Seasonal allergies cause symptoms such as runny nose, sneezing, nasal congestion and itchy, watery eyes. These symptoms are typically caused by outdoor allergens that bloom during certain seasons. There are two main types of diagnostic testing that can be used to determine the specific allergen that is the cause of the symptoms--skin tests and blood tests. Once the specific allergen is known, treatment can be initiated.
Significance
The symptoms associated with allergic rhinitis can be burdensome and uncomfortable. In addition to nasal congestion, sneezing and itchy eyes, some patients experience night time cough, fatigue and difficulty with smell and taste. Diagnosing the specific allergen is important because this allows the patient to avoid the allergen and to obtain treatment. According to the University of Maryland Medical Center, the most common causes of seasonal allergic rhinitis are ragweed, grass pollen, tree pollen and fungus.
Skin Testing
Skin testing can be used in patients of all ages to diagnose seasonal allergies. This test involves pricking the skin with a small amount of allergen extract. Histamine, which should react on all patient's skin, and saline, which should not react on any patient's skin, is also applied. Twenty minutes after the skin pricks are placed, the allergist measures the reaction and determines which substances the patient's body reacts to. In conjunction with the history regarding the time in which the patient has symptoms, this allows the physician to determine which allergens are causing symptoms.
Blood Tests
Blood testing is typically performed in patients who cannot undergo skin testing. In this test, blood is drawn to measure the allergen-specific immunoglobulin E, or IgE. IgE is an antibody that forms when the body responds to harmless substances as though they were harmful and is the antibody that mediates the allergic response. Allergen-specific IgE levels above a certain threshold indicate that the body is able to mount a response to that allergen, says the Mayo Clinic.
Considerations
Skin testing is the preferred diagnostic test because it has the lowest false negative rate. In certain situations, however, it can't be performed. Medications such as antihistamines and antidepressants can interfere with the ability of the body to mount a response to the skin testing. Skin testing is performed with caution in patients with asthma. If the patient is already having problems with asthma, skin testing can worsen the symptoms. Finally, skin testing is difficult to perform in patients with a severe rash such as atopic dermatitis.
Risks
The main risk associated with skin prick testing is that the reactions to the allergens produce a hive-like reaction which can be uncomfortable. This reaction improves over time and a cream can be placed over the skin test results to soothe the skin. There is a slight risk of developing a severe, systemic reaction during skin testing and for this reason the testing is performed in an allergist's office. The main risk associated with blood testing is the discomfort of a blood draw. Fortunately, most patients have very few side effects from either type of testing.
