Which feature best distinguishes sickle cell disease (HbSS) from sickle cell trait (HbAS) in an Indian patient presenting with recurrent pain crises?

Question

Accepted Answer

C. Vaso-occlusive pain crises occurring in childhood. ## Distinguishing Sickle Cell Disease from Sickle Cell Trait

### Clinical Presentation Difference

**Key Point:** Vaso-occlusive pain crises in childhood are pathognomonic for sickle cell disease (HbSS), not trait. Patients with HbAS rarely experience crises except under extreme stress (high altitude, severe infection, or severe dehydration).

### Comparison Table

| Feature | HbSS (Disease) | HbAS (Trait) |
| --- | --- | --- |
| **Genotype** | Homozygous (β^S^/β^S^) | Heterozygous (β^A^/β^S^) |
| **HbS percentage** | 80–95% | 35–45% |
| **Vaso-occlusive crises** | Frequent, from childhood | Rare; only extreme stress |
| **Hemolysis** | Chronic, severe | Minimal or absent |
| **Organ damage** | Progressive (spleen, kidney, bone) | None |
| **Life expectancy** | Reduced (median ~50–60 years) | Normal |
| **Sickling under hypoxia** | Occurs readily | Occurs only under severe hypoxia |

### Why Other Options Are Misleading

**High-Yield:** HbS is present on electrophoresis in BOTH disease and trait — this is not discriminatory. Similarly, both will show positive solubility tests because both contain HbS. The key difference is the **clinical phenotype**: only HbSS causes recurrent childhood pain crises.

**Clinical Pearl:** Patients with sickle cell trait are often asymptomatic and discovered incidentally on screening. They do NOT require prophylactic penicillin or transfusion support. The presence of recurrent pain crises in childhood is the red flag for homozygous disease.

Answer

A. Presence of HbS on hemoglobin electrophoresis

Answer

B. Positive sickle cell screening test (solubility test)

Answer

D. Sickling of RBCs only under severe hypoxia or dehydration

Which feature best distinguishes sickle cell disease (HbSS) from sickle cell trait (HbAS) in an Indian patient presenting with recurrent pain crises?

Explanation

Distinguishing Sickle Cell Disease from Sickle Cell Trait

Clinical Presentation Difference

Comparison Table

Why Other Options Are Misleading

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Feature	HbSS (Disease)	HbAS (Trait)
Genotype	Homozygous (β^S/β^S)	Heterozygous (β^A/β^S)
HbS percentage	80–95%	35–45%
Vaso-occlusive crises	Frequent, from childhood	Rare; only extreme stress
Hemolysis	Chronic, severe	Minimal or absent
Organ damage	Progressive (spleen, kidney, bone)	None
Life expectancy	Reduced (median ~50–60 years)	Normal
Sickling under hypoxia	Occurs readily	Occurs only under severe hypoxia