Rare diseases · Sign or symptom
Polycythemia
Increased red blood cells
HP:0001901
What it means
Polycythemia is diagnosed if the red blood cell count, the hemoglobin level, and the red blood cell volume all exceed the upper limits of normal.
Rare diseases that can present with this14
Sometimes5–29%
6The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Abnormally shaped erythrocytes · Erythrocytosis · Polyglobulia
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.