How to Diagnose Urticaria and Hives

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.

Medical History

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.

Physical Exam

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.

Labs and Tests

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
  Bacteria Parasites Viruses
  H. pylori (c)
- Plasmodium (a)
- Staphylococcus (a) (c)
- Streptococcus (a) (c)
- Yersinia (c)

**Most Common Infectious Causes of Urticaria**. *(a) = acute, (c) = chronic*
Bacteria	Parasites	Viruses
H. pylori (c)

Anisakis (a)
Blastocytsis (a) (c)
Giardia (a)
Strongyloides (c)
Toxocara (c)

Cytomegalovirus (a) (c)
Epstein-Barr (a) (c)
Hepatitis A or B (a)
Hepatitis C (c)
Influenza (a)
Parvovirus B19 (a)

Thankfully, most viral infections and related hives are self-limited. Chronic infections, however, may lead to chronic urticaria and require treatment. Lab tests may be necessary to make a diagnosis.

Lab screening often begins with a complete blood count. A high white blood count could be a sign of infection and an increase in eosinophils, in particular, could indicate that a parasitic infection is to blame. In this case, a stool specimen is usually collected to screen for ova and parasites.

Serology measures antibodies in the body against certain pathogens, indicating that you have been infected or at least exposed to that organism. There are serologic blood tests available for many of the bacteria and viruses listed above. Anti-streptolysin (ASO) checks for antibodies against Streptococcus.
H. pylori can be tested for with serology, but there are two other ways to screen for it that may be more accurate.
- Stool antigen test: H. pylori lives in the stomach. Antigens from the bacteria are excreted into the stool and can be detected in a stool sample using an immunoassay.
Urea breath test: H. pylori breaks urea down into carbon dioxide and ammonia. After you ingest a urea tablet or liquid that has trace amounts of a radioactive carbon attached, you are asked to breathe into a container. The test detects H. pylori based on the presence of carbon isotope in your exhalation.

Physical Causes

Physical urticaria accounts for 20 to 30 percent of all chronic urticaria. In this case, exposure to a certain environmental trigger can cause hives to form.

To make a diagnosis, your doctor may want to mimic the physical stimulus in a controlled environment. He may also try to establish how much of that stimulus you can tolerate before developing symptoms. This will allow him to provide practical advice on how to minimize and manage symptoms.
These are the most common physicals triggers your doctor could test for based on your history:
- Cold: Cold urticaria is a condition where cold air, liquids, or objects cause hives. Your doctor may perform the ice cube test, where an ice cube in a plastic bag is applied to the forearm for about five minutes. A reaction usually occurs within 10 minutes of removal.
Exercise: Some people develop hives with exercise. This could be from the increased core body temperature that occurs with exercise, also referred to as cholinergic urticaria. It could also occur when you are active shortly after being exposed to a food trigger. Your doctor may have you exercise on a stationary bicycle or on a treadmill to induce symptoms.

Heat: Local heat can sometimes cause wheals to form. Heat provocation testing is performed by putting a glass or metal cylinder filled with water above 110 degrees against the arm for five minutes. Hives develop within several minutes.
Pressure: There is a form of delayed dermatographism where swelling of the skin occurs four to six hours after pressure is applied, although it can occur anywhere from 30 minutes to 12 hours afterward. It can happen anywhere on the body where clothes are tight, on the buttocks with prolonged sitting, or on the feet after extended walking. A doctor may apply a 10-pound weight to your arm for 20 minutes. You will be asked to monitor for a skin reaction over the next 24 hours.
Sunlight: Solar urticaria is rare and develops on uncovered skin within minutes of exposure to direct sunlight. Provocation testing is carried out by exposing small defined areas of the skin to ultraviolet (UV) lamps with UV-A and UV-B filters.

Testing is most accurate if you are not on antihistamine therapy at the time.

Skin Biopsy

Skin biopsy is rarely needed, but it can be helpful if there is a concern for urticarial vasculitis. This is not actually a form of urticaria but can mimic it in appearance. A difference is that skin lesions are often described as burning rather than itchy.
This condition is much more serious than classic hives because it can affect multiple organ systems, including the gastrointestinal tract, kidneys, lungs, and muscles.
Differential Diagnoses
Hives have a variety of causes, ranging from allergies to autoimmune disease. Cold or hot temperatures, exercise, sunlight, and even tight clothes can cause a flare-up. Chronic infections, like H . pylori or hepatitis C, have also been associated with urticaria.
Keep in mind that not everything that looks like a hive is a hive. Rashes can be caused by fungi, viruses, and even parasites like scabies mites. In these cases, your doctor may choose to perform a culture or scrape a sample of your skin to look at it under the microscope. Conditions that inflame the skin, like eczema, can also cause local itching that can be mistaken for hives. Most importantly, it is critical to differentiate between true hives and urticarial vasculitis, which can look similar in appearance but can have serious complications. As discussed above, a skin biopsy may be appropriate in these cases.

Do not be surprised if your doctor starts you on a treatment right away based on your symptoms and physical exam. The majority of the time, your doctor will diagnose urticaria based on your history alone. When chronic urticaria is suspected, a more extensive evaluation may be pursued. If you have concerns about hives, reach out to your doctor for an exam.