Does HHT Cause Elevated Red Blood Cell Counts?
No, HHT does not cause elevated red blood cell counts—it causes anemia. Approximately 50% of HHT patients experience iron deficiency anemia from chronic bleeding, making anemia the typical presentation rather than erythrocytosis 1. If a patient with HHT presents with elevated red blood cell counts, this is exceedingly rare and should prompt immediate investigation for alternative causes 1.
The Typical Hematologic Picture in HHT
HHT characteristically causes chronic bleeding leading to iron deficiency anemia, not erythrocytosis. The pathophysiology involves:
- Recurrent epistaxis (nosebleeds) affecting 90-95% of patients, typically beginning in childhood 2
- Gastrointestinal bleeding from telangiectasias in the stomach, small bowel, and colon 2, 3
- Chronic blood loss resulting in iron deficiency and anemia as the dominant hematologic manifestation 4, 5
The 2021 American Society of Hematology guidelines emphasize this by recommending screening for iron deficiency and anemia in all adults with HHT regardless of symptoms, precisely because bleeding and anemia are the expected complications 6, 7.
When Erythrocytosis Occurs in HHT: Investigate Alternative Causes
If you encounter an HHT patient with elevated red blood cell counts, this represents an atypical presentation requiring systematic evaluation 1:
Primary Diagnostic Considerations
Screen for pulmonary arteriovenous malformations (PAVMs) first, as these are the most likely HHT-related cause of erythrocytosis through chronic hypoxemia 1, 8:
- Use contrast echocardiography or chest CT as initial screening 1, 8
- PAVMs cause right-to-left shunting leading to chronic hypoxemia, which can stimulate erythropoietin production 5
Evaluate for hepatic AVMs using Doppler ultrasonography as first-line imaging, since these can contribute to abnormal erythropoietin production 1, 8:
- Note: Never perform liver biopsy in HHT patients due to catastrophic hemorrhage risk from vascular malformations 7, 1
Rule out coincidental polycythemia vera or other primary myeloproliferative disorders through hematology referral with JAK2 mutation testing and bone marrow evaluation if indicated 1, 8.
Management Algorithm Based on Findings
If PAVMs are identified causing hypoxemia-driven erythrocytosis:
- Perform percutaneous transcatheter embolization regardless of feeding artery size 1, 8
- This addresses both the erythrocytosis (by correcting hypoxemia) and prevents life-threatening neurological complications including paradoxical embolism, stroke, and cerebral abscess 1, 8
If no secondary cause is found:
- Refer to hematology for comprehensive evaluation of primary polycythemia 1
- Continue monitoring for evolution toward anemia, which would indicate progression of typical HHT bleeding manifestations 1
Critical Monitoring Considerations
Even in the rare HHT patient presenting with erythrocytosis, establish baseline iron studies (ferritin and transferrin saturation) 1:
- HHT patients may transition from erythrocytosis to iron deficiency if bleeding worsens over time 1
- Reassess hemoglobin and hematocrit at 1-month intervals to detect this evolution 1
Common Pitfall to Avoid
Do not assume erythrocytosis is a manifestation of HHT itself. The overwhelming majority of HHT patients present with anemia from chronic bleeding rather than elevated red blood cell counts 1. Erythrocytosis in an HHT patient represents either a complication (such as hypoxemia from PAVMs) or a coincidental separate disorder requiring distinct evaluation and management 1, 8.