This section will tell you about the tests that your doctor may do to decide whether or not you have an allergy to latex. It will also tell you about any risks in having the tests and how accurate they are.

In order to decide whether or not you are allergic to latex, the doctor will normally need to do two things:

1. Ask you about the times when you have had a reaction to consider whether these are likely to have been caused by latex allergy or something else instead. If the doctor thinks that latex allergy might be the cause, this is called a suggestive clinical history (see 'symptoms').

2. If there is a suggestive clinical history of latex allergy, the doctor will usually carry out tests to support this. These tests will show whether or not you have antibodies to latex (latex-specific IgE).

There are two different tests that can show this:

i) Latex-specific IgE blood test (sometimes called a RAST test)

• This test measures the amount of IgE in the blood that is specifically directed at latex.
• A small amount of blood is taken from a vein in your arm with a needle and syringe.
• This can be done at a hospital or GP surgery by a nurse or doctor.
• It might feel a bit uncomfortable but it shouldn’t hurt.
• If you would like more details about the latex-specific IgE blood test click here

ii) Skin prick test (SPT)

• This test is used to confirm that latex-specific IgE is attached to mast cells which are special cells in the skin involved in allergy.
• It is normally carried out in a hospital or surgery where there are nurses or doctors who have been specially trained in how to do the test.
• A small drop of liquid that contains latex allergen is placed onto your skin, usually on the inside of the forearm. Two drops of‘control’ liquid (positive and negative) are also placed on your skin. The position of all the drops are marked with a pen or tape.
• A tiny hole is then made in the skin at each drop using a lancet to allow the allergen and control test liquids into the body. This should only be slightly uncomfortable.
• If there is a positive reaction, you will get some itching, redness and a small weal at the test site, usually within 15 minutes. If there is no reaction to the test liquid, stronger doses may then be tested, in which case the testing may take up to an hour to perform.
• The control tests are:
  
  (i) Positive (histamine) to check that the immune system is able to react to the test. This should also produce some itching, redness and a small weal.
  (ii) Negative (saline or glycerine) to compare against the test substance reaction. This is necessary because, although most people will not have any reaction, a few will produce a reaction simply to the prick of the lancet, and this has to be taken into account when interpreting the test results.
  
  
• Positive reactions normally settle down after about half an hour.
• If you would like more details about the skin prick test click here
• For a picture of what a skin prick test looks like click here

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What happens if the results of these tests are negative?

If the results of these tests are negative but your clinical history still suggests that you may have latex allergy, your doctor may decide to carry out a glove challenge (provocation) test.

• Firstly, you will be asked to wear just the finger of a latex glove and also the finger of a vinyl glove as a control. The doctor will observe any reaction that occurs.
• If there is no reaction after 15 minutes, your doctor may then ask you to wear the whole glove. You will wear a vinyl glove on your other hand as a control.

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Are there any risks with doing these tests?

There is a very small risk with skin prick testing and glove challenge that carrying out these tests might produce a severe (anaphylactic) reaction. For this reason, these tests must only be performed by trained staff in a healthcare setting where oxygen, adrenaline and latex-free resuscitation equipment is available.

Some doctors may be unwilling to carry out these tests because of this risk.

There are also other circumstances where skin prick testing and glove challenge may not be carried. For example, if you:

• have had an anaphylactic reaction to latex in the past
• have unstable asthma (because the test could make this worse)
• have extensive eczema (which can make interpretation of patch tests difficult)
• need for antihistamine medication which cannot be stopped because of the severity of the symptoms (as this would influence the test reactions).

IgE blood testing does not carry these risks and is safe to perform.

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How accurate are these tests?

Skin prick testing is a more reliable test than IgE blood test. Both these tests are useful for doctors to support a clinical diagnosis of latex allergy, but they are not 100% accurate. Just occasionally, a latex-allergic individual may have negative test results, and if there is a strongly suggestive clinical history (see 'What are the symptoms?'), it is wise to err on the side of caution and avoid the main potential dangers (see 'Is it serious?').

If a person has a condition called dermographism and wears a tight-fitting glove, s/he may get itching and swelling of the skin on the hand which can look very like contact urticaria to latex (see 'symptoms'). People with this condition get weals when the skin suffers any minor injury or from the pressure of a belt or glove. For more information on dermographism click here

A suspected diagnosis of latex allergy should therefore be confirmed by a doctor who is experienced in carrying out the tests, interpreting the results and providing a management plan. (see 'How is latex allergy managed?') This is normally an allergist, clinical immunologist or dermatologist.

Further information

For a summary of all the tests described here click here.

For a more detailed review of diagnosis of latex allergy click here

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