C4A and hereditary angioedema: Even though C4 levels are usually decreased in HAE patients, it is not recommended to use this as a single screening tool due to its limited sensitivity and specificity, estimated at 81 and 85%, respectively.47The most recent guideline recommends to repeat C1-inhibitor function, C1-inhibitor protein, and C4 testing in patients to confirm the diagnosis.8Genetic sequencing is not recommended as a diagnostic tool for patients with HAE type 1 or 2.