How Angioedema Is Diagnosed

Angioedema can be hereditary, but most of the time it is not. There are diagnostic tests that can identify hereditary angioedema.

Angioedema that is not hereditary is normally diagnosed based on the appearance of the skin combined with a history of exposure to a substance that could have caused an allergic reaction. Sometimes, blood tests can support the diagnosis, but results are not specific in terms of associated abnormalities.

Self-Checks/At-Home Testing

You can check yourself or your child for angioedema. Usually, the signs you would check for are clearly visible on the surface of the skin, so you do not have to search for them.

Another way to check if you or your child has angioedema is to look at the list of ingredients of prepared food that you have consumed, in case it contains something you or a close family member has been allergic to in the past.

Labs and Tests

There are two main types of angioedema—a hereditary type and a non-hereditary type. The symptoms are similar, but the diagnostic tests that confirm each type are different.

Non-Hereditary Angioedema

Generally, angioedema that is not hereditary is a diagnosis based on your healthcare provider’s evaluation of your symptoms, your physical examination, and identification of an allergen. An allergen is a substance that triggers a strong immune reaction. Non-hereditary angioedema is also often spontaneous, meaning that there is no external trigger for the episode of angioedema.

Commonly used tests in the evaluation of angioedema include:

• Allergy Test: There are a variety of allergy tests. The most common involves a small skin prick with a small amount of the substance suspected of causing an allergy. If you have a reaction such as redness, bumps, swelling, or itching in the area of the prick, you are likely to have an allergy to the substance. You might be tested for several substances at a time, and if you have a reaction to one and not the others this is a strong sign of an allergy.
• Blood Test: Blood tests can detect elevated levels of immunological activity. Some signs of increased immune activity include elevated white blood cell levels, erythrocyte sedimentation rate (ESR), and anti-nuclear antibody (ANA). All of these, however, can signal a number of infections and immunological disorders, so they are not specific to angioedema.

Hereditary Angioedema

A genetic test and a blood test can identify this condition. It is more common to have the blood test.

• Screening Test: A blood test that measures C4 levels may be used as a screening blood test for hereditary angioedema. Low levels of C4 suggest an autoimmune disorder, and a low level would indicate that you need another more specific blood test to check for C1 inhibitor deficiency. If there is a high likelihood that you have hereditary angioedema, you would need a follow up blood test for C1 inhibitor deficiency. But if you have a low chance of having hereditary angioedema, a normal C4 strongly suggests that you do not have the condition.
• Blood Test: The blood test identifies a defect in the C1 esterase inhibitor protein (C1-INH). The C1-INH level can be lower than normal, or it may be normal but not functional. C1-INH is a protein that works to keep your immune system in check so that it will not overreact. A hereditary genetic defect causes type I angioedema, which results in abnormal C1-INH levels or type ll angioedema, which causes abnormal C1-INH activity. 
• Genetic Test: The specific gene mutations that cause angioedema can be found on the SERPING1 gene for type l and ll angioedema. Mutations on the F12 gene can be identified for type lll angioedema. The exact consequence of this abnormality is not well understood. 

Hereditary angioedema is inherited directly from parents with an autosomal dominant pattern, which means that if a person has the gene for this condition, symptoms of the disease will develop. Because it is autosomal dominant, whichever parent you inherit the gene for angioedema type l, ll or lll also should have symptoms of the condition because it is a dominant trait. Hereditary angioedema is not a common, affecting only about 1 in 50,000 people.

Imaging

Imaging is not normally helpful in diagnosing angioedema. In some situations, particularly when there is shortness of breath or when gastrointestinal problems such as stomach discomfort, nausea, and diarrhea are problematic, diagnostic imaging tests to rule out other illnesses may be needed.

Differential Diagnosis 

There are a few other conditions that may produce symptoms similar to those of angioedema.

Acute Contact Dermatitis

A condition that is very similar to angioedema, contact dermatitis results from contact with a substance that produces a hypersensitivity. The conditions are similar and it may be hard to tell the difference. Acute contact dermatitis of the face is often misdiagnosed as angioedema, as it can cause severe swelling of the facial skin, especially after contact with hair dye.

Infection or Injury

Edema is swelling of any part of the body. It can occur in response to an injury or an infection, in which case it can occur quickly and abruptly, similar to the edema of angioedema.

Like angioedema, edema due to injury or infection may also involve only an isolated region of the body. There are subtle differences between the edema, however, including a possible fever and more severe pain if the cause is an injury or infection.

Heart or Kidney Failure

The edema of heart failure or kidney failure is usually gradual. Most of the time, edema is not the first symptom of these conditions.

A few important differences are that edema of heart failure or kidney failure is usually symmetric, which does not have to be the case in angioedema. The edema of angioedema is not pitting, while edema of heart failure or kidney failure is pitting edema.

Deep Vein Thrombosis (DVT)

DVT causes swelling of one part of the body, usually the lower leg. Like angioedema, it may be sudden, painless, and asymmetric. A DVT can cause a pulmonary embolism, resulting in a respiratory emergency. A DVT is not expected to be accompanied by swelling of the lips or eyes.

Lymphedema

Blockage of the flow of fluid throughout the body can occur due to lymphatic system obstruction. This can occur after some types of surgery, particularly cancer surgery. Some medications can produce lymphedema as well. It is usually characterized by swelling in one arm and rarely occurs without a medical history that suggests a lymphatic system cause.