Alopecia diagnostic study of choice
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The diagnostic test of choice varies with the cause of alopecia. Biopsy, laboratory tests, trichoscopy, and hair pull test are some of the techniques used in diagnosis. Chest X-ray and MRI can be used in mycosis fungoides staging and is useful for alopecia mucinosa while microscopic testing and Wood's lamp is useful for the diagnosis of fungal infection.
Diagnostic Test of Choice
Hair Pull Test
Test for excessive shedding, it is not diagnostic of a particular hair loss but indicates active hair loss is occurring. Hair should not be washed 24-48 hours prior to a hair pull test. It is performed by gently grasping 40-60 hairs and gently pull upward from different parts of the scalp. A positive test is when three to six or more strands are pulled out. The pull test is positive in:
- androgenetic alopecia
- alopecia areata and scarring alopecia
- telogen effluvium
- anagen effluvium
- loose anagen syndrome
Evaluation of the pulled hair may uncover vital information. For example, if the bulb of the hair is dark, it indicates that the hair is in the anagen phase, or if it is white, it indicates that the hair is in the telogen phase.
This is a noninvasive method of examining hair and scalp. The test may be performed with the use of a dermoscope or a video dermoscope.  The Alopecia Areata Predictive Score makes use of it to predict the treatment outcome in patients with patchy alopecia areata. 
A biopsy will reveal the most information regarding hair loss.
Autoantibodies, thyroid function test, ovarian hormones, free testosterone and total testosterone, luteinizing hormone, follicular stimulating hormone, complete blood count and iron panel may be useful in diagnosis.
Potassium hydroxide preparation and fungal cultures can be used in the diagnosis of tinea capitis.
Wood's light can be used in diagnosis of tinea capitis. Majority of Microsporum spp will appear bluish-green, occasionally dull yellow (Microsporum gypseum) and dull blue (Trichophyton schoenleinii). However, in the U.S., under 5% of cases will show fluorescence. 
- Rudnicka L, Olszewska M, Rakowska A, Kowalska-Oledzka E, Slowinska M (2008). "Trichoscopy: a new method for diagnosing hair loss". J Drugs Dermatol. 7 (7): 651–4. PMID 18664157.
- Waśkiel-Burnat A, Rakowska A, Sikora M, Olszewska M, Rudnicka L (2020) Alopecia areata predictive score: A new trichoscopy-based tool to predict treatment outcome in patients with patchy alopecia areata. J Cosmet Dermatol 19 (3):746-751. DOI:10.1111/jocd.13064 PMID: 31301100
- Ponka D, Baddar F (2012). "Wood lamp examination". Can Fam Physician. 58 (9): 976. PMC 3440273. PMID 22972730.