Question

A 32-year-old mountaineer has a haematocrit of 70%. What is the possible explanation?

• A. Polycythemia with relative dehydration
• B. High altitude cerebral oedema
• C. High altitude pulmonary oedema
• D. Haemodilution

Hint:

Altitude raises red cell mass and dehydration concentrates the plasma, both lifting the haematocrit.

Answer 1

The Correct Option is A

Step 1: Interpret the haematocrit. A haematocrit of 70% is markedly raised (normal roughly 40 to 50%), meaning the proportion of red cells in blood is very high.
Step 2: Apply the altitude physiology. Chronic exposure to the low oxygen of high altitude stimulates erythropoietin release, driving secondary polycythemia and a true rise in red cell mass.
Step 3: Add the fluid factor. At altitude, low humidity, increased respiratory water loss and reduced intake cause relative dehydration, which contracts plasma volume and concentrates the blood further, pushing the haematocrit even higher.
Step 4: Reject the others. High altitude cerebral oedema and high altitude pulmonary oedema are acute life-threatening syndromes defined by neurological signs or breathlessness, not by a high haematocrit. Haemodilution would lower, not raise, the haematocrit.
Step 5: Conclude. The combination of secondary polycythemia and relative dehydration best explains a haematocrit of 70%.