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Internist
Internist, Board Certified Physician
Category: Medical
Satisfied Customers: 1066
Experience:  MBBS,MD (USA)Diplomate American Board of Internal Medicine
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My whole family is allergic to cats . My son has shown all

Resolved Question:

Hi my whole family is allergic to cats . My son has shown all the signs and symptoms to being allergic and only has these when in contact with a cat( which I do not allow , it is out of my hands) . But I got a rast allergy test done and it came back negative, I don't know how this is possible as I've dealt with this for 3 years with him and I'm 100% . Can these tests be wrong ??
Kind regards
Submitted: 1 year ago.
Category: Medical
Expert:  Internist replied 1 year ago.
Hi there,I am online and will be happy to answer your questions.I am sorry to hear about your problem.Thank you for your patience. thank you for asking this question.sensitivity of this test ( that is the ability to detect allergy ) is not very good. however specificity ( that is if test comes out as positive, it is highly suggestive of allergic to that subsatance ) is fairly high. so , yes it can be negative in patients who are actually allergic
Expert:  Internist replied 1 year ago.
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Customer: replied 1 year ago.
Hi thankyou for your quick response , can you explain briefly in laymans terms but why it could come back as negative if if he is allergic??
Expert:  Internist replied 1 year ago.

thank you for replying.

the sensitivity and specificity of test i was refering to is as follows.

the sensitivity of RAST is not as high. meaning it can miss some cases of pateints with allergy. ( meaning a negative test does not always rule out the disease )

specificity is quite high, meaning if test comes out to be positive, it is more likely to be true positive ( meaning patient is allergic, meaning a positive test rules in the disease most of the times )

 

to answer why, this is just the inherent property of a test used to diagnose a condition. no test ( almost none ) has 100 % sensitivity or 100 % specificity. ( because some other unknonwn particles in blood can react with the reagants and give false positive or false negative test results )

 

I am sorry if i confused you. please let me know if i should explain more

thanks