Allergy testing

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Definition

Allergy tests are any of several tests used to determine the substances to which a person is allergic.

Alternative Names

Patch tests - allergy; Scratch tests - allergy; Skin tests - allergy; RAST test

Why the Allergy testing is Performed

Allergy tests are used to determine the specific substances that cause an allergic reaction in an individual.

They may also be used to determine if a group of symptoms is a true allergic reaction, which involves antibodies and histamine release. Some food intolerances, in which there is an inability to digest a food because of lack of appropriate enzymes, produce symptoms similar to allergies. Some drugs, such as aspirin, can cause allergy-like symptoms without the formation of antibodies or the release of histamine.

Additional conditions under which the test may be performed:

• Allergic rhinitis
• Angioedema
• Contact dermatitis
• Nasal obstruction

Read more - What Allergy testing results mean, normal result of Allergy testing.

Dust mite picture

Dust mite picture, home dust mites - The house dust mite (sometimes abbreviated by allergists to HDM), is a cosmopolitan guest in human habitation. Dust mites feed on organic detritus such as flakes of shed human skin and flourish in the stable environment of dwellings. In nature they are killed by micro-predators and by exposure to direct sun rays. Dust mites are considered to be the most common cause of asthma and allergic symptoms worldwide.

House dust allergy: ventilate in winter

People who are allergic to house dust should make sure their bedrooms are well ventilated in winter, says a German professor.

Heating homes in the cold winter months provides an ideal climate for dust mites to breed, according to Professor Thomas Fuchs of Germany's Professional Association of Allergists.

Lower temperatures and lower humidity levels in a home can reduce the mites' survival rate. It's also a good idea to remove any items that attract dust.

People with dust allergies often treat the symptoms with antihistamines. According to Germany's Association of Pharmacists most antihistamines can be bought over the counter without a doctor's prescription.

"But despite that, you should not take them without getting the advice of a doctor first," warns Fuchs. It's also important to conduct an allergy test before beginning treatment.

Antihistamines help in the short term but become less effective over time. Patients should only take antihistamines as part of a transition phase to the beginning of hypo-sensitisation.

Hypo-sensitisation is a form of therapy whereby the patient is gradually exposed to higher doses of the substance that causes the allergy.

Fuchs says hypo-sensitisation is the best form of treatment in the long term.

Resource

Dust mites, allergy...

House dust mites - Mite allergy?

Asthma and all-year allergy in the nose are so common, that we accept them as 'one of those things', particularly when the doctor tells us just to keep taking the medicine and not to bother about finding out whether an allergy could be the cause. But what if you could find out the cause? Could you do something about it and reduce or end your dependence on medicines?

The answer is not an easy one, but we think it is important for you if your asthma or nose allergy is caused by allergy.

Infantile eczema or its equivalent in older children and adults may get better in some cases through avoiding mites and their dust. There is other evidence that mites may be involved in causing it. In some people, especially younger children, food allergy may wholly or partly cause eczema. But we don't know as much about this area as we would like.

Dust mites pictures

Over 90% of allergic individuals are allergic to dust mite allergens.

House dust is a mixture of various waste material like dead human skin cells, animal dander, fabric fibres, dust mites, bacteria, cockroach parts, mould spores, food particles and other debris. Of these, dead skin cells account for up to 80% of house dust. However, it is the house dust mite allergen that is the most common contributor to allergic asthma, allergic rhinitis and atopic eczema.

Generally, if doctors say that patients are allergic to house dust, they usually refer to the house dust mite. Of course, patients could also be allergic to other elements of house dust, such as cockroach parts, animal dander, mould and so on.

Home Dust mites pictures

Dust mites pictures

Dust Mites history

The inventor of the microscope, Anton van Leeuwenhoek, reported in 1694 that mites live in dust. Now, more than 300 years later, it is an established fact that dust mites can be found in house dust all over the world. Dust mites are not insects but are more closely related to spiders and ticks. There are two common dust mites, the American house dust mite (Dermatophagoides farinae) and the European house dust mite (D. pteronyssinus). Due to their very small size, these dust mites are not visible to the naked eye. They live in bedding, couches, carpet, stuffed toys and old clothing. Dust mites feed on the dead skin that falls off the bodies of humans and animals and on other organic material found where they live.

Though these mites live in many homes, only people who are allergic to them know they are there. Dust mites are second only to pollen in causing allergic reactions. When dust mites grow, they shed their skin. The shed skin and feces are what cause allergic reactions in people. Allergic reactions range from itchy noses and eyes to severe asthma attacks.

HABITS AND HABITATS

Dust mites do not live in air ducts in homes. Many people spend much time and money cleaning the air ducts to reduce dust mites. This is not necessary because dust mites need about 70 percent relative humidity or higher to live, and they need food. Areas where people spend much time, like a bed or a favorite plush chair, are prime sites for dust mites. The top part of mattresses containing fibrous material is a favorite place for dust mites during warm and humid times. The deeper parts of mattresses may provide protected areas for the dust mites during unfavorable conditions. Clothing is used by dust mites as a means of transportation from room to room or even from house to house.

CONTROL

Control of dust mites can be difficult, time-consuming and expensive. For people who are extremely sensitive, the following measures should be taken:

• Enclose mattresses, box springs and pillows in zippered allergen- and dust-proof covers.
• Wash bedding materials, including pillow cases, sheets, blankets and mattress pads every other week in hot water (130 °F).
• Eliminate or reduce fabric wall hangings such as tapestries or pennants.
• Purchase stuffed toys that are machine washable.
• Avoid using curtains, drapes or blinds on windows. Use plastic shades instead.
• Remove carpeting from the bedroom of the allergic person and replace it with tile or wooden floors.
• Replace upholstered furniture with wooden or plastic furniture.
• Vacuum often with a vacuum cleaner provided with a high efficiency purifying air (HEPA) filtration system. Throw away vacuum bags after use because dust mites can leave the bag.

Installing HEPA filters on air conditioner or heater vents is not practical or necessary, and may actually increase mite problems. Remember, dust mites cannot survive on the dust in the ducts, and the small holes of the filters will force air out of vents at a higher velocity, stirring up more dust than without filters.

Complete elimination of dust mites is unlikely. Reducing populations is the only likely way to reduce allergens in the air. Reducing humidity in the home by using a dehumidifier may help reduce populations, but reducing humidity levels in microclimates, such as in bed fibers or carpet fibers, is impossible. Chemical control is not necessary, nor will it have a lasting effect on dust mite populations. Regular cleaning and vacuuming will have a greater impact.

Detection of Dust mites

House dust mite presence is often suspected before they are actually seen and accurately identified. Requests for control often come from individuals who have been diagnosed by medical personnel as allergic to the house dust mite or the allergens produced.

The presence of house dust mites can be confirmed microscopically which requires collecting samples from mattresses, couches or carpets. Also, it requires the use of a microscope with sufficient magnification and the technical ability to recognize house dust mites under the microscope. In general practice, testing is unnecessary. dustmites are extremely common in household environments. They virtually always show up in a test, so testing just adds expense. A better question than "are dust mites present?" is "How can I control or remove them?"

Biology and Life Cycle of Dust mites

Adult females lay up to 40 to 80 eggs singly or in small groups of three to five. After eggs hatch, a six-legged larva emerges. After the first molt, an eight-legged nymph appears. After two nymphal stages occur, an eight-legged adult emerges. The life cycle from egg to adult is about one month with the adult living an additional one to three months.

The diet is varied with the primary food source, consisting of dander (skin scales) from humans and animals. However, needed nutrients can be provided from fish food flakes, pet food, fungi, cereals, crumbs, etc. Many mite species live in bird's nests, in barns, among stored grain, straw, etc.

House dust mites are cosmopolitan in distribution with much of the research previously done in Europe.

One of the major limiting factors in mite survival and population development is the availability of water for sorption. Highest mite densities occur in the humid summer months and lowest in drier winter periods. Dust mite populations are highest in humid regions and lowest in areas of high altitude and/or dry climates.

Due to the large quantity of skin scales sloughed off daily by humans, mites have an abundant food supply. Dust mite antigen levels are measured in bed dust, floor dust, and room air samples. Detection in room air was best during cleaning and bed-making activities.

Identification of Dust mites

House dust mites, due to their very small size (250 to 300 microns in length) and translucent bodies, are not visible to the unaided eye. For accurate identification, one needs at least 10X magnification. The adult mite's cuticle (covering) has simple striations that can be seen from both the dorsal (top) view and from the ventral (bottom) view. The ventral view of the house dust mite reveals long setae (hairs) extending from the outer margins of the body and shorter setae on the rest of the body. Through the microscope, one will see many oval-shaped mites scuttling around and over one another. There are eight hairy legs, no eyes, no antennae, a mouthpart group in front of the body (resembles head) and a tough, translucent shell, giving a "fearsome appearance."

Dust mites picture

Where do they live?

Beds are a prime habitat (where 1/3 of life occurs). A typical used mattress may have anywhere from 100,000 to 10 million mites inside. (Ten percent of the weight of a two year old pillow can be composed of dead mites and their droppings.) Mites prefer warm, moist surroundings such as the inside of a mattress when someone is on it. A favorite food is dander (both human and animal skin flakes). Humans shed about 1/5 ounce of dander (dead skin) each week. About 80 percent of the material seen floating in a sunbeam is actually skin flakes. Also, bedroom carpeting and household upholstery support high mite populations.

What are dust mites?

House dust mites are microscope bugs that primarily live on dead skin cells regularly shed from humans and their animal pets. Skin cells and scales, commonly called dander, are often concentrated in lounging areas, mattresses, frequently used furniture and associated carpeted areas, may harbor large numbers of these microscopic mites. A typical mattress can contain tens of thousands of dust mites. Sick yet? Nearly 100,000 mites can live in one square yard of carpet. Ready to convince your spouse to start bathing regularly? Did you know a single dust mite produces about 20 waste droppings each day, each containing a protein to which many people are allergic. Yuck! The proteins in that combination of feces and skin sheddings are what cause allergic reactions in humans. Depending on the person and exposure, reactions can range from itchy eyes to asthma attacks. And finally, unlike other types of mites, house dust mites are not parasites, since they only eat dead tissue. Gross, but true.