Angioedema is a condition characterized by swelling underneath the skin that usually appears around the lips and eyes. It can occur as part of an allergic reaction (acute allergic angioedema), as a response to certain medications (non-allergic angioedema), or be genetic (hereditary angioedema), the results of a malfunctioning immune system (acquired angioedema), or appear without a known cause (idiopathic angioedema).
The disease is similar to hives or urticaria, but while hives are swelling in the upper layers of the skin (the epidermis and dermis), angioedema is swelling in layers below the skin (the subcutaneous and submucosal layers). Angioedema and hives can occur independently or at the same time.
To diagnose the condition, the doctor will try to figure out what may have caused the disease, review the symptoms, examine the affected area, carefully analyze the patient’s medical history and perform some tests to distinguish the different types of angioedema.
If symptoms are suspected to be caused by an allergy to external substances, such as food or medications, the patient may be directed to a specialist who may perform a skin prick test or a blood test.
Skin prick test
A skin prick test is one of the most common diagnostic tests for allergies. It attempts to provoke a small, controlled, allergic response in the skin. A drop of liquid that contains a substance the patient may be allergic to is put on the forearm. Then, the skin under the drop is gently pricked with a needle to see whether there is a reaction. If the patient is allergic to the substance, a raised, red, itchy bump (wheal) that may look like a mosquito bite will appear within 15 minutes. The test is painless and very safe. Patients should not take antihistamines before the test because they can interfere with the results.
A sample of the patient’s blood is collected and analyzed for specific antibodies that the immune system produces in response to an allergen.
Because non-allergic angioedema is induced by renin-angiotensin-aldosterone-system (RAE) blockers and angiotensin-converting enzyme (ACE) inhibitors, the medical history of the patient is usually sufficient to diagnose this type of angioedema.
If no mutations are found in the SERPING1 gene, the F12 gene is analyzed to see if the patient has hereditary angioedema type 3.
Acquired angioedema occurs when levels of C1-INH are too low due to antibodies mistakenly targetting it for destruction. In this case, blood tests can be used to evaluate the level of C1-INH and anti-C1-INH antibodies in the blood.
If all the above tests fail to produce negative results the patient may be diagnosed with idiopathic angioedema, which simply means the cause is unknown.
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