Diagnostic Tests

Your allergist has several diagnostic tools to his disposal to help determine whether you have asthma or other allergic diseases. Your allergy doctor can make an assessment, based on your history and physical findings, on the appropriate tests that he can perform in his office or whether to send you to another facility for additional diagnostic testing.

Types of Allergy testing

Allergy Skin Testing

Allergy skin testing is the gold-standard method to determine our allergies. The test is performed by pricking the patient’s skin with a small drop of allergen, to safely introduce the allergen to your body. If you are allergic to the specific allergen you will see a “wheal and flare” reaction that appears as a welt that looks like a mosquito bite.   The allergy prick skin test is used by allergists to determine if you are allergic to various allergens such as environmental aeroallergens (pollen, dust mites, mold spores, pets), foods, insects (bees, hornets, wasps), or drugs (penicillin).

Determining what we are allergic to is very important since it can help decide what proactive measures to take to avoid the allergens, and/or for a trusted allergy doctor to determine what treatment plan can be prescribed for relief.

Allergy Blood Testing

Blood allergy testing is an alternative to allergy skin testing. It is also called RAST testing.  It is often used if a patient cannot have allergy skin testing due to various conditions.  An example would be in certain individuals who have “dermographism” or severely sensitive skin.  These individuals develop welts anytime the skin is rubbed, stroked or poked, thus making it difficult to distinguish whether the reaction is due to an allergic reaction or mere sensitive skin.  Another situation where RAST allergy skin testing is warranted is when allergy testing is needed in someone who cannot discontinue medications that may interfere with skin test.

The results obtained from RAST allergy testing are helpful, just like allergy skin testing in determining what actions to take to prevent or treat allergy problems

Food and Drug Oral Challenge

Food Oral Challenge – There are times when food allergy testing does not correspond to the patient’s symptoms. An example would be when one has a positive allergy test to milk or wheat but still it is still unclear if the food is actually making the patient sick. In this case it is best to do a blinded oral challenge wherein a patient is given food, in a supervised setting, and observed for clinical symptoms. If the results are “negative”, it is safe for the patient to eat that food; a “positive” reaction indicates that the food must be avoided due to allergies.

Drug Challenge – The only valid, FDA-approved, commercially available test for drug allergy is to penicillin. All other allergy tests to medications are not validated and have yet unproven predictive value

When confronted with a problem with drug allergies other than penicillin, the physician must rely heavily on a range of information including the history given the patient. If it seems highly likely that there is a drug allergy, other methods may be implemented to determine drug hypersensitivity.

There are published protocols in the literature to skin test for non-penicillin drugs, however due to their unproven predictive values, it is necessary to also do a drug challenge to determine clinical relevance.   This is performed by giving incremental doses of the implicated medication over regular intervals until the therapeutic dose is reached. If the drug challenge is negative then the patient can continue to take the drug. However if symptoms develop, they need to avoid the drug and consider alternative choices.



Types of Asthma Tests

Pulmonary Function Testing

The Pulmonary Function Test(PFT) or spirometry is a simple “blowing test” that helps assesses our lung function.  The test is performed by blowing into a computer which then calculates the lung function. The PFT readings reveal if a patient has an obstruction or restriction of their lungs. Obstruction is more indicative of asthma or Chronic Obstructive Pulmonary Disease (COPD), while restriction could indicate conditions that limit the lungs’ ability to expand or contract adequately. A few examples of conditions that can cause a restrictive pattern would be being overweight, spinal problems, and congestive heart failure

Peak Flow Readings

Anyone with asthma should have a peak flow meter. It is a portable method of gauging your lung function. It is used by a patient at home to determine asthma is causing lung impairment.

A peak flow meter could be crucial because people are often unable to accurately judge their own asthma. Allergists can train us on how to use it to determine how our asthma is doing, and when/ whether or not we should use our rescue inhaler or even go to the emergency room.

Methacholine Challenge

A normal PFT does not necessarily mean you do not have asthma.  Thus, a methacholine challenge test is used when your doctor suspects asthma even though a PFT is normal. Methacholine is a chemical that can induce bronchospasm in patients who have asthma or hyperactive airway disease.   In this test, the patient inhales incremental doses of methacholine and if the patient has asthma, bronchospasm will occur and the PFT will become abnormal revealing an obstructive pattern as seen in asthma.  If positive, appropriate asthma treatment can be recommended by your asthma doctor.

Exhaled Nitric oxide

This test is mostly used in research settings but is slowly being accepted and practiced in the medical community. Patients with allergic inflammation in their lungs, as seen in asthma, often have an elevated amount of nitric oxide (eNO) in their exhaled breath. It is useful in some asthma patients who have normal pulmonary function tests since the presence of an elevated amount of eNO could still indicate allergic asthma, despite a normal PFT.

The test is also useful in monitoring asthma treatment. Exhaled nitric oxide has been shown to decrease significantly in asthma patients who receive controller asthma medications such as inhaled corticosteroids.