Regarding the hematologic and hemolytic features of sickle cell disease, all of the following are true EXCEPT:

Question

Accepted Answer

B. Haptoglobin levels are elevated as a marker of ongoing intravascular hemolysis. ## Hematologic Features of Sickle Cell Disease

### Hemolytic Anemia

**Key Point:** Sickle cell disease is characterized by chronic hemolytic anemia due to shortened RBC survival. Normal RBCs survive ~120 days; sickled RBCs survive only 10–20 days due to repeated sickling-unsickling cycles, membrane damage, and splenic sequestration/destruction.

### Reticulocytosis

**High-Yield:** The bone marrow responds to chronic hemolysis with marked reticulocytosis (often 5–15% or higher). This is a compensatory response to maintain adequate hemoglobin levels. Reticulocyte count is a useful marker of hemolytic activity and bone marrow reserve.

### Indirect Hyperbilirubinemia

**Clinical Pearl:** Chronic hemolysis releases hemoglobin from destroyed RBCs. Hemoglobin is converted to bilirubin via heme oxygenase and biliverdin reductase. The unconjugated bilirubin is transported to the liver and conjugated, but the rate of RBC destruction often exceeds hepatic conjugation capacity, leading to elevated indirect (unconjugated) hyperbilirubinemia. Patients may develop pigment gallstones (bilirubin stones) from chronic hyperbilirubinemia.

### Haptoglobin Levels

**Warning:** Haptoglobin levels are **DECREASED** (not elevated) in hemolytic anemias, including sickle cell disease. Haptoglobin is a plasma protein that binds free hemoglobin released from lysed RBCs. In intravascular hemolysis, free hemoglobin saturates and depletes haptoglobin, leading to low or absent serum haptoglobin. This is a classic laboratory finding in hemolytic anemia.

**Mnemonic:** **DECREASED Haptoglobin = Hemolysis** — both start with 'H'.

| Laboratory Finding | Sickle Cell Disease | Interpretation |
| --- | --- | --- |
| RBC survival | 10–20 days (vs. 120 days normal) | Chronic hemolysis |
| Reticulocyte count | Markedly elevated (5–15%) | Bone marrow compensation |
| Indirect bilirubin | Elevated | RBC destruction → heme → bilirubin |
| Haptoglobin | **DECREASED/ABSENT** | Free Hb binds and depletes haptoglobin |
| LDH | Elevated | Intracellular enzyme release from hemolysis |
| Hemoglobin | Low (7–10 g/dL typical) | Chronic hemolysis |

**High-Yield:** In hemolytic anemias, the triad of elevated reticulocytes, elevated indirect bilirubin, and **DECREASED haptoglobin** is pathognomonic.

Answer

A. Indirect hyperbilirubinemia is elevated due to increased unconjugated bilirubin from RBC destruction

Answer

C. Reticulocytosis is markedly elevated as a compensatory response to chronic hemolysis

Answer

D. Hemolytic anemia results from reduced red cell survival (10–20 days) compared to normal RBCs (120 days)

Regarding the hematologic and hemolytic features of sickle cell disease, all of the following are true EXCEPT:

Explanation

Hematologic Features of Sickle Cell Disease

Hemolytic Anemia

Reticulocytosis

Indirect Hyperbilirubinemia

Haptoglobin Levels

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Laboratory Finding	Sickle Cell Disease	Interpretation
RBC survival	10–20 days (vs. 120 days normal)	Chronic hemolysis
Reticulocyte count	Markedly elevated (5–15%)	Bone marrow compensation
Indirect bilirubin	Elevated	RBC destruction → heme → bilirubin
Haptoglobin	DECREASED/ABSENT	Free Hb binds and depletes haptoglobin
LDH	Elevated	Intracellular enzyme release from hemolysis
Hemoglobin	Low (7–10 g/dL typical)	Chronic hemolysis