What is the role of lab studies in the workup of folliculitis?

Updated: Oct 08, 2020
  • Author: Elizabeth K Satter, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Answer

Laboratory studies are typically not obtained because diagnosis is usually made based on history and physical examination findings alone. In cases resistant to standard therapy, cultures, Gram stain, potassium chloride (KOH) preparation, and biopsy are the diagnostic tests of choice.

Gram stain and bacterial culture are best performed by unroofing an entire pustule with a No. 15 blade and depositing material onto a glass slide and a sterile cotton swab. In typical cases, Gram stain shows gram-positive cocci, and culture grows S aureus. Pseudomonas species can be cultured from the pustules of hot tub folliculitis.

Nasal culture of family members to look for S aureus colonization may be needed in chronic cases.

KOH inspection, fungal culture, or both can be useful for diagnosing dermatophyte infections. Pityrosporum yeast forms are best appreciated on biopsy specimens in cases of Malassezia (Pityrosporum) folliculitis.

Viral culture or biopsy assists in the identification of folliculitis caused by herpes simplex virus.

A small punch biopsy (3-4 mm) of an active lesion should be performed in atypical cases or in patients resistant to standard treatments.

A complete blood cell count often reveals leukocytosis and eosinophilia, with elevated immunoglobulin E levels in patients with eosinophilic folliculitis.


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