Many people wonder if they should stop taking allergy medication before a blood test. This is a common question, as various medications can influence laboratory results. The impact of allergy medicines on blood work depends on the specific type of medication and the purpose of the blood test. Understanding these nuances helps ensure accurate diagnostic results.
How Allergy Medications Can Influence Test Results
Allergy medications primarily modulate the body’s immune response. Antihistamines, for instance, block histamine, a chemical released during an allergic reaction, alleviating symptoms like itching, sneezing, and congestion. While beneficial for symptom relief, this mechanism can interfere with diagnostic tests that rely on observing the body’s natural allergic response.
Some ingredients in cold and allergy medications can have broader systemic effects. They might influence liver function, altering liver enzyme tests. These medications could also affect complete blood counts, subtly changing white or red blood cell levels, or impact inflammatory markers. Considering medication use is important when interpreting blood test results.
Specific Blood Tests and Potential Interactions
The effect of allergy medications varies significantly depending on the type of blood test.
IgE Antibody Tests
For allergy-specific blood tests, such as those measuring Immunoglobulin E (IgE) antibodies, common over-the-counter antihistamines typically do not affect the results. These tests measure existing antibodies in the blood, and antihistamines do not alter their levels. Therefore, you generally do not need to stop antihistamine medication for an IgE blood test.
Allergy Skin Prick Tests
Antihistamines significantly interfere with allergy skin prick tests. These tests rely on the body’s histamine response to identify allergens. Blocking this response with antihistamines can lead to false-negative results, meaning an allergy might be present but not detected. Healthcare providers typically advise stopping oral antihistamines for three to seven days before a skin prick test.
Decongestants
Decongestants, found in many cold and allergy formulations, work by narrowing blood vessels to reduce swelling. This action can lead to a temporary increase in blood pressure and, in some cases, blood sugar levels. While this effect might be relevant for individuals with pre-existing conditions like hypertension or diabetes, it usually does not pose a significant issue for routine blood work such as a complete blood count (CBC) or basic metabolic panel (BMP).
Nasal Steroid Sprays vs. Oral Steroids
Nasal steroid sprays (intranasal corticosteroids) have minimal systemic absorption when used at recommended doses. Studies indicate they generally do not significantly affect blood markers such as white blood cell counts, or levels of blood sugar and HbA1c, even in diabetic patients. Consequently, these medications typically do not need to be discontinued before most blood tests or allergy skin tests.
In contrast, oral steroids, like prednisone, are absorbed throughout the body and can have a more pronounced impact. They can elevate blood sugar, alter complete blood counts by affecting white and red blood cell numbers, and influence inflammatory markers. The effects of oral steroids on blood work can persist for many hours after a dose.
Essential Steps Before Your Blood Draw
Before any blood draw, communicate openly with your healthcare provider or the lab technician. Inform them about all medications you are currently taking, including any over-the-counter allergy medicines, supplements, or herbal remedies. This comprehensive disclosure allows medical professionals to accurately interpret your test results and understand any potential influences.
Do not discontinue any prescribed medications, including allergy medicines, without explicit instruction from your doctor. Stopping certain medications abruptly can sometimes lead to adverse health effects. If your doctor advises you to stop a medication for a specific test, they will provide clear guidance on how long before the test this should occur.
For instance, if you are scheduled for an allergy skin test, your doctor will likely provide specific timing for stopping antihistamines, which could be several days in advance. However, for most routine blood tests, such as complete blood counts or basic metabolic panels, common allergy medications typically do not require cessation. Being transparent about your medication use ensures that your healthcare team can provide the most accurate diagnosis and treatment plan.