Tests & Procedures


Asthma diagnosis is based on a number of things, including a physical exam, answers to questions about your symptoms and overall health, and results of lung tests or other tests.

Medical history

The first step in diagnosing asthma is talking to your doctor about your symptoms and your health. This can provide clues as to whether your symptoms are most likely caused by asthma or may be caused by something else. Your doctor will likely ask:

  • What are your exact symptoms? When do they occur, and does anything specific seem to trigger them?
  • Are you often exposed to tobacco smoke, chemical fumes, dust or other airborne irritants?
  • Do you have hay fever or another allergic condition?
  • Do you have any blood relatives with asthma, hay fever, or other allergies?
  • What health problems do you have?
  • What medications or herbal supplements do you take? (Many medications can trigger asthma.)
  • What is your occupation?
  • Do you have pet birds or raise pigeons? (In some people, exposure to birds can cause asthma-like symptoms.)
Physical exam

Your doctor may:

  • Examine your nose, throat and upper airways (upper respiratory tract).
  • Use a stethoscope to listen to your breathing. Wheezing — high-pitched whistling sounds when you breathe out — is one of the main signs of asthma.
  • Examine your skin for signs of allergic conditions such as eczema and hives.

Your doctor will want to know whether you have common signs and symptoms of asthma, such as:

  • Recurrent wheezing
  • Coughing
  • Trouble breathing
  • Chest tightness
  • Symptoms that occur or worsen at night
  • Symptoms that are triggered by cold air, exercise or exposure to allergens.
Asthma signs and symptoms in children

In children, additional signs and symptoms may signal asthma. These may include:

  • Breathing that is louder than normal or faster than normal. Newborns typically take 30 to 60 breaths a minute. Toddlers typically take 20 to 40 breaths a minute.
  • Frequent coughing or coughing that worsens after active play.
  • Coughing, clear mucus and a runny nose caused by hay fever.
  • Frequent missed school days.
  • Limited participation in physical activities.
Lung Tests

Lung tests (pulmonary function tests) such as spirometry are often used to help confirm an asthma diagnosis. These tests check how well your lungs are working. During spirometry, you take a deep breath and forcefully breathe out (exhale) into a tube connected to a machine called a spirometer. This records both the amount (volume) of air you breathe out and how quickly you can exhale. If certain key measurements are below normal for a person your age, it may be a sign that your airways are narrowed by asthma.

After taking lung test measurements, your doctor may ask you to inhale an asthma drug to open air passages. Then, you'll do the lung tests again. If your measurements improve significantly after taking the medication, you may have asthma.

Challenge test

With this test, your doctor tries to trigger asthma symptoms by having you inhale a substance that causes the airways to narrow in people with asthma, such as methacholine (meth-uh-KO-leen).

If you appear to have asthma triggered by exercise (exercise-induced asthma), you may be asked to do physical activity to see whether it triggers symptoms.

After taking action to trigger your symptoms, you'll retake the spirometry test. If your spirometry measurements are normal, you probably don't have asthma. But if your measurements have fallen significantly, it's possible you do.

Lung tests in children

Doctors seldom do lung tests in children under age 5. Instead, diagnosis is generally based on a child's signs and symptoms, medical history, and physical examination. It can be especially difficult to diagnose asthma in young children because there are many conditions that cause asthma-like symptoms in this age group.

If your child's doctor suspects asthma, the doctor may prescribe a bronchodilator — a drug that opens the airways. If your child's signs and symptoms improve after using the bronchodilator, your child may have asthma.

Exhaled nitric oxide test

With this test, you breathe into a tube connected to a machine that measures the amount of nitric oxide gas in your breath. Nitric oxide gas is produced by the body normally, but high levels in your breath can mean your airways are inflamed — a sign of asthma.

Additional tests: Ruling out conditions other than asthma

Depending on your age, your medical history and initial testing, your doctor may suspect that you have a condition other than asthma. Conditions that can cause asthma-like symptoms include:

  • Something blocking in the airways (airway obstruction). Breathing a piece of food or a small object into the airways is especially common in infants and young children.
  • Another lung disease such as emphysema or chronic obstructive pulmonary disease (COPD).
  • A tumor or tumors in the airways.
  • Bronchiolitis (BRONG-ke-oh-LIE-tis). This type of airway inflammation often stems from a viral lung infection such as respiratory syncytial (sin-SISH-ul) virus, particularly in children under 2.
  • Lung infection (pneumonia) caused by a bacteria or virus.
  • A blood clot in the lung (pulmonary embolism).
  • Heart failure (congestive heart failure).
  • Vocal cord dysfunction, which is also called paradoxical vocal cord movement or laryngeal dysfunction.

To rule out possible causes of your breathing problems, you may need tests such as:

  • Chest and sinus X-rays
  • Blood tests — for example, a complete blood count (CBC) test
  • Computerized tomography (CT) scans of the lungs
  • Gastroesophageal reflux assessment
  • Examination of the phlegm in your lungs (sputum induction and examination) for signs of a viral or bacterial infection.

Your doctor may also want to see whether you have any other conditions that often accompany asthma and can make symptoms worse. These include:

  • Heartburn (gastroesophageal reflux disease, or GERD)
  • Hay fever
  • Sinusitis

Your doctor may also perform allergy tests. These can be either skin tests or blood tests, or both. Allergy tests aren't specifically used to diagnose asthma. But, they can help identify an allergic condition, such as hay fever, that may be causing your symptoms or worsening existing asthma.

For some people, asthma diagnosis is straightforward. But for others, diagnosing the cause of breathing problems is a challenge. It can be difficult to differentiate asthma from other conditions — particularly in young children. When existing asthma is worsened by another condition, such as hay fever, it can further complicate diagnosis. Your doctor will need to piece together all of the information possible to determine what's causing your symptoms. Even if a diagnosis isn't certain, your doctor may prescribe medications or other treatment to see whether it helps.

Because numerous conditions can cause asthma-like symptoms, it may take some time — and patience — to get the correct diagnosis and determine the best course of treatment.
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When you visit an allergist, the doctor will:

  • Take a medical history. You will be asked about your health, your symptoms and whether members of your family have asthma or allergies such as hay fever, hives or skin rashes like eczema.
  • Ask you about your symptoms. The doctor will want to know when symptoms occur, how often they happen and what seems to bring them on. The allergist will also ask about your work, home and eating habits to see if these can provide clues to help pinpoint your allergy.
  • Do a physical exam.
  • Conduct allergy tests.

Tests can be done for common allergens such as plant pollens, molds, dust mites, animal dander, insect stings and various foods such as peanuts, eggs, wheat, shellfish and milk. Testing also is available for some medicines, such as penicillin. There are two types of skin tests:

  • The prick test pricks the surface of the skin with a tiny amount of the allergen. The test is done on your back or the inside of your arms with several allergens tested at once. If you're allergic, redness and swelling appear at the site of the prick.
  • The intradermal test injects the allergen with a very fine needle under the first few layers of the skin. This type of skin test may be used when the result of a prick test is not clear.
Allergy Blood Tests

Skin tests are more sensitive than blood tests, but an allergist might use a blood test to diagnose allergies if:

  • You're taking a medicine that could interfere with allergy test results.
  • You have very sensitive skin or a serious skin condition.
  • You had a previous reaction to an allergen that suggested you were very sensitive and should avoid more exposure.

After drawing blood, the sample is sent to a lab to look for the antibodies of specific allergens that show if you have allergies. It takes a few days to receive blood test results.

Skin Tests

Skin tests for allergic disorders have been around since the 1860s. Today, prick or puncture tests are commonly used by allergists as diagnostic aids. These tests are not very invasive and, for most allergens, they tend to produce quick results. If the results of prick or puncture tests are negative, they may be followed by intradermal tests, which give allergists more details about what’s causing the underlying symptoms.

Here is how both types of tests are administered:

  • Prick/puncture. A diluted allergen is applied with a prick or a puncture on the surface of the skin.
  • Intradermal. Using a 26- to 30-guage (very thin) needle, a diluted allergen is injected immediately below the skin surface.

After either type of test, the area of the skin is observed for about 15 minutes to see if a reaction develops. The “wheal”—a raised, red, itchy bump and surrounding “flare”—indicates the presence of the allergy antibody when the person is exposed to specific allergens. The larger the wheal and flare, the greater the sensitivity.Although skin testing may seem simple, it must be carried out by trained practitioners with an understanding of the variables and risks of the testing procedure.

Steps should include:

  • After reviewing the patient’s medical history and performing a physical exam, the allergist determines that allergy skin testing is both appropriate for the patient and does not put the patient at risk for a bad outcome (such as severe anaphylaxis or an asthma attack in poorly controlled asthma).
  • A trained nurse performs the skin testing under the supervision of the allergist.
  • The allergist personally “reads” the skin tests and, in evaluating the skin test reactions, discerns several factors that lead to proper interpretation.

These factors include:

  • Proper evaluation and selection of which patient may benefit from skin testing
  • Condition and reactivity of the skin
  • Proper selection of where the skin tests are placed
  • Type of skin test placed
  • Device used for skin testing
  • Proper technique in applying the tests
  • Quality and selection of the allergen extracts used
  • Medications that could alter the validity of the results
Reporting Standards

In addition to carefully considering allergy testing variables, board-certified allergists are trained to report test results according to standard practices endorsed by the American College of Allergy, Asthma & Immunology.

Standardized allergy test records are vital since patients often change doctors. When they do, their new allergist must be able to accurately interpret their health records. If information is incomplete, patients may be ordered to undergo additional skin testing that would have been unnecessary had standard practices been followed.

Guidelines suggest that skin test records report the diameter of the wheal and the surrounding “flare” (measured in millimeters) and record information to account for the differences in testing devices. The measurements are usually reported in millimeters of diameter.

Allergy nurses performing allergy and asthma tests are also required to meet basic quality assurance standards to ensure that they are using the proper techniques.

Seeing a board-certified allergist will assure these guidelines are followed. Allergy skin testing is relatively safe; adverse reactions are rare. Even so, researchers recommend that the value of any test be carefully considered before it is administered.

Potential Risks of Non-Specialist Care Include:

  • Misinterpretation of test results
  • Overdiagnosis
  • Mismanagement
  • Overprescription of medications and treatments
  • Costly and unnecessary allergen avoidance
Allergy Shots (Allergy Immunotherapy)

Immunotherapy is a preventive treatment for allergic reactions to substances such as grass pollens, house dust mites and bee venom. Immunotherapy involves giving gradually increasing doses of the substance, or allergen, to which the person is allergic. The incremental increases of the allergen cause the immune system to become less sensitive to the substance, probably by causing production of a "blocking" antibody, which reduces the symptoms of allergy when the substances is encountered in the future. Immunotherapy also reduces the inflammation that characterizes rhinitis and asthma.

Before starting treatment, the physician and patient identify trigger factors for allergy symptoms. Skin or sometimes blood tests are performed to confirm the specific allergens to which the person has antibodies. Immunotherapy is usually recommended only if the person seems to be selectively sensitive to several allergens.

How allergy immunotherapy is done

An extract of a small amount of the allergen is injected into the skin of the arm. An injection may be given once a week (sometimes more often) for about 30 weeks, after which injections can be administered every two weeks. Eventually, injections can be given every four weeks. The duration of therapy may be three to five years, sometimes longer.


There is a small danger of anaphylactic shock (a severe allergic reaction) shortly after an injection. Therefore, immunotherapy requires medical supervision.

Immunotherapy for asthma

Immunotherapy is effective in the treatment of allergic asthma. Allergy shots can help relieve the allergic reactions that trigger asthma episodes, thereby enhancing pulmonary function and decreasing the need for asthma medications.

No matter what type of allergy test is given, allergists are experts at selecting which allergens should be tested, reviewing the results, and helping you find the right treatment for relief.
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To diagnose COPD, your doctor will probably do the following tests:

  • Medical history and physical exam. These will give your doctor important information about your health.
  • Lung function tests. These measure the amount of air in your lungs and the speed at which air moves in and out. Spirometry is the most important of these tests.
  • Chest X-ray. This helps rule out other conditions with similar symptoms, such as lung cancer.
Tests done as needed
  • Arterial blood gas test. This test measures how much oxygen, carbon dioxide, and acid is in your blood. It helps your doctor decide whether you need oxygen treatment.
  • Oximetry. This test measures the oxygen saturation in the blood. It can be useful in finding out whether oxygen treatment is needed, but it provides less information than the arterial blood gas test.
  • Electrocardiogram (ECG, EKG) or echocardiogram. These tests may find certain heart problems that can cause shortness of breath.
  • Transfer factor for carbon monoxide. This test looks at whether your lungs have been damaged, and if so, how much damage there is and how bad your COPD might be.
Tests rarely done
  • A test to measure levels of alpha-1 antitrypsin, or ATT. ATT is a protein your body makes that helps protect the lungs. People whose bodies don't make enough ATT are more likely to get emphysema.
  • A CT scan. This gives doctors a detailed picture of the lungs.
Regular checkups

The best test for COPD is a lung function test called spirometry. This involves blowing out as hard as possible into a small machine that tests lung capacity. The results can be checked right away, and the test does not involve exercising, drawing blood, or exposure to radiation.

Because COPD is a disease that keeps getting worse, it is important to schedule regular checkups with your doctor. Checkups may include:

  • Spirometry.
  • Arterial blood gas test.
  • X-rays or ECGs.

Using a stethoscope to listen to the lungs can also be helpful. However, sometimes the lungs sound normal even when COPD is present.

Pictures of the lungs (such as x-rays and CT scans) can be helpful, but sometimes look normal even when a person has COPD (especially chest x-ray).

Sometimes patients need to have a blood test (called arterial blood gas) to measure the amounts of oxygen and carbon dioxide in the blood.

Tell your doctor about any changes in your symptoms and whether you have had any flare-ups. Your doctor may change your medicines based on your symptoms.

Early detection

The sooner COPD is diagnosed, the sooner you can take steps to slow down the disease and keep your quality of life for as long as possible. Screening tests help your doctor diagnose COPD early, before you have any symptoms.

Talk to your doctor about COPD screening if you:

  • Are a smoker or ex-smoker?
  • Have had serious asthma symptoms for a long time, which have not improved with treatment.
  • Have a family history of emphysema.
  • Have a job where you are exposed to a lot of chemicals or dust.

The U.S. Preventive Services Task Force (USPSTF) does not recommend COPD screening for adults who are not at high risk of developing COPD.
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Chronic Cough

Your medical history and physical examination help determine which tests your doctor will order. The goal of testing is to identify the underlying cause of your chronic cough.

Imaging tests
  • X-rays. Although a routine chest X-ray won't reveal the most common reasons for a cough — postnasal drip, acid reflux or asthma — it may be used to check for lung cancer and other lung diseases. An X-ray of your sinuses may reveal evidence of a sinus infection.
  • Computerized tomography (CT scan). A CT scan takes X-rays from many different angles and then combines them to form cross-sectional images. This technique can provide more-detailed views of your lungs, but it's not a routine exam in the initial evaluation of a chronic cough. CT scans may also be used to check your sinus cavities for pockets of infection.
Lung function tests

These simple, noninvasive tests measure how much air your lungs can hold and how fast you can exhale. Sometimes you may also have an asthma challenge test, which checks how well you can breathe before and after inhaling a drug called methacholine (Provocholine).

Lab tests

If the mucus that you cough up is discolored, your doctor may want you to test a sample of it for bacteria.

Scope tests

These tests use a thin, flexible tube equipped with a light and camera to visualize structures within your body. To evaluate possible causes of chronic cough, this equipment may be inserted into your:

  • Windpipe (trachea). This type of test, called a bronchoscopy, checks your bronchial tubes for signs of infection or obstruction.
  • Nostrils. The video camera can help your doctor assess the status of the nasal mucosa and the openings to your sinuses.
  • Esophagus. If your doctor suspects acid reflux is causing your chronic cough, he or she may want to examine the inside of your esophagus — the tube that connects your mouth to your stomach.

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Alpha-1 Antitrypsin Deficiency (AAT)

An alpha-1 antitrypsin level is ordered to help diagnose the cause of early onset emphysema, especially when a person does not have obvious risk factors such as smoking or exposure to lung irritants such as dust and fumes.

Alpha-1 antitrypsin is also ordered to help diagnose the cause of persistent jaundice and other signs of liver dysfunction. This is done primarily in infants and young children but may also be done in patients of any age.

Alpha-1 antitrypsin phenotype testing may be ordered if the alpha-1 antitrypsin concentration is lower than normal. It looks at the amount and type of AAT being produced and compares it to normal patterns.

DNA testing may be done as a follow-up to an alpha-1 antitrypsin level and phenotype. Once it has been established that an abnormality exists, then the DNA genetic testing can be ordered to establish which SERPINA1 gene alleles are present. This test does not test for every variant, just the most common ones - M, S, and Z, as well as any that may be common in a particular geographical area or family. Once the affected person’s SERPINA1 gene alleles have been determined, other family members may be tested to establish their own possible risk of developing emphysema and/or liver involvement as well as the likelihood that their children might inherit it?

Alpha-1 antitrypsin testing may be ordered when a newborn or infant has jaundice that lasts for more than a week or two, an enlarged spleen, ascites, pruritus, and other signs of liver injury. It may be ordered when a person under 40 years of age develops wheezing, a chronic cough or bronchitis, is short of breath after exertion and/or shows other signs of emphysema. This is especially true when the patient is not a smoker, has not been exposed to known lung irritants, and when the lung damage appears to be located low in the lungs. AAT testing may also be done when you have a close relative with alpha-1 antitrypsin deficiency. Alpha-1 antitrypsin phenotype testing is ordered when a patient has a decreased level of AAT. DNA testing is performed when the AAT test indicates that the patient has lower than normal level of AAT and when the alpha-1 antitrypsin phenotype test indicates that some or all of the AAT protein being produced appears to be a variant. It may also be ordered in the rare case when no AAT is being produced. AAT DNA testing may be done on close relatives when there is an affected family member and when a patient wants to determine their risk of having an affected child.

AAT concentrations are primarily important when they are lower than normal and/or indicate that the AAT being produced is abnormal. The lower the level of normal AAT, the greater the risk of developing emphysema.

With abnormal AAT, it depends on how much is produced and how abnormal it is. Low concentrations of abnormal AAT in the blood may lead to both emphysema (because of the lack of lung protection) and to liver disease because of the buildup of dysfunctional AAT inside the liver cells producing it.

When DNA testing indicates the presence of one or two abnormal copies of the SERPINA1 gene, less AAT and/or abnormal AAT will be produced and the variant copies can be passed on to the patient’s children. The degree of AAT deficiency and the degree of lung and/or liver damage experienced is very variable. Two people with the same gene copies may have very different disease courses.
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Primary Immune Deficiency

To help decide whether recurrent infections could be due to primary immunodeficiency, your doctor will begin by asking a number of questions, such as what health problems you have, how long infections last, how severe they are and whether they respond to treatment. Your doctor will also want to know whether any close relatives have an inherited immune system disorder. Your doctor will perform a physical examination to look for clues that may indicate the cause of your illness. Primary immune disorders are rare, so your doctor will want to be sure your signs and symptoms aren't caused by a more common health problem.

There are several tests used to diagnose an immune disorder. They include:

  • Blood tests. In most cases, blood tests can reveal abnormalities in the immune system that indicate an immune deficiency disorder. Tests can determine if you have normal levels of infection fighting proteins (immunoglobulin) in your blood. Tests can measure the levels of different blood cells and immune system cells. Abnormal numbers of certain cells can indicate an immune system defect. Other blood tests can determine if your immune system is responding properly and producing antibodies — proteins that identify and kill foreign invaders such as bacteria or viruses.
  • Identifying infections. If you have an infection that's not responding to standard treatment, your doctor may do tests to try to identify exactly what germs are causing it.
  • Prenatal testing. Parents who've already had a child with a primary immunodeficiency disorder may want to have testing done for certain immunodeficiency disorders during future pregnancies. Samples of the amniotic fluid, blood or cells from the tissue that will become the placenta (chorion) are tested for abnormalities. In some cases, DNA testing is done to test for a genetic defect. Test results make it possible to prepare for treatment soon after birth, if necessary.

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The doctor will examine you or your child for sinusitis by:

  • Looking in the nose for signs of polyps
  • Shining a light against the sinus (transillumination) for signs of inflammation
  • Tapping over a sinus area to find infection

Regular x-rays of the sinuses are not very accurate for diagnosing sinusitis.

Viewing the sinuses through a fiberoptic scope (called nasal endoscopy or rhinoscopy) may help diagnose sinusitis. This is usually done by doctors who specialize in ear, nose, and throat problems (ENTs).However, these tests are not very sensitive at detecting sinusitis.

A CT scan of the sinuses may also be used to help diagnose sinusitis or to evaluate the anatomy of the sinuses to determine whether surgery will be beneficial. If sinusitis is thought to involve a tumor or fungal infection, an MRI of the sinuses may be necessary.

If you or your child has chronic or recurrent sinusitis, other tests may include:

  • Allergy testing
  • Blood tests for HIV or other tests for poor immune function
  • Ciliary function tests
  • Nasal cytology
  • Sweat chloride tests for cystic fibrosis.

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Recurring Ear Infections

Pneumatic otoscope

An instrument called a pneumatic otoscope is often the only specialized tool that a doctor needs to make a diagnosis of an ear infection. This instrument enables the doctor to look in the ear and judge how much fluid may be behind the eardrum. With the pneumatic otoscope, the doctor gently puffs air against the eardrum. Normally, this puff of air would cause the eardrum to move. If the middle ear is filled with fluid, your doctor will observe little to no movement of the eardrum.

Additional tests

Your doctor may perform other diagnostic tests if there is any doubt about a diagnosis, if the condition hasn't responded to previous treatments, or if there are other persistent or serious problems.

  • Tympanometry. This test measures the movement of the eardrum. The device, which seals off the ear canal, adjusts air pressure in the canal, thereby causing the eardrum to move. The device quantifies how well the eardrum moves and provides an indirect measure of pressure within the middle ear.
  • Acoustic reflectometry. This test measures how much sound emitted from a device is reflected back from the eardrum — an indirect measure of fluids in the middle ear. Normally, the eardrum absorbs most of the sound. However, the more pressure there is from fluid in the middle ear, the more sound the eardrum will reflect.
  • Tympanocentesis. Rarely, a doctor may use a tiny tube that pierces the eardrum to drain fluid from the middle ear — a procedure called tympanocentesis. Tests to determine the infectious agent in the fluid may be beneficial if an infection hasn't responded well to previous treatments.
Other tests

If your child has had persistent ear infections or persistent fluid buildup in the middle ear, your doctor may refer you to a hearing specialist (audiologist), speech therapist or developmental therapist for tests of hearing, speech skills, language comprehension or developmental abilities.
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Your doctor will ask you to describe how severe your pain is, where it's strongest, how you obtain relief, if other symptoms accompany your headaches and if you've found that some things make your headache worse. A physical examination will reveal the causes of some headaches. If necessary, your doctor will order laboratory tests, x-rays and brain-wave tests. Often these tests are ordered after consultation with a neurologist, a physician who specializes in nerve and brain problems.

Some types of headaches have an allergic basis, but most do not. Before you see an allergist-immunologist for evaluation and treatment of your headaches, you should first visit your primary care physician first to rule out the other more common causes of your headaches.

In some cases, a careful evaluation allergy evaluation may pinpoint the allergen (allergy-causing substance) causing a headache.
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Uncontrolled Itching

Your doctor may diagnose dermatitis after talking to you about your signs and symptoms and examining your skin.

Patch testing

In the case of contact dermatitis, your doctor may conduct patch testing on your skin to see which substances inflame your skin. In this test, your doctor applies small amounts of various substances to your skin under an adhesive covering. During return visits over the next several days, your doctor examines your skin to see if you've had a reaction to any of the substances. This type of testing is most useful for determining if you have specific contact allergies.
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Contact Dermatitis (Poison Ivy/Oak/Sumac)

The diagnosis is mostly based on the skin appearance and a history of exposure to an irritant or an allergen.

Allergy testing with skin patches (called patch testing) may determine which allergen is causing the reaction. Patch testing is used for certain patients who have long-term, repeated contact dermatitis. It requires three office visits and must be done by a health care provider with the experience and skill to interpret the results correctly.

  • On the first visit, small patches of possible allergens are applied to the skin. These patches are removed 48 hours later to see if a reaction has occurred.
  • A third visit about 2 days later is done to look for any delayed reaction.
  • If you have already tested a material on a small area of your skin and noticed a reaction, you should bring the material with you.

Other tests may be used to rule out other possible causes, including skin lesion biopsy or culture of the skin lesion (see skin or mucosal biopsy culture).
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Skin Rashes

There are many useful laboratory and special examinations, which are helpful in the diagnosis of rash:

  • Bacterial culture to check for bacteria on the skin or in a wound
  • Microscopic examination of a scraping of skin with potassium hydroxide to look for fungus
  • Blood tests such as antinuclear antibody (ANA), complete blood count (CBC), liver function tests (LFT), and thyroid function tests
  • Nasal culture using a cotton tip swab to check for Staphylococcus and other bacteria
  • Gram stain (special staining of a sample prior to examination under a microscope) to identify bacteria types
  • Tzanck prep to look for herpes virus under the microscope
  • Skin biopsy(small skin sample or scraping sent for microscopic examination)
  • Patch test to determine contact allergies

Sampling skin material and viewing under direct microscopy is a fast and simple way to help diagnose a rash. When a superficial fungal or yeast infection is suspected, viewing a superficial skin scraping with a potassium hydroxide prep can reveal fungal hyphae or budding cells.

Likewise, suspected bacterial infection can be evaluated by a Gram stain or nasal swab culture. Viral lesionstypically caused by herpes simplex can be viewed under the microscope with a Tzanck smear, which will show giant, multinucleate cells.

Blood tests can be helpful as well (for example, sudden onset of severe psoriasis may be associated with an HIV infection). Anti-streptolysin O (ASO) levels can be helpful in detecting a sudden onset of guttate psoriasis associated with a prior streptococcal throat infection.
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Urticaria (Chronic Hives)


Although it isn't always possible to determine the underlying cause of chronic hives, your doctor will want to learn as much as possible about what might be causing your symptoms. Depending on your symptoms and medical history, your doctor may order one or more tests, including:

  • Blood tests. Your doctor may ask for blood tests to check for levels and function of specific blood cells and proteins.
  • Allergy tests. Your doctor may use skin or blood tests to see whether your hives may be caused by an allergic reaction, especially if the hives seem related to specific triggers.
  • Tests to rule out underlying conditions. You may need additional tests to make certain your hives are not caused by an underlying health condition, such as hepatitis, lupus or thyroid disease.

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If the cause of your hives or angioedema isn't apparent from your medical history or if your symptoms persist or recur often, your doctor may recommend an allergy skin test.

  • Puncture, prick or scratch (percutaneous) test. This is the type of skin test that's usually performed first. Tiny drops of purified allergen extracts are pricked or scratched into your skin's surface. This test is usually performed to identify allergies to pollen, animal dander, foods, insect venom and penicillin.
  • Intradermal (intracutaneous) test. Purified allergen extracts are injected into the skin of your arm. Doctors may perform this test if they strongly suspect you're allergic to an irritant even though your puncture test is negative — especially to an irritant to which a future reaction could be life-threatening, such as insect venom or penicillin.

If your doctor suspects hereditary angioedema, he or she may order blood tests to check for levels and function of specific blood proteins.
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Insect Allergies (Bee Sting)

If you've had a reaction to bee stings that suggests you might be allergic to bee venom, your doctor may suggest one or both of the following tests:

  • Skin test. During skin testing, a small amount of purified allergen extract (in this case, bee venom) is injected into the skin of your arm or upper back. This test is safe and won't cause any serious reactions. If you're allergic to bee stings, you develop a raised bump (hive) at the test location on your skin. Allergy specialists usually are best equipped to perform allergy skin tests.
  • Allergy blood test. A blood test (sometimes called the radioallergosorbent test, or RAST) can measure your immune system's response to bee venom by measuring the amount of allergy-causing antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. A blood sample is sent to a medical laboratory, where it can be tested for evidence of sensitivity to possible allergens.

Allergy skin tests are the most accurate tests for insect allergies. But if the allergy skin test is negative — and your doctor still thinks you might have a stinging insect allergy — you may need an allergy blood test to double-check. Your doctor may also want to test you for allergies to yellow jackets, hornets and wasps — which can cause allergic reactions similar to those of bee stings.
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