Rare diseases · Sign or symptom
Decreased circulating complement C4 concentration
HP:0045042
What it means
Concentration of the complement component C4 in the blood circulation below the lower limit of normal.
Rare diseases that can present with this10
Common30–79%
5The 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 1 disease 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: Decreased serum complement C4 · Decreased serum complement C4 level
Tracking symptoms like this for someone? Eleplan keeps symptoms, diagnoses, medications and every specialist in one plan.
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.