All pruritic dogs (chronic scratching) will usually have these kinds of cheap and extensive tests performed on their first vet visit. NOTE if an obvious sign of a dog allergy is not available then these skin tests are always performed before diet and food allergy tests.
DOG SKIN SCRAPINGS to diagnose skin allergy causes
These are classed as anything that is external or above the skin and are usually aimed at identifying parasites (including fleas) that are causing a dogs allergies.
- Skin scrapes using mineral oil to find parasites (this includes juvenile and adults mites or eggs).
- Dog Coat brushings to find parasites, eggs or flea dirt.
- Hair plucks are used to identify parasites (eggs and dermatophytes).
- Wet paper test for fleas (similar to the mineral oil scrape). The process involves dragging a white paper under the tap and then hold it under your dog while you shake its hair. This test will get loose dirt and hair as well as the flea faeces or blood components which appear as either black or red (blood engorged) dots.
- Acetate tape strips: unstained to look for parasites or eggs or stained for cytological (study of cells in terms of structure, function and chemistry ) examination.
- Cytology of:
- impression smears or tape strips or aural (ear) discharge for bacteria or yeast,
- neutrophils (examination of white blood cells)
- acanthocytes (form of abnormal red blood cell that has a spiked cell membrane)
- neoplastic cells (uncontrolled growth of abnormal tissue called a tumor).
- The dogs response (stopping scratching) whether or not fleas have been identified in their many stages, will give a good indication of whether the dog allergy was caused by a flea.
- Sarcoptic mange antibody titre. Sarcoptic mange is caused by the itch mite and tends to affect mostly the abdomen and hindquarters of the dog. Sarcoptid mites are difficult to find on skin scrapes and that is why blood test are used (but the infection must be at least 4 weeks old to show a positive result).
Sarcoptic mange should always be ruled out prior to further investigations, such as intradermal (within or between the layers of the skin ) allergy testing, as mites may cross-react with some common house dust mite giving a false positive reactions.
SKIN BIOSPSY for dog allergy testing
Obviously visual inspection and skin tapes etc are very unobtrusive, but they only get the external stuff that will easily fall off and of course not all parasites sit in the outside of your dog.
Because of expense and trauma considerations to a dog Skin biopsy should only be performed if the disease appears unusual and cant be indentured by the previous tests (nor is a candidate for a food allergy reaction).
Superficial perivascular dermatitis (a classification of inflammatory dermatosis in which the reaction is centred around superficial or deep dermal blood vessels) is a common response to many diseases, such as: infection, parasites or allergy,
A dog skin allergy Biopsy is called for if you observe nodular disease, severe clinical signs, if there is no response to rational therapy or if you suspect there may be a disease that requires treatment with medications with severe side effects.
Nodular disease is where nodules in the wall of the large intestine, cecum, and occasionally, the ileum. The nodules are filled with caseous material (a form of necrosis DEAD SKIN in which tissue is changed into a dry, amorphous mass resembling cheese) and result from host response to encystment of the larvae of Oesophagostomum species (a worm)
Generally it is recommended to take multiple samples from different areas and to use a dog dermatopathologist instead of a general pathologist.
DOG FOOD ALLERGY TESTING
ONLY AFTER all parasitic diseases and infections have been ruled out should dog food allergy testing (ie exclusion diets) be used.
as extensively previously discussed on this site: the chosen exclusion diet should be fed as the sole source of food for at least six weeks (preferably eight to 10 weeks, but this is often not possible).