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There is a related group of drugs known as cephalosporins that exhibit a 6% cross sensitivity reaction to penicillin allergy sufferers.

What's the meaning of cross in this sentence?
Is sensitivity reaction used to mean allergy?

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up vote 5 down vote accepted

Cross sensitivity is a medical term that means that if you have an allergy to some substance then you are much likely to have an allergy to similar substances. For example if you are allergic to penicillin you also may be allergic to cephalosporins.

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I'm not medically qualified, but I do have a potentially life-threatening allergy to penicillin. Even though I've no idea what cephalosporins are, I would avoid them on the grounds that the probable meaning of "cross-sensitivity" is that there's a 6% chance I'd have a fatal reaction to them as well. So "cross" here means "applicable across both contexts" (i.e. - the sensitivity applies to both cephalosporins and penicillin, for 6% of subjects tested).

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1) Yes, the sensitivity here refers to an immunological/allergic reaction.
2) "cross" in this case is roughly synonymous to "across the range of" [similar substances], though in this case, it is limited to a range of two. It is a subset of a wider range, so the mechanism of cross-sensitivity is the same.

Here's The Oxford Dictionary of Biochemistry and Molecular Biology :

cross‐sensitivity a state of immunological hypersensitivity to one substance produced by priming an animal with another substance that bears cross‐reacting antigen.

The Oxford Dictionary of Biochemistry and Molecular Biology. Ed Richard Cammack, Teresa Atwood, Peter Campbell, Howard Parish, Anthony Smith, Frank Vella, and John Stirling. Oxford University Press, 2008.

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