Hives - Diagnosing urticaria

Short-term urticaria can be diagnosed by examining the distinctive red rash.

If you have severe or persistent urticaria, you may need to have a number of tests to try and identify the underlying cause (see below).

Short-term urticaria

Your GP will usually be able to diagnose short-term (acute) urticaria by examining the rash on your skin.

They will want to find out what triggered your symptoms so you can avoid it in the future. The type of things they may ask you include:

when and where the rash began
what you had to eat just before it began and details of your usual diet
if you started taking any new medication just before your symptoms began
if you live or work in an environment where you come into contact with possible triggers, such as pets, chemicals or latex gloves
if you were stung or bitten by an insect just before your symptoms started
the current state of your health and if you've had any recent infections
if you've recently travelled to a foreign country and if so, where
if there's a history of urticaria in your family

In around half of all cases of acute urticaria, a cause can't be identified.

If your GP thinks that your symptoms are caused by an allergic reaction, you may have to go to an allergy clinic.

Tests may be carried out on either your skin or your blood to find out if you're allergic to suspected triggers for urticaria, such as foods and latex.

Long-term urticaria

If you have urticaria that lasts for more than six weeks, it's very unlikely that it's causd by an allergy, so allergy tests aren't usually recommended.

However, your GP should ask about anything that makes your urticaria worse, such as medicines, your alcohol and caffeine consumption, and stress levels.

You may also be referred for a number of tests to find out if there's an underlying cause of your chronic urticaria. These tests may include:

a full blood count test, which can identify anaemia
tests to determine the levels of antibodies in your blood
a stool sample, which can identify intestinal parasites
an erythrocyte sedimentation rate (ESR) test, which can help identify problems with your immune system
thyroid function tests, which can be used to check for an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism)
liver function tests, which can be used to check if you have any problems with your liver