Allergies Explained - go back to home page Allergies

Grass pollen discharging granules on exposure to water - picture by Dr H Morrow Brown

Dust Mite - picture by Dr H Morrow Brown

Dr H Morrow Brown MD
General Medical Council Registered Specialist
for Allergy and Respiratory Medicine


Tests for Allergies

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It may help in understanding allergies to describe how a case would be investigated in depth and in detail. The most important part of an allergy investigation is taking a very detailed case history, always including the family history, because if many family members also have allergies then the patient’s problems are also more likely to be due to allergy. Taking an allergic case-history properly is very interactive and time-consuming, depends on the experience and knowledge of the investigator, and is an example where art of medicine still takes precedence over science.

Mold sporesAn experienced Allergist will know the correct questions to ask and how to elicit detect significant clues in the patient’s answers which may suggest the most likely causes. For example, if hay fever or asthma is limited to June and July grass pollen is certainly the cause, but if it begins in the spring tree pollens are also involved. Symptoms continuing into the autumn, or becoming worse in damp weather, suggest that seasonal mould spores are also involved. Symptoms all year round suggest an allergen constantly present in the environment.

Observant patients may have noticed important circumstantial evidence relating to their sufferings, but may not mention their experiences unless asked directly by the allergist because they do not realise that their observations are important. For this reason an experienced allergist will ask essential leading questions which are always asked again later to check for consistency.

Using a Peak Flow meterSometimes the cause of the problem is in the working environment. For example if the patient is better at weekends, gets worse during the week, improves on holiday, and relapses promptly on return to work, an occupational cause is likely.

Blowing a Peak Flow Meter several times a day can sometimes produce evidence supporting an occupational cause. If the cause is in the home environment the patient should be better at work than at home, and better on holiday away from home, especially in a sunny climate, only to relapse on return home, often by the next morning.

The above comments refer mainly to asthma or rhinitis, but in other complaints such as migraine, eczema, irritable bowel, ulcerative colitis, nasal polyps, rheumatoid arthritis, behaviour problems in children, etc there may or may not be clues in the history suggesting that a daily food might be the cause. In eczema, especially in children, both foods and environmental allergens such as dust mites or pets may be involved, so all the allergens involved have to be avoided simultaneously to obtain relief from symptoms.

Sometimes sufferers observe that their problems improve when they are unable to eat due to a stomach upset or diarrhoea, only to recur when they start to eat again. This can be an important observation, but the reluctance of many medical colleagues to accept the possibility that food can cause many illnesses is difficult to understand.

Skin testing

Prick skin testing is a simple, safe, and almost painless way to test for allergies. Skin testing can be carried out in babies, and it is a common medical fallacy, even amongst paediatricians, that skin tests cannot be done until five or six years of age. Prick tests are performed by placing drops of extracts of the most likely causes of the allergy on the skin of the forearm or sometimes the back. The drops of test extract are then pricked through. using my specially made sterile standardised disposable plastic needles as illustrated. The prick tests are almost painless, and do not cause bleeding because the point is just the right length to reach the living cells of the skin and no further. As the needles are identical the tests are also standardised so that one reaction can be compared with another.

I invented these special testing needles many years ago, and although very seldom used in this country they are popular in Europe, USA, and Canada, Any positive reactions, which resemble an itchy insect bite, will appear in ten minutes, and indicate the likely causes of the allergy. In the UK, steel disposable prickers are most often used, but are very similar.

Morrow Brown Test Needle Cat & Dog Cod, Tuna, Salmon Peanut & Egg


The meaning of skin test reactions

Part of an allergy kit for skin testsUnfortunately, the interpretation of the results of prick skin testing is not straightforward, because many people have latent allergy (‘atopy’) which is not causing any symptoms but can produce meaningless false positive skin reactions. Although it is very convenient for the allergist that the skin all over the body becomes specifically sensitised to allergens, this can also be confusing when the prick test is positive but there is no history of reacting to the allergen.

Skin test reactions cannot be taken at their face value, and their significance depends on the case history and the experience of the allergist in deciding which are the most likely possibilities. Sometimes a test extract is not available, but can sometimes be improvised by first sticking the needle into the suspected fruit, or vegetable, such as an apple or a potato, and then into the skin of the patient using the same needle, so that a tiny trace of the juice is inserted into the skin.

Some testing extracts are more reliable and more potent than others, and sometimes the process of making the testing extracts destroys the allergen so it does not produce a reaction when it should.. For example many tests for foods are useless for this reason, but egg, fish, shellfish, lupin flour, and peanuts are reliable. Skin tests for milk and milk proteins, and for wheat, are only sometimes positive. Thus, although skin testing is simple, interpreting the results can be difficult and requires much experience.

Special Tests for Environmental Possibilities

For many years I have provided a unique service by using the patients own house dust or pet hairs to make instant extracts for skin testing against their own environment. When the hair of a family pet is used in this way and the result is a dramatic positive it is much easier to convince the patient that a good home should be found for the pet! This direct and very specific approach, not available anywhere else as far as I am aware, can demonstrate clearly and obviously if the cause of the allergy is in the home environment. The major source of dust mites in the home can also be pin-pointed.

A good example of how helpful these tests can be is the case of Susan who was twenty-nine when she bought an old house about 100 years old with second hand furniture, including a three piece suite and the bed, and the old carpets. From about six weeks after moving in she developed a rash on the arms, which became gradually worse over the winter, and after wall-papering.

The eczema spread to involve the whole body by one year, more or less controlled by steroid creams prescribed by the University Hospital Dermatology Clinic.

During the next year she became worse despite lavish application of steroid creams and Oilatum baths, etc and was so itchy that she could not resist scratching, slept badly, and dreaded going to bed.

Painting her bedroom precipitated a flare-up of her eczema so severe that she was admitted to hospital for ten days.. She requested allergy testing, but only patch tests were carried out, which were all negative, and RAST blood test which showed only a slight positive for cat, but ”not enough to justify getting rid of the cats”. She continued under the care of the skin clinic, living in her old house with the two cats for the next year, when she decided to put her cats in a cattery and live with her parents who had had a new house, but a dog and a cat.

She improved rapidly in this environment, suggesting that the old house was the cause, so she requested referral for allergy investigation. I found that she had negative skin reactions to dust mites, but was very positive to dust from the bed and the sofa, as shown.. There were also reactions to cat, dog, and horse, all of which she could tolerate without trouble. She remained well at her parents new house with the cat and the dog, sold the old house, and bought a new modern house in which she remains free from eczema but living with two cats.

Blood tests

  • Blood samples in test-tubesScientific blood tests (RAST) have been developed to help in these dilemmas, but are not always helpful either!! Positive skin tests mean that cells of the skin are sensitised, and that an antibody called specific IgE is present in the blood of that particular patient. The amount of this specific antibody in the blood as measured by RAST, usually reported as six grades of positive, will give some idea of the importance of IgE antibody in causing the symptoms.

  • Measuring the total of all the IgE allergy antibodies ( The Total IgE ) in the blood may also help, but can be disappointing and confusing. For example in eczema huge amounts of IgE antibodies are often present without any indication of which specific IgE antibodies are important. The Total IgE in asthma may also be high, with varying amounts of specific IgE to common allergens such as pollen, dust mite, and pets. The amount present will suggest the importance of each allergen in conjunction with the case-history, and give useful information helpful in the management of the case. However a Total IgE reading within normal limits does not exclude allergy, as is sometimes thought, because it may conceal quite a high positive test for specific IgE directed towards one specific allergen which has not been tested for.

  • When the skin tests are all negative we cannot go further, unless the most likely allergens are suggested by the history, for which testing extracts may not be available. If the Total IgE is very high, without any skin test reactions or history to suggest what the important allergen may be, a specific daily food for which no test is available is a possibility. Sometimes the story will suggest which specific food may the cause, and pricking some of the food or juice into the skin produces a confirmatory reaction, as in the case of allergy to lupin flour described on another page.

It is obvious that if the cause of an allergic problem can be identified and avoided a ‘cure’ is possible. Unfortunately this is not easy, because even if the trigger is found it may one which is impossible to avoid. At present there are there are laboratories claiming that they can to find the cause of your allergy from a drop of your blood, but the significance of the results is doubtful because these tests have not been subjected to acceptable scientific trials. Many complementary treatments are advertised which have never been proved to be either significant or effective, so you have been warned.. There is no quick fix.

Cytology tests (Microscopic examination of cells from the patient)

In 1958 I discovered that if microscopic examination of the sputum from an asthmatic patient revealed many eosinophil cells typical of an allergic reaction, I could confidently predict that oral steroids would be dramatically effective. Although this test indicates the most effective treatment, it does not identify the cause. When these eosinophil cells are not present oral steroids are unlikely to be very helpful. This finding became even more important in 1970, when this same test enabled me to select proven allergic asthmatics for the first successful clinical trials of Becotide, the very first steroid aerosol. Trials elsewhere had shown the aerosol to be ineffective, and the makers were on the point of discarding it as useless, but. trials in Derby showed that in proven asthmatics the aerosol was very effective indeed, so the manufacturers decided to give the drug another chance. Before long inhaled steroids were used world-wide, and this treatment acknowledged as the most important advance in asthma therapy in the last 30 years because inhaled steroids control most asthmatics without the long-term side-effects caused by oral steroids.

Examination of a smear of the nasal mucus is equally helpful in chronic rhinitis to decide if it is allergic or not and whether nasal steroid sprays will help. Cytological examinations carried out during a consultation enable correct decisions regarding the most appropriate treatment to be made on the spot, regardless of the presence or absence of skin test reactions. I am not aware of anyone else in Britain who does this investigation right there in the consulting room.

Macrophages in bronchitis Eosinophils in allergic asthma or rhinitis

This patient is unique. His response to steroids changed many times over the years,
according to whether eosinophils were present or not


Bronchial and Nasal Provocation Tests

A bronchial provocation test is a carefully controlled exposure by inhaling an aerosol of a dilute solution of the suspect allergen. This will produce a slight attack of asthma if the allergen used is the cause. Many years ago I devised a method of carrying out this test safely, and in such a way that an answer was obtained without causing a severe attack of asthma. Nasal provocation tests can also be done to find the cause of chronic rhinitis by placing a drop of test extract in the nostril..

Child sneezing into handkerchiefBefore 1986 this procedure was routinely used in my clinic order to prove the cause of the asthma, and to prove that desensitising injections, (referred to today as immunotherapy) were necessary. After a course of desensitising injections containing this allergen in gradually increasing amounts had been completed another provocation test would be carried out to show if the treatment had made the patient immune to the allergen or not. If still positive further injections were given until the provocation test became negative. This regime was very successful in many asthmatics, with lasting results which will be shown elsewhere in this website, but only as a matter of interest..

Today it is unreasonable to subject a patient to a provocation test to prove the cause of their asthma because, since 1986, we cannot follow up a positive reaction with injection treatment to desensitise them against the allergen involved. The only justification for a provocation test nowadays would be to confirm that the cause was something which could be totally avoided or removed.

An over-reaction by the Committee for Safety of Medicines in 1986 is still preventing the effective treatment of inhalant allergies in this country. Timidity rules OK today, so we have to practise defensive medicine, watch our backs, and deprive our patients of potentially curative treatment.! Desensitisation by using drops taken daily under the tongue by the patient at home instead of injections has been shown repeatedly in Europe and elsewhere to be safe, and is now permitted in the UK, but the NHS nearly always refuse to pay for this treatment. Details of my successful unpublished trial of sub-lingual treatment twenty years ago are given elsewhere in this website.

Challenge Tests for Food Allergies

Skin tests and blood tests for foods are often unreliable, so the only test which really proves a food allergy is to eat it and observe what happens. When the patient is allergic to a food great care is necessary because a tiny amount may trigger off a serious reaction, so never do a test yourself if there is an question of an allergy to a food because it can be dangerous.

For example after avoiding peanuts with great care for years it may be questioned if the allergy has subsided, but a deliberate challenge by feeding a small amount is the only way to be certain. Food challenge for foods such as peanut must always be carried out in hospital with emergency equipment at hand in case of a serious reaction. Challenge tests may also be carried out double blind to prove beyond all doubt if it is still necessary to avoid peanut or other potent allergens with great care.

Challenge Tests for Diagnosis of Food Intolerance

Various foods which can casue allergic responsesPatients suffering from food intolerance are quite different because normal amounts of food are needed to cause a reaction which is often delayed by up to 24 hours, sometimes even longer. Challenge tests can be done at home because the effects are not so severe, sudden, or potentially dangerous as in food allergy, but should be carried out only when asked to do so. Challenge tests using suspect foods are very necessary, but usually carried out only after removal of the main possibilities from an elimination diet has brought about obvious improvement Obviously if there is only a short interval between eating the food and the onset of the effects, and it happens every time, that food must be avoided completely.

Ideally, food tests should be double blind, but being given the offending food by mistake, or in a restaurant, can be very convincing. In clinical practice open testing for food intolerance is the only practical method, but with the cooperation of a partner a single blind test is possible. Whatever method is used it is important to demonstrate that the same amount of food causes the same effect after the same time interval, preferentially on three occasions.

A food diaryDemonstrable repeatability is necessary because it is so easy to jump to conclusions and end up with a restricted diet for no good reason. To discover the causes and avoid them has the potential to improve quality of life and greatly reduce the need for medication.

A careful food diary which notes everything that passes the lips, including medicines, vitamins, supplements, sweets, and even toothpaste, is an essential part of tracking down the causes of a problem, whatever it may be.

Only in this way is it possible to spot a delayed reaction to something eaten the day before. If the cause is a daily food it is obvious that symptoms should be fairly constant, and that only by using elimination diets will it be possible to make sense of the problem.


"It is a paradox that while Britain has the highest incidence of allergic disease in the world, it also has the most inadequate allergy service"

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