Background In our clinic we routinely patch test patients referred from occupational health for the investigation of latex contact urticaria. We also undertake both patch and prick testing (where indicated) in patients referred with persistent dermatitis/eczema. If investigation of allergic skin disease is undertaken by a non-dermatologist, it is unlikely that patch testing will be performed.
Objective To carry out a retrospective analysis of patients who had been prick tested to establish whether an incomplete diagnosis would have been reached if patch testing had been omitted.
Methods Details of patients who had attended for patch testing between July 2004 and December 2005 were analysed. Patients who had had prick tests and patch testing were identified. The outcomes of prick tests and patch testing were documented together with the clinical relevance.
Results Three hundred and thirty out of 1060 patients referred to the clinic were prick tested. 54.2% patients were referred from dermatologists. 26.6% were referred from occupational health, 68 patients had positive reactions on prick testing of whom 36 had positive patch tests (52.9%), which were of current relevance in 27 patients (39.7%). Nine out of 106 health workers referred to exclude latex contact urticaria had positive prick tests to latex. Fifty of these patients demonstrated delayed-type hypersensitivity with nickel, cobalt, rubber and its additives being the most common allergens found. Of the 262 patients who had negative prick tests, 121 had positive patch tests (46.1%) of current relevance to patient history in 92 subjects (35.1%). While none of the six patients referred for investigation of reaction to local anaesthetics had a positive prick test, one was allergic to local anaesthetic on patch testing.
Conclusion Omission of patch testing from the investigation of allergic skin disease, even when contact urticaria may be the sole suspected diagnosis, would result in the frequent missed diagnosis of contact allergy. We recommend that patients with suspected allergic skin disease are investigated in an environment where investigation of both immediate- and delayed-type hypersensitivity can be undertaken. In particular, patients with atopic eczema, suspected latex rubber allergy, hand dermatitis (particularly occupational) and drug reactions should be targeted to receive both investigations.