hb E trait |
| >60% | Hb EE / Hb Eβ-thal |
📌 Iron deficiency can falsely lower HbA2 and mask an underlying β-thal trait → always check ferritin, correct IDA, and re-test before excluding β-thal trait.
5. Abnormal HbF (>2%) — Decision Tree
High Hb F is normal in babies <6 months. In adults, first exclude acquired secondary causes, then sort by CBC:
| Pattern | Likely Diagnosis |
|---|
| Isolated high HbF + normal CBC | Hereditary Persistence of Fetal Hemoglobin (HPFH) — benign |
| High HbF + abnormal CBC | Homozygous β-thalassemia or β/δ-thalassemia |
| High HbF + other abnormal Hb (e.g., HbS) | Likely related to sickle cell disease (compensatory HbF rise) |
6. Abnormal Hemoglobin Variants — Beta Mutations
| Abnormal Hb | Trait (%) | Disease (%) |
|---|
| Hb S (sickle) | 30–40% | >40–50% |
| Hb S-Oman | 12–30% | — (no reported homozygous state) |
| Hb E (elutes in A2 window) | 15–30% | >60% |
| Hb D (Punjab) | 30–50% | 80–90% |
| Hb C | <50% | >50% |
📌 Hb S-Oman: unique double β-globin mutation (β6 Glu→Val + β121 Glu→Lys, same 2nd mutation as Hb O-Arab) → "super-sickling." Acts like disease even as a carrier. No homozygous form reported. Hb S / Hb S-Oman compound heterozygote behaves like sickle cell anemia — transfusion-dependent from childhood.
Alpha-chain mutations (rare, mostly clinically insignificant): Hb Fontainebleau, Hb Constant Spring, Hb G-Philadelphia.
7. Alpha Thalassemia — Patterns of Inheritance
📌 Thalassemias (α, β, δβ) are quantity disorders → HPLC shows no abnormal hemoglobin, only abnormal percentages (± early double peaks for α-thal).
| Alleles affected | Genotype | Description |
|---|
| One (silent carrier) | (–/α α/α) | 3 genes enough for normal Hb; slightly ↓MCV/MCH |
| Two — cis (α-thal-1, Asian) | (–/– α/α) | Both α genes deleted on same chromosome |
| Two — trans (α-thal-2, African) | (–/α –/α) | Trait, mild microcytic hypochromic anemia, near-normal erythropoiesis |
| Three | (–/– –/α) | Hb H disease — unstable, high-affinity Hb (Hb Barts γ4, Hb H β4) |
| Four | (–/– –/–) | Incompatible with life outside uterus — hydrops fetalis, all Hb Barts |
📌 If report reads "possible α-thalassemia / cannot exclude" → the partner needs genetic testing to confirm α-thal, but only if HbH disease is suspected.
8. Delta (δ) Variants & the HbA2′ Trap
Delta-Thalassemia
↓ or absent δ-chain → lowers HbA2, can mask β-thal trait. Usually asymptomatic.
Delta-Beta Thalassemia
Deletion of both δ and β genes → ↑ HbF (γ compensates), normal/low A2. Heterozygous = mild/asymptomatic; homozygous = mild anemia.
Structural HbA2 Variants
e.g., Hb A2-Saint-Étienne, Hb A2-Marseille — silent but can distort A2 measurement.
📌 Hb A2′ (Hb A2-prime) can present as low HbA2 alone. It splits the A2 peak into TWO peaks — one at the true A2 window, one at the S window (usually a trace, 1–2%). Add both peaks together to get the true HbA2 value before concluding β-thal status (see Case 13 below).
9. Disease Quick-Cards
β-Thalassemia Major
Dx in first 2 yrs (usually 3–6 mo). Severe anemia, hepatosplenomegaly, growth retardation, delayed puberty, bone deformities, frequent infection.
Transfusion-dependent (TDT) lifelong. Tx: transfusion, chelation, BMT.
β-Thalassemia Trait (carrier)
Reduced/absent β-chain synthesis. Mild → asymptomatic. Non-transfusion-dependent (NTDT).
Hb Dhofar (Oman-specific)
Phenotype = severe thalassemia intermedia despite Hb often >8 g/dL. Severe thalassemic facies, hepatosplenomegaly, stunted growth, delayed puberty.
Homozygous or compound het w/ β-thal → start regular transfusions once diagnosed.
Sickle Cell Disease (HbSS)
β6 Glu→Val. RBCs rigid/sickle-shaped → hemolysis + vaso-occlusion.
Multi-organ: brain (stroke), lung (ACS, HTN), heart failure, splenic autosplenectomy, priapism, hand-foot syndrome, retinopathy, leg ulcers.
Hemoglobin C (trait/CC)
Phenotypically normal alone; target cells ± HbC crystals on smear. Clinically significant only combined with other variants (e.g. HbSC).
Hemoglobin D-Punjab
Asymptomatic, normal/mild CBC changes. Benign as trait, but combos matter: HbD/HbS, HbD/β-thal, HbD/HbE.
HbSC Disease
Intermediate severity. Hb higher than HbSS. Less frequent crises; dactylitis uncommon but AVN ↑; retinal disease common (proliferans, vitreous hemorrhage); splenic sequestration (child & adult).
HbSD Disease (S/D-Punjab)
Moderate–severe, can resemble HbSS. Mild-mod hemolysis + sickling crises, persistent splenomegaly, macrocytosis, early childhood infections + pain crises.
HbSE Disease
Usually mild–moderate. Compensated hemolysis, splenomegaly, splenic infarction risk during flights, occasional pain crises. Rare severe complications (VOC, ACS, stroke) reported.
10. Practice Cases 1–14 — Applied Compatibility Reasoning
📌 General compatibility rule (autosomal recessive logic): if one partner carries a trait/disease and the other is genetically normal for that gene → Compatible (no risk of an affected homozygous/compound-het child, though children may be obligate carriers). If both partners carry a trait/variant of the same or interacting globin gene → Non-Compatible (up to 25% risk per pregnancy of disease/severe compound heterozygous state) — refer for genetic counselling.
| Case | Male partner | Female partner | Verdict & teaching point |
|---|
| 1 |
HbF 89.9%, A2 4.5%, Hb 7 → β-thal MAJOR |
Normal HPLC, ferritin 225 → Normal |
Compatible — partner not a carrier, so no risk of an affected child (all offspring will be obligate carriers only). |
| 2 |
Hb13, A2 4.6% → β-thal trait |
Hb8.1, MCV67, ferritin 3, A2 2% → Iron-deficiency anemia (may mask β-thal trait) |
Correct IDA & re-test before final call — classic IDA-masks-β-thal-trait pitfall. |
| 3 |
Hb 11.6, MCV 65.6, "Hb Dhofar 14.2%" detected → Hb Dhofar trait (Oman-specific variant) |
Partner must be screened for Hb Dhofar/β-thal — compound state = severe thalassemia intermedia. |
| 4 |
HbS 23.5%, A2 4.1% → Sickle cell trait (± coexisting β-thal trait) |
HbS 33% → Sickle cell trait |
Non-Compatible — AS × AS → 25% risk of Sickle Cell Disease (HbSS) per pregnancy. |
| 5 |
HbS 74.3%, HbF 13.9%, HbA 6.2% → Sickle Cell Disease (HbSS) |
Normal HPLC → Normal |
Compatible — partner normal; all offspring obligate AS carriers, none affected. |
| 6 |
A2 4.6% (no HbS) → β-thal trait |
HbA ~0%, "S-window" 89.7%, A2 6.1% → Sβ⁰-thalassemia (HbA absent + high HbS + high A2 = compound het, not simple SS) |
Non-Compatible — risk of severe Sβ-thal combination in offspring. |
| 7 |
HbC 92.9%, HbS 0% → Homozygous Hb C disease (CC) — usually benign |
HbS 36% → Sickle cell trait |
Non-Compatible — risk of HbSC disease in offspring. |
| 8 |
HbS 32% → Sickle cell trait |
HbD 91.4%, A2 0.8% → Homozygous Hb D (DD) |
Non-Compatible — risk of HbSD disease (moderate–severe) in offspring. |
| 9 |
HbF 82.1%, A2 5.7% → β-thal MAJOR |
"HbE 20.6% detected" → Hb E trait |
Non-Compatible — risk of HbE/β-thalassemia (can be severe disease). |
| 10 |
"Hb S-Oman 17% detected" → Hb S-Oman carrier |
Normal HPLC → Normal |
Compatible — no HbS present in partner, so no super-sickling compound-het risk; still counsel that S-Oman carriers can be symptomatic themselves. |
| 11 |
Normal HPLC → Normal |
A2 5.6% → β-thal trait |
Compatible — partner normal, no risk of β-thal major in offspring. |
| 12 |
A2 1.6% (low), platelets 926 (reactive) → possible iron deficiency |
MCV 51.4, Hb 7.2, A2 0.9%, "early double peaks" → suspect α-thalassemia (possible HbH disease) |
Needs molecular/genetic testing — HPLC alone cannot confirm α-thal; partner testing required only if HbH disease confirmed. |
| 13 |
A2 1.4% + "HbS" 1.2%, comment: "Total HbA2 = 2.6%" → Hb A2′ (delta variant), true A2 normal |
A2 4.2% → β-thal trait |
Compatible — classic HbA2′ teaching case: don't mistake the split A2 peak for real HbS trait; sum the two peaks first. |
| 14 |
HbF 12.2%, A2 2.1%, mild microcytosis → δβ-thalassemia trait (High F + abnormal CBC, not high enough for major) |
A2 4.2% → β-thal trait |
Non-Compatible — combination can produce a thalassemia-intermedia-like phenotype; refer for counselling. |
Note: exact "compatible/non-compatible" checkboxes in the source workshop slides were left blank for trainees to fill in live — the verdicts above are derived using standard autosomal-recessive genetic-counselling logic and the workshop's own teaching points, so cross-check against your instructor's official answer key.
11. Final Exam Pearls (Rapid Recall)
Before trusting any HPLC: ask about transfusion in the last 3–4 months (invalidates result) and check ferritin (low ferritin → falsely low A2 → masks β-thal trait).
Thalassemias = quantity problem → normal Hb types, abnormal %, ± early double peak (α-thal). Structural variants (S/C/D/E) = quality problem → an actual new peak appears.
Two mutations, same gene, disease. One mutation = trait. Two different interacting genes (e.g. HbS + HbC, HbS + HbD, HbE + β-thal) can still produce a compound-heterozygous disease.
α-thalassemia is invisible on Hb electrophoresis/HPLC except for low A2 ± early double peaks — genetic testing is the only way to confirm gene deletions (esp. before labeling as HbH disease).
Hb S-Oman = unique to Oman, "super-sickler," symptomatic even as carrier; S/S-Oman compound het = clinically like Sickle Cell Anemia.
Hb Dhofar = unique to Oman; even with Hb >8 g/dL, behaves as severe thalassemia intermedia; start transfusions as soon as diagnosed (homozygous/compound het with β-thal).