Version July 2025
| Angioedema disorder | C4* | C1INH level | C1INH function | C1q | Other tests |
| Hereditary angioedema with C1INH deficiency type 1 (HAE-C1INH type 1) | Low | Low | Low (usually <50% of normal) | Normal | Genetic testing (not needed for diagnosis) |
| Hereditary angioedema with C1INH deficiency type 2 (HAE-C1INH type 2) | Low | Normal or elevated | Low (usually <50% of normal) | Normal | Genetic testing (not needed for diagnosis) |
| Hereditary angioedema with factor XII gene mutations (HAE-FXII) | Normal | Normal | Normal | Normal | Mutations in gene for factor XII |
| Hereditary angioedema with angiopoietin 1 gene mutations (HAE-ANGPT1) | Normal | Normal | Normal | Normal | Mutations in gene for angiopoietin 1 |
| Hereditary angioedema with plasminogen gene mutations (HAE-PLG) | Normal | Normal | Normal | Normal | Mutations in gene for plasminogen |
| Hereditary angioedema with kininogen 1 gene mutations (HAE-KNG1) | Normal | Normal | Normal | Normal | Mutations in gene for kininogen 1 |
| Hereditary angioedema of unknown origin (HAE-U) | Normal | Normal | Normal | Normal | |
| Acquired angioedema with C1INH deficiency (AAE-C1INH) | Low | Normal or low | Low (usually <50% of normal) | Normal or low¶ | Anti-C1INH antibodies (not needed for diagnosis) |
| Idiopathic acquired angioedema (histaminergic or nonhistaminergic) (AAE-IH or AAE-InH) | Normal | Normal | Normal | Normal | |
| ACE inhibitor-associated angioedema (AAE-ACEI) | Normal | Normal | Normal | Normal |
AAE: acquired angioedema; ACEI: angiotensin-converting enzyme inhibitor; C1INH: C1 inhibitor; HAE: hereditary angioedema.
* In HAE-C1INH types 1 and 2, C4 is always low during an attack (with one published exception) and are chronically low in the majority of patients.
¶ There are rare forms of acquired angioedema in which C1q levels are normal. Refer to the UpToDate topics on acquired C1 inhibitor deficiency for details.
