Diagnostic Tests for Rash

Diagnostic Test list for Rash:

The list of diagnostic tests mentioned in various sources as used in the diagnosis of Rash includes:

Skin examination
Physical examination
- Note characteristics of skin rash - e.g. macular, papular, pustular, vesicular, bullous, scaly, ulcers - will help determine the cause of the rash (e.g. a macular or papular rash may suggest eczema, contact dermatitis, exfoliative dermatitis, pityriasis rosea or a drug reaction; a pustular rash may suggest staphylococcus, scabies or a fungal skin infection; a vesicular or bullous rash may suggest chicken pox, dermatitis herpetiformis, contact dermatitis, pemphigus, bullous impetigo or nummular eczema; a scaly rash may suggest ichthyosis, psoriasis, lichen planus, fungal skin infection, exfoliative dermatitis or a drug eruption; an ulcerative rash may suggest a basal cell carcinoma).
- Note distribution of the skin affected - e.g. focal or diffuse (e.g. focal rash may suggest fungal skin infection, scabies, contact dermatitis, skin tumor, nummular eczema or impetigo; diffuse rash may suggest psoriasis, lichen planus, eczema, drug eruptions, dermatitis herpetiformis, pemphigus, pityriasis rosea or tinea versicolor.
- What areas of the body does it primarily involve - e.g. extremities, face, trunk? - will help determine the cause (e.g. extremities may suggest atopic dermatitis, tinea, psoriasis or insect bites; typical lower leg rashes include keratitis pilaris, erythema nodosum, nummular dermatitis, stress dermatitis, necrobiosis lipoidica; typical rashes on the front of the knees include psoriasis and dermatitis herpetiformis).
- Look for any features that may suggest meningococcal disease. One of the main tests of the meningococcal rash is that it does not fade under pressure. In other words, the skin does not turn whiter or go paler under pressure. Unfortunately, this is not always true in the early stages of the rash, so the rash needs to be assessed regularly to avoid a misdiagnosis in the early stages. The pressure test involves pressing on the rash to see whether it fades. One convenient way is to press on the rash with a clear see-throughdrinking glass, to see through the glass how the rash responds
Blood tests
- Full blood count
- Blood cultures, if unwell and fever
- Radioallergosorbent testing (RAST) - to test for specific allergens that may be triggering eczema ( 90% relevant if negative, but only 20% relevant if positive).
- Ig E levels are increased with atopic dermatitis
- Viral serology tests, if indicated
Skin tests
- Microscopic examination of scrapings of any skin burrows (to detect scabies mite) or skin rash (to rule out fungal infection)
- Patch testing to detect skin allergies
- Skin biopsy may be necessary
Swab of any discharge - for bacteria or fungi.
Viral culture, if suspect viral infection such as herpes simplex, herpes zoster (shingles), varicella zoster (chicken pox)

Conditions listing medical symptoms: Rash:

The following list of conditions have 'Rash' or similar listed as a symptom in our database. This computer-generated list may be inaccurate or incomplete. Always seek prompt professional medical advice about the cause of any symptom.

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