Causes of Relative Erythrocytosis Analysis

Relative erythrocytosis is a condition where the concentration of red blood cells appears higher than normal, but the actual total red blood cell mass remains unchanged. This usually happens because the plasma volume has decreased.

Option Analysis

• High altitude: Leads to absolute erythrocytosis. The lower oxygen levels (hypoxia) stimulate the kidneys to produce more erythropoietin, increasing red blood cell production.
• Cardiorespiratory disease: Chronic conditions affecting the heart or lungs often cause hypoxia, stimulating erythropoietin and leading to absolute erythrocytosis.
• High-affinity haemoglobins: These abnormal haemoglobins bind oxygen more tightly, impairing oxygen delivery to tissues. This can trigger a compensatory increase in red blood cell mass, causing absolute erythrocytosis.
• Diuretics: These medications increase fluid loss from the body, potentially reducing plasma volume. A lower plasma volume concentrates the existing red blood cells, causing relative erythrocytosis.

Conclusion

Diuretics cause a decrease in plasma volume, which is the mechanism behind relative erythrocytosis. The other options stimulate increased production of red blood cells, leading to absolute erythrocytosis.