Allergy testing for Teicoplanin is much more unreliable than for other similar drugs. This means that we run the risk of missing serious Teicoplanin allergy, and these patients will be given another dose in future, not knowing that they are seriously allergic. Serious allergic reactions, also known as anaphylaxis, can be life threatening. The patients which we recruit to our study will come to us through the perioperative allergy service. They will have had a reaction to a general anaesthetic, but will also have had teicoplanin as part of the anaesthetic. We are not sure why allergy skin testing, which is fairly reliable for most other drugs, is so unreliable in detecting teicoplanin allergy. We do know that some drugs need to mix with proteins in the blood before they trigger an allergy. We would like to replicate this by mixing the teicoplanin with the patients' own blood and using this for the skin testing, to see if we get a more reliable result compared with the plain drug. Using the patient's own serum to do skin testing is an established test (the 'autologous serum test') used in certain immunological conditions, we are simply going to use it as a vehicle to test our theory. We will recruit 20 adult patients referred with a recent history of anaphylaxis under anaesthesia, where teicoplanin has been given and is one of the drugs under suspicion of having caused the allergy. In addition to the usual allergy skin testing, which would be done anyway as part of standard allergy investigation, we will perform extra tests using autologous serum for this trial. We hope to find a better way of testing for Teicoplanin allergy, so that patients are not put at risk where the allergy has been missed because of an unreliable test.