Rare diseases · Sign or symptom
Anemia
Low number of red blood cells or hemoglobin
HP:0001903
What it means
A reduction in erythrocytes volume or hemoglobin concentration.
Anemia is not a specific entity but can result from many underlying pathologic processes. The three main causes of anemia are blood loss, decreased or faulty red blood cell production, and increased destruction of red blood cells. Various classifications are in clinical use including a classification according to the mean corpuscular volume (MCV) of the erythrocytes: microcytic, macrocytic, or normocytic. Anemias can also be classified according to variations in cell size and shape, as reflected by the red-cell distribution width (RDW). Additionally, anemias can be classified into those of inadequate production and hemolytic anemias.
In everyday care
Most people with this sign do not have a rare disease — it appears in common conditions far more often. These general reference pages cover the same topic:
Rare diseases that can present with this227
Very common80–99%
52- Acute myelomonocytic leukemia
- Anti-glomerular basement membrane disease
- Atherosclerosis-deafness-diabetes-epilepsy-nephropathy syndrome
- Autosomal recessive generalized dystrophic epidermolysis bullosa, intermediate form
- Autosomal recessive generalized dystrophic epidermolysis bullosa, severe form
- Autosomal recessive malignant osteopetrosis
- Beta-thalassemia
- Beta-thalassemia-X-linked thrombocytopenia syndrome
- Congenital atransferrinemia
- Congenital dyserythropoietic anemia type III
- Congenital progressive bone marrow failure-B-cell immunodeficiency-skeletal dysplasia syndrome
- Delta-beta-thalassemia
- Drug-induced lupus erythematosus
- Dyskeratosis congenita
- Fabry disease
- Familial hemophagocytic lymphohistiocytosis
- Fanconi anemia
- Fetal parvovirus syndrome
- Gaucher disease
- Ghosal hematodiaphyseal dysplasia
- Glycogen storage disease due to muscle phosphofructokinase deficiency
- Hemoglobin Bart's fetalis syndrome
- Hemoglobin C-beta-thalassemia syndrome
- Hemoglobin E-beta-thalassemia syndrome
- Hemolytic anemia due to red cell pyruvate kinase deficiency
- Hepatoportal sclerosis
- Hereditary orotic aciduria
- Hereditary persistence of fetal hemoglobin-beta-thalassemia syndrome
- Hydatidiform mole
- Intellectual disability-cataracts-calcified pinnae-myopathy syndrome
- Juvenile polyposis of infancy
- Lethal hemolytic anemia-genital anomalies syndrome
- Leukocyte adhesion deficiency type II
- Macrophage activation syndrome
- Malaria
- MALT lymphoma
- Mitochondrial myopathy and sideroblastic anemia
- Mucopolysaccharidosis-like syndrome with congenital heart defects and hematopoietic disorders
- Multifocal infantile hemangioma with extracutenous involvement
- Paroxysmal nocturnal hemoglobinuria
- Primary hyperoxaluria type 1
- Primary intestinal lymphangiectasia
- Reticular dysgenesis
- Rosaï-Dorfman disease
- Severe congenital hypochromic anemia with ringed sideroblasts
- Shwachman-Diamond syndrome
- Stormorken-Sjaastad-Langslet syndrome
- Transaldolase deficiency
- Umbilical cord ulceration-intestinal atresia syndrome
- Wilson disease
- X-linked sideroblastic anemia
- X-linked sideroblastic anemia and spinocerebellar ataxia
Common30–79%
27- 21q deletion syndrome
- 3-hydroxy-3-methylglutaric aciduria
- Abetalipoproteinemia
- Acquired hemophagocytic lymphohistiocytosis associated with malignant disease
- Acute erythroid leukemia
- Acute monoblastic/monocytic leukemia
- Acute promyelocytic leukemia
- Adult-onset Still disease
- Albers-Schönberg osteopetrosis
- Alpha-heavy chain disease
- Alveolar echinococcosis
- Aseptic abscess syndrome
- Autosomal dominant generalized epidermolysis bullosa simplex, severe form
- Autosomal dominant Kenny-Caffey syndrome
- Bazex syndrome
- Brucellosis
- Castleman disease
- Cernunnos-XLF deficiency
- Chronic neurovisceral acid sphingomyelinase deficiency
- CINCA syndrome
- Cogan syndrome
- Congenital amegakaryocytic thrombocytopenia
- Congenital rubella syndrome
- Cronkhite-Canada syndrome
- Diffuse alveolar hemorrhage
- Dopamine beta-hydroxylase deficiency
- Eosinophilic gastroenteritis
The 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, and Orphanet separately records 5 diseases where this sign is specifically absent. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Anaemia · Decreased haemoglobin · Decreased hemoglobin · Low number of red blood cells or haemoglobin
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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.