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Diagnostic tests

Dermatology tests include:

  • Dermatoscopy for pigmented lesions, such as moles
  • KOH examination for superficial fungal infections
  • Microscopic examination for parasites (Scabies prep)
  • Patch testing for contact allergy
  • Skin biopsies for histopathologic evaluation, immunofluorescence, and microbiologic culture
  • Tzanck smear for Herpes zoster
  • Gram’s Staining for bacterial infections

Diagnostic tests are indicated when the cause of a skin lesion or disease is not obvious from history and physical examination alone.


One procedure is a punch biopsy, in which a tubular punch (diameter usually 4 mm) is inserted into deep dermal or subcutaneous tissue to obtain a specimen, which is snipped off at its base. More superficial lesions may be biopsied by shaving with a scalpel or razor blade. Bleeding is controlled by aluminum chloride solution or electrodesiccation; large incisions are closed by sutures. Larger or deeper biopsies can be done by excising a wedge of skin with a scalpel. Pigmented lesions are often excised for histologic evaluation of depth; if too superficial, definitive diagnosis may be impossible. Diagnosis and cure can often be achieved simultaneously for most small tumors by complete excision that includes a small border of normal skin.

We at COSMETIQUE prepare slides, do microscopy and take images, which are then sent to our collaboration lab in USA, Rao Dermatology Lab, for evaluation and final diagnosis.


Skin scrapings help diagnose fungal infections and scabies. For fungal infection, scale is taken from the border of the lesion and placed onto a microscope slide. Then a drop of 10 to 20% potassium hydroxide is added, followed by Swartz Lamkin staining. Hyphae, budding yeast, or both confirm the diagnosis of tinea or candidiasis. For scabies, scrapings are taken from suspected burrows and placed directly under a coverslip with mineral oil; findings of mites, feces, or eggs confirm the diagnosis.

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Diagnosis for fungal infection

Tzanck testing

Tzanck testing is used to diagnose viral disease, such as herpes simplex and herpes zoster, and can be done when active intact vesicles are present. Tzanck testing cannot distinguish between herpes simplex and herpes zoster infections. An intact blister is the preferred lesion for examination. The blister/vesicle is un-roofed with a sharp blade, and the base of the un-roofed vesicle is scraped with a #15 scalpel blade. The scrapings are transferred to a slide and stained with Wright stain or Giemsa stain. Multinucleated giant cells are a sign of herpes infection.

Patch Test

Patch testing is a specialized procedure carried out to find out whether your skin condition is caused by an allergy to substances (these substances are called allergens) which come into contact with your skin, such as products at home, at work or in leisure activities. You can then be advised of the names of any identified allergens in order to help you to avoid them.

Patch testing is generally done to see whether a particular substance is causing allergic skin irritation (contact dermatitis). Patch tests can detect delayed allergic reactions, which can take several days to develop.

Patch tests don’t use needles. Instead, allergens are applied to patches, which are then placed on your skin. During a patch test, your skin may be exposed to 20 to 30 extracts of substances that can cause contact dermatitis. These can include latex, medications, fragrances, preservatives, hair dyes, metals and resins.

You wear the patches on your arm or back for 48 hours. During this time, you should avoid bathing and activities that cause heavy sweating. The patches are removed when you return to your doctor’s office. Irritated skin at the patch site may indicate an allergy.

Gram Staining

Gram staining is a method of differentiating bacterial species into two large groups i.e. gram-positive and gram-negative.

Gram staining differentiates bacteria by the chemical and physical properties of their cell walls by detecting peptidoglycan, which is present in a thick layer in gram-positive bacteria. In a Gram stain test, gram-positive bacteria retain the crystal violet dye, while a counter stain (commonly safranin or fuchsine) added after the crystal violet gives all Gram-negative bacteria a pink color. The Gram stain is almost always the first step in the identification of a bacterial organism. Gram staining is a valuable diagnostic tool in clinical setting, as it helps the physician to chose a more effective narrow spectrum antibiotic.

Fungal culture

Dermatophytosis (tinea or ringworm) of the scalp, glabrous skin, and nails is caused by a closely related group of fungi known as dermatophytes which have the ability to utilise keratin as a nutrient source, i.e. they have a unique enzymatic capacity (keratinase).

This test can help determine if you have a fungal infection and, if needed, what type of fungus is causing the infection. This information can help your doctor determine the most effective treatment course.

Dermatophyte infections are very common in our country where hot and humid climate in association with poor hygienic conditions play an important role in the growth of these fungi.

Dermatophyte Test Medium is used for the selective isolation of dermatophytic fungi.