Question
A 19-year-old man with established Sickle Cell Disease presents with fatigue and mild jaundice after recent exposure to cold weather. His baseline haemoglobin is around 85 g/L, but current labs show a drop to 50 g/L. A haemolytic episode is suspected.
Which laboratory value is most likely to be reduced in this situation?
A. Reticulocyte count
B. Direct (conjugated) bilirubin
C. Indirect (unconjugated) bilirubin
D. Serum haptoglobin
E. Lactate dehydrogenase
Answer:
D. Serum haptoglobin
Detailed Explanation
In a haemolytic crisis, especially in conditions like Sickle Cell Disease, there is accelerated destruction of red blood cells (RBCs).
Key mechanism:
- RBC breakdown → release of free haemoglobin into plasma
- Haptoglobin binds free haemoglobin → forms complex cleared by liver
- During massive haemolysis → haptoglobin gets consumed → levels fall
👉 Therefore: Low haptoglobin = marker of intravascular haemolysis
What happens to other parameters?
- Reticulocytes ↑
Bone marrow compensates → increased RBC production - Unconjugated bilirubin ↑
From breakdown of haem - Conjugated bilirubin → usually normal or mildly ↑
Only rises significantly in hepatobiliary disease - LDH ↑
Released from destroyed RBCs
High-Yield Concept
👉 Intravascular haemolysis triad:
- ↓ Haptoglobin
- ↑ LDH
- ↑ Unconjugated bilirubin
Cheat Sheet
Haemolytic Crisis (especially in SCD):
- Trigger: infection, cold, hypoxia
- Hb drop: acute (30–40 g/L)
- Key labs:
- Haptoglobin ↓↓↓
- Reticulocytes ↑
- LDH ↑
- Unconjugated bilirubin ↑
Golden rule:
👉 Haptoglobin is the best marker of intravascular haemolysis
Flash Cards
1. What happens to haptoglobin in haemolysis?
Decreases due to binding with free haemoglobin and consumption
2. Why is unconjugated bilirubin elevated in haemolysis?
Because haem breakdown produces indirect bilirubin
3. What happens to reticulocyte count in haemolytic anaemia?
Increases due to marrow compensation
4. Why is LDH elevated in haemolysis?
Released from destroyed red blood cells
5. What type of bilirubin rises in haemolysis?
Unconjugated (indirect) bilirubin
MCQs
MCQ 1
A patient with acute haemolysis is expected to have which combination?
A. High haptoglobin, low LDH
B. Low haptoglobin, high LDH
C. High conjugated bilirubin only
D. Low reticulocyte count
Answer: B
Explanation: Haemolysis → haptoglobin consumption (↓), RBC destruction → LDH ↑
MCQ 2
Which of the following is FALSE in haemolytic anaemia?
A. Reticulocyte count increases
B. Unconjugated bilirubin rises
C. Haptoglobin increases
D. LDH increases
Answer: C
Explanation: Haptoglobin decreases due to binding with free haemoglobin
MCQ 3
The primary function of haptoglobin is:
A. Transport iron
B. Bind free haemoglobin
C. Produce bilirubin
D. Stimulate erythropoiesis
Answer: B
Explanation: Haptoglobin binds circulating free haemoglobin preventing renal damage
MCQ 4
Which lab finding best indicates intravascular haemolysis?
A. Increased conjugated bilirubin
B. Decreased haptoglobin
C. Low LDH
D. Low reticulocyte count
Answer: B
Explanation: Haptoglobin is consumed during intravascular haemolysis
MCQ 5
In sickle cell haemolytic crisis, which change is most expected?
A. Decreased reticulocytes
B. Increased haptoglobin
C. Increased LDH
D. Decreased unconjugated bilirubin
Answer: C
Explanation: RBC destruction releases LDH → levels rise
Summary for Quick Exam Revision
Haemolytic crisis in sickle cell disease is characterized by rapid destruction of red blood cells leading to acute anaemia and jaundice. The key biochemical hallmark is low haptoglobin, as it binds free haemoglobin released during intravascular haemolysis and gets consumed. Simultaneously, LDH rises due to cell breakdown, and unconjugated bilirubin increases from haem metabolism. The bone marrow responds by increasing erythropoiesis, resulting in reticulocytosis. Conjugated bilirubin is typically not significantly elevated unless there is associated liver or biliary pathology. Among all lab parameters, haptoglobin is the most specific indicator of intravascular haemolysis, making it a high-yield exam concept.