A false positive or false negative result of an allergy test in common in both the blood test and the skin prick test. No allergy test is "foolproof, there's always a change of false positive or negative" (C.W. Williams). Although it is much more common to get a false positive result then a false negative the false negative is still possible. "50-60 percent of all skin prick tests yield “false positive” results" (FARE).
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False Positive
A false positive is when your test looks like you are positive but you are actually negative (Gupta). For a skin prick test this would look like you have reacted to the allergen and have the raised red bump but you do not have this allergy. Unfortunately there is no way to know in the moment that you are having a false positive reaction. For a blood test a false positive would be the computer recording a larger amount of IgE antibodies then are needed in your body for that specific allergen. Your body could also be producing more IgE antibodies for that allergen then you need. False Negative A false negative is when your test looks like you are negative when you are actually positive (Gupta). For a skin prick test this would look like there was no reaction at all to the skin from the allergen when you should be reacting to this. A factor that could be making you have a false negative is having antihistamine in your body. An antihistamine blocks histamine that is needed to show a reaction (Gupta). Having an antihistamine present in your body can make you have a false negative to the test. For a blood test a false negative would be the body not producing enough IgE antibodies for that allergen or the computer not counting the correct amount of IgE antibodies. |