Can hereditary hemorrhagic telangiectasia cause secondary erythrocytosis (elevated red blood cell count)?

Can HHT Cause Elevated Red Blood Cells?

No, HHT does not cause elevated red blood cells (erythrocytosis); instead, it characteristically causes anemia and low red blood cell counts due to chronic bleeding. 1

Why HHT Causes Low, Not High, Red Blood Cells

• Chronic blood loss is the hallmark of HHT, with recurrent epistaxis occurring in more than 90% of adults and gastrointestinal bleeding from telangiectasias leading to iron deficiency anemia in approximately 50% of patients 1, 2, 3

• Iron deficiency anemia from bleeding is the dominant hematologic manifestation, causing fatigue, reduced exercise tolerance, and hair loss rather than erythrocytosis 1

• All adults with HHT should be screened for iron deficiency and anemia regardless of symptoms (strong recommendation, high quality evidence), as this is an expected consequence of the disease 1

Exception: Secondary Erythrocytosis from Pulmonary AVMs

While HHT itself causes anemia, there is one specific scenario where elevated red blood cells could theoretically occur:

• Pulmonary AVMs create right-to-left shunts causing chronic hypoxemia, which could theoretically trigger compensatory erythrocytosis 1, 4

• However, this is extremely rare in practice because the chronic bleeding and iron deficiency from HHT overwhelmingly dominate the clinical picture, preventing any compensatory erythrocytosis from developing 1

• Pulmonary AVMs are more frequent in HHT type 1 (40% incidence) compared to HHT type 2 (14% incidence), but even in these patients, anemia from bleeding is far more common than erythrocytosis 5, 6, 2

Clinical Pitfall to Avoid

• If a patient with HHT presents with elevated red blood cells, investigate for an alternative cause of erythrocytosis unrelated to their HHT, as this would be highly atypical 1

• The expected hematologic finding in HHT is anemia with low hemoglobin, often requiring oral or intravenous iron replacement therapy 1

• Approximately 43% of patients are hypoxemic at rest due to pulmonary AVMs, yet this does not translate into clinically significant erythrocytosis because of concurrent blood loss 4