KOH test
Encyclopedia
The KOH Test for Candida albicans, also known as a potassium hydroxide
preparation, is a quick, inexpensive fungal test to differentiate between dermatophyte
s and Candida albicans
symptoms from other skin disorders like psoriasis
and eczema
.
Dermatophytes are a type of fungus
that invades the top layer of the skin, hair, or nails. There are three genera of fungi commonly implicated: Trichophyton
(found in skin, nail, and hair infections), Epidermophyton
(skin and nail infections), and Microsporum
(skin and hair infections).
Dermatophytes produce an infection commonly known as ringworm or tinea. It can appear as “jock itch
” in the groin or inner thighs (tinea
cruris); on the scalp and hair (tinea capitis
) resulting in brittle hair shafts that fall out easily. Tinea unguium affects the nails and athlete's foot
(tinea pedis) affects the feet. Tinea versicolor
refers to a fungal infection of the skin caused by Malassezia furfur
. It appears anywhere on the skin and produces red or gray, scaly patches of itchy skin. Deeper infections may be discoloured, ulcerative and purulent.
A Candida yeast infection can also be identified by a KOH test by taking scrapings from the mouth (oral thrush), vagina (vaginitis
) and skin (candidiasis
). There are over 40 different fungus species known to cause disease in humans, of which Candida albicans is the most common and most frequently tested for.
Results are usually available while the patient waits or the next day if sent to a clinical laboratory.
The KOH test procedure may be performed by a physician
, assistant or a nurse. If fungal cultures are required, the test is performed by a technologist who specializes in microbiology.
Skin, nail, or hair samples are collected from the infected area on the patient. For skin samples, a scalpel or edge of a glass slide is used to gently scrape skin scales from the infected area. For hair samples, a forceps is used to remove hair shafts and follicles from the infected site. If the test is being sent to a laboratory, the scrapings are placed in a sterile covered container. For immediate tests, the scrapings are placed directly onto a microscope slide and are covered with 10% or 20% potassium hydroxide.
The slide is left to stand until clear, normally between five and fifteen minutes, in order to dissolve skin cells, hair, and debris. To enhance clearing dimethyl sulfoxide
can be added to the slide. To make the fungi easier to see lactophenol cotton blue stain
can be added. The slide is gently heated to speed up the action of the KOH. Adding calcofluor white stain to the slide will cause the fungi to become fluorescent, making them easier to identify under a fluorescent microscope
.
s formed directly from the hyphae (arthroconidia). Under the microscope Tinea versicolor is recognized by curved hyphae and round yeast forms that give it a spaghetti-and-meatball appearance.
Yeast cells appear round or oval and budding forms may be seen. The KOH prep cannot identify the specific organism; the specimen can be submitted for fungal culture to identify the organism.
A normal, or negative, KOH test shows no fungi (no dermatophytes or yeast). Dermatophytes or yeast seen on a KOH test indicate the person has a fungal infection. Follow-up tests are usually unnecessary.
The skin may be sore after the test because of the tissue being scraped off the top of the surface of the skin.
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
preparation, is a quick, inexpensive fungal test to differentiate between dermatophyte
Dermatophyte
Dermatophytes are a common label for a group of three types of fungus that commonly causes skin disease in animals and humans. These anamorphic genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera...
s and Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...
symptoms from other skin disorders like psoriasis
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...
and eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
.
Dermatophytes are a type of fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
that invades the top layer of the skin, hair, or nails. There are three genera of fungi commonly implicated: Trichophyton
Trichophyton
The fungus genus Trichophyton is characterized by the development of both smooth-walled macro- and microconidia. Macroconidia are mostly borne laterally directly on the hyphae or on short pedicels, and are thin- or thick-walled, clavate to fusiform, and range from 4 to 8 by 8 to 50 um in size....
(found in skin, nail, and hair infections), Epidermophyton
Epidermophyton
Epidermophyton is a genus of fungus causing superficial and cutaneous mycoses, including E. floccosum, a cause of tinea corporis , tinea cruris , tinea pedis , and onychomycosis or tinea unguium, a fungal infection of the nail bed.-External links:**...
(skin and nail infections), and Microsporum
Microsporum
Microsporum is a genus of fungi that causes tinea capitis, tinea corpus, ringworm, and other dermatophytoses. Microsporum forms both macroconidia and microconidia on short conidiophores...
(skin and hair infections).
Dermatophytes produce an infection commonly known as ringworm or tinea. It can appear as “jock itch
Jock itch
Tinea cruris, also known as crotch itch, crotch rot, Dhobie itch, eczema marginatum, gym itch, jock itch, and ringworm of the groin in American English is a dermatophyte fungal infection of the groin region in either sex, though more often seen in males...
” in the groin or inner thighs (tinea
Tinea
Tinea is a general term used to describe skin mycoses. The term ringworm is even less precise, but is usually considered a synonym.It is sometimes equated with dermatophytosis, and it is true that most conditions identified as "tinea" are members of the imperfect fungi that make up the dermatophytes...
cruris); on the scalp and hair (tinea capitis
Tinea capitis
Tinea capitis is a superficial fungal infection of the scalp. The disease is primarily caused by dermatophytes in the Trichophyton and Microsporum genera that invade the hair shaft...
) resulting in brittle hair shafts that fall out easily. Tinea unguium affects the nails and athlete's foot
Athlete's foot
Athlete's foot is a fungal infection of the skin that causes scaling, flaking, and itch of affected areas. It is caused by fungi in the genus Trichophyton and is typically transmitted in moist areas where people walk barefoot, such as showers or bathhouses...
(tinea pedis) affects the feet. Tinea versicolor
Tinea versicolor
Tinea versicolor is a condition characterized by a rash on the trunk and proximal extremities. Recent research has shown that the majority of Tinea versicolor is caused by the Malassezia globosa fungus, although Malassezia furfur is responsible for a small number of cases...
refers to a fungal infection of the skin caused by Malassezia furfur
Malassezia furfur
Malassezia is a genus of fungi. Malassezia is naturally found on the skin surfaces of many animals, including humans. In occasional opportunistic infections,...
. It appears anywhere on the skin and produces red or gray, scaly patches of itchy skin. Deeper infections may be discoloured, ulcerative and purulent.
A Candida yeast infection can also be identified by a KOH test by taking scrapings from the mouth (oral thrush), vagina (vaginitis
Vaginitis
Vaginitis is an inflammation of the vagina. It can result in discharge, itching and pain, and is often associated with an irritation or infection of the vulva. It is usually due to infection. The three main kinds of vaginitis are bacterial vaginosis , vaginal candidiasis, and trichomoniasis. A...
) and skin (candidiasis
Candidiasis
Thrush redirects here. For the hoof infection see Thrush .Candidiasis or thrush is a fungal infection of any of the Candida species , of which Candida albicans is the most common...
). There are over 40 different fungus species known to cause disease in humans, of which Candida albicans is the most common and most frequently tested for.
Procedure
The KOH test for fungus is conducted on an outpatient basis and patients do not need to prepare in advance.Results are usually available while the patient waits or the next day if sent to a clinical laboratory.
The KOH test procedure may be performed by a physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
, assistant or a nurse. If fungal cultures are required, the test is performed by a technologist who specializes in microbiology.
Skin, nail, or hair samples are collected from the infected area on the patient. For skin samples, a scalpel or edge of a glass slide is used to gently scrape skin scales from the infected area. For hair samples, a forceps is used to remove hair shafts and follicles from the infected site. If the test is being sent to a laboratory, the scrapings are placed in a sterile covered container. For immediate tests, the scrapings are placed directly onto a microscope slide and are covered with 10% or 20% potassium hydroxide.
The slide is left to stand until clear, normally between five and fifteen minutes, in order to dissolve skin cells, hair, and debris. To enhance clearing dimethyl sulfoxide
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
can be added to the slide. To make the fungi easier to see lactophenol cotton blue stain
Stain
A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. Stains are caused by the chemical or physical interaction of two dissimilar materials...
can be added. The slide is gently heated to speed up the action of the KOH. Adding calcofluor white stain to the slide will cause the fungi to become fluorescent, making them easier to identify under a fluorescent microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
.
Evaluation
Dermatophytes are easily recognized under the microscope by their long branch-like tubular structures called hyphae. Fungi causing ringworm infections produce septate (segmented) hyphae. Some show the presence of sporeSpore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s formed directly from the hyphae (arthroconidia). Under the microscope Tinea versicolor is recognized by curved hyphae and round yeast forms that give it a spaghetti-and-meatball appearance.
Yeast cells appear round or oval and budding forms may be seen. The KOH prep cannot identify the specific organism; the specimen can be submitted for fungal culture to identify the organism.
A normal, or negative, KOH test shows no fungi (no dermatophytes or yeast). Dermatophytes or yeast seen on a KOH test indicate the person has a fungal infection. Follow-up tests are usually unnecessary.
The skin may be sore after the test because of the tissue being scraped off the top of the surface of the skin.
External links
- http://candidaandbloating.co.uk/candida-tests/koh-test-for-candida-albicans
- http://medical-dictionary.thefreedictionary.com/KOH+Test
- http://www.medicalhealthtests.com/articles/233/medical-tests/koh-test-for-candida-albicans.html