The foundation of medicine is the General Practitionner. In my point of view, it is very important, in the increasing prevalence of allergic manifestations that GP be involved in the diagnosis of these problems.
He must ask why do the research of allergy and how, and what test to use ? and assess the severity of the disorder (severe: angioedema, asthma ?) worsening over time, their frequency, periannial or seasonal, professional or domestic nature...Because management includes an etiologic diagnosis. Back to family and personal history, environmental and occupational context, he can identify the allergen(s) in cause.
First Generalists test (total IgE) or Phadiatop (or other, there are many and excellent) will confirm atopy. Specific IgE can be used to identify the allergen(s)in cause. To confirm an evident diagnosis the GP can use this second test; If not, in case of severe disorders, to decide and conduct desensitivation the opinion of the Allergist is necessary. Check that there are no interfering drug taken with the result (medications against histamine,etc.).
The specialist can help the GP to precise the etiologic diagnosis and to manage the treatment, but the result of the investigations and the follow up are explained and made by the GP and the Allergist.
A specific IgE alone does not make an allergy diagnosis, unless it is backed up by family history and clinical symptoms, as well as allergy reaction provoked in real life by the respective allergen.But even if all that fits, a specific IgE may still not be the proof of a specific allergy since a patient may have specific IgE antibodies that do no harm( for example anti cow's milk IgE in adults) and on the other hand , one can be very allergic but have no specific IgE to any allergen ( his antibodies might sit on IgG sub classes).
Hence the final conclusion of allergy , yes or no, should be driven by an allergy specialist.
I agree with Carmi; it's clear that the allergy dagnosis can only be based on prescription blood test but on a comparison from the interview data (environment:home,business,food,etc.)and skin tests...however GP can identify the responsability of many allergens and partipate in the front-line diagnostics provided he had a basic training of good quality. I think that many patients with diagnostic of allergy could be largely driven by a well-trained GP...remains that skin tests are an essentiel step .
GP can deal basically with allergic pt (BA, Allergic Rhinitis, United airway syndrome or Skin allergy. History & examination lead to type of allergy. Skin prick test (SPT) is essential to determine type of causative allergen(s) for prevention. RAST can be done if there is contraindication of SPT. After that, GP can guide pt to consultant (Pneumologist, Otorhinolaryngologist or dermatologist) according to type of allergy. But if GP is graded with family doctor certificate (Master, MD or board), he can start to manage any of these types of allergy & in case of failure of treatment or presence of complication, it is better to guide pt to consultant (Pneumologist, Otorhinolaryngologist or dermatologist) according to type of allergy.