How Urticaria (Hives) Is Diagnosed

Diagnosing the underlying cause of urticaria, or hives, whether it is acute or chronic, is important to help manage symptoms, decrease recurrences, guide treatment decisions, and most importantly, prevent possible complications. Your doctor will review your medical history, perform a physical exam, and may run tests that aim to detect food allergies, infection, autoimmune disease, or physical causes.

While many forms of urticaria can resolve after the cause is eliminated, others may require further treatment. Getting to the bottom of what is causing your hives is the first step in determining the outcome of your case.

Most times, the cause of urticaria is obvious. If you are stung by a bee and break out in hives, for example, you have your answer. In a similar way, most cases are diagnosed based on your history and clinical symptoms.

A study in the World Allergy Organization Journal reviewed 82 medical articles and recommended an urticaria checklist for your doctor that includes the following:

• Dates, times, and duration of hives
• Depression, anxiety, or stress
• Family history of hives
• Dyspepsia or peptic ulcer disease (H. pylori infection)
• Foods, especially if you have tried something new
• Medications and supplements, both prescription and over-the-counter
• Menstrual cycle (a rare form of chronic urticaria flares up seven to 10 days before your period)
• Physical trigger (cold, exercise, heat, sunlight)
• Recent infections (common cold, gastrointestinal bug)
• Work exposures (chemicals)

You may want to log this information and bring it to your office visit.

What you think are hives may actually be something else. Your doctor may be able to tell the difference between different skin conditions during a physical exam. For example, scabies, an infection caused by a mite that gets under the skin, can cause itching and raised red spots too. Unlike hives, however, scabies bites tend to localize at skin folds, i.e., between fingers, at the flexion points over your wrists, elbows, and knees, and along the genitalia. Even the dry inflamed skin in eczema can sometimes form blisters that can be confused for hives. Based on the appearance of your skin, your doctor will decide whether to pursue tests for those conditions.

Unless you have hives at the time you see your doctor, your physical exam is often not going to help make a diagnosis. That is the case unless you have dermatographism.

Dermatographism is a clinical sign associated with physical urticaria (hives that are caused by physical exposures) and atopic dermatitis. If you have dermatographism, a wheal forms when your skin is rubbed or stroked in a certain area. Your doctor will provoke this response by stroking your skin with a clean, firm object. A wheal will appear within six to seven minutes and start to fade 15 to 30 minutes later.

Lab tests are not always needed to diagnose urticaria. They are more helpful if you have certain symptoms or triggers.

Food Allergies

Food allergies do not only increase your risk for hives. They can also cause angioedema or in the worst case scenario, anaphylaxis. It is important to avoid exposures to foods that could trigger a life-threatening reaction.

Your doctor may order one of the following tests if he or she suspects a food allergy:

• Skin prick tests: A small amount of an antigen is scratched into the skin with a needle and you are monitored for a local reaction. If a test is positive, you will develop a small red pump over the area, usually within 20 to 30 minutes. This test is performed in your doctor's office in case you have a severe reaction that requires treatment. To get more accurate results, it is important not to take any antihistamines a week before your test.
• Enzyme-linked immunosorbent assay (ELISA): An increase in IgE antibodies is a hallmark of allergies. In an ELISA test, your blood is drawn and an antigen from a specific food is added to the sample. If you are allergic to that food, IgE antibodies against those antigens will be present (they will bond together in the blood sample and you will get a positive test result). The test is easily performed in a laboratory and is relatively inexpensive. It is also an excellent option for someone who is unable to tolerate a skin prick test.
• Radioallergosorbent test (RAST): The RAST also measures IgE antibodies by adding a specific allergen to a blood sample. While it may be used, ELISA tests have mostly replaced this option.

These tests can also be used to screen for allergies to other triggers, not just food.

Autoimmune Disease

As many as 40 percent to 45 percent of chronic urticaria cases are associated with autoimmune diseases like celiac disease, lupus, Sjögren’s syndrome, rheumatoid arthritis, and type 1 diabetes. It is even more strongly associated with autoimmune thyroid diseases like Graves' disease and Hashimoto's thyroiditis, which accounts for at least 10 percent of those cases.

If your doctor suspects an autoimmune condition, he or she may screen you by using some of the following blood tests:

• Antinuclear antibody (ANA)
• C-reactive protein
• Sedimentation rate
• Thyroid stimulating hormone (TSH)

Abnormal findings on these tests could lead to other more specific tests based on the suspected condition: transglutaminase antibodies for celiac disease; anti-dsDNA, anti-Smith, and complement for lupus; anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor for rheumatoid arthritis; and anti-SSA/Ro or anti-SSB/La for Sjögren’s syndrome.

It is usually not enough to check thyroid function alone. In 8 percent of cases, chronic urticaria is attributable to autoimmune thyroid disease but thyroid function is normal. For this reason, your doctor may also check for the presence of thyroid antibodies, specifically thyroglobulin antibody (anti-Tg) and thyroid peroxidase antibody (anti-TPO).

Infection

Numerous studies have shown that urticaria can be associated with infections from bacteria, viruses, and parasites. Infections may cause acute or chronic urticaria. Some viral infections in children, but not adults, have an increased risk of acute hives. These viruses include adenovirus, enterovirus, rotavirus, and RSV.

Most Common Infectious Causes of Urticaria:

(a) = acute, (c) = chronic

• H. pylori (c)
• Plasmodium (a)
• Staphylococcus (a) (c)
• Streptococcus (a) (c)
• Yersinia (c)