Otitis externa laboratory findings

Laboratory findings consistent with diagnosis of all forms of otitis externa include evidence of bacterial or fungal infection. Findings may also include markers of inflammation such as an elevated erythrocyte sedimentation rate, C-reactive protein, and elevated white blood cell count.

Otitis externa from a suspected bacterial infection may be determined by the following tests:

• Culture of the ear canal to determine if the infection is caused by Pseudomonas aeruginosa or Staphylococcus aureus.^[1]
  • • This test will be performed in the event that the symptoms do not resolve with the treatment and the otitis externa becomes recurrent.
• Gram stain test: If the cause is determined to be bacterial, the gram-stain test will determine whether the cause is Psuedomonas aeruginosa (Gram negative) or Staphylococcus aureus (Gram positive):^[2]
• Real-time polymerase chain reaction to detect and determine the exact bacterial pathogen^[3][4]

Otitis externa from a suspected fungal infection will be determined by the following tests:

• Culture of the ear canal to determine if the infection is caused by Aspergillus niger, Aspergillus fumigatus, or Candida albicans^[5]
  • Immunofluorescent microscopy may reveal the following results:^[6]
  • Fungal hyphae
  • Arthrospores
  • Arthroconidia
• Real-time polymerase chain reaction to detect and determine the exact fungal pathogen.^[7]

• A complete blood count test performed on otitis externa patients may reveal abnormal white blood cell counts.

Otitis externa patients may display the following findings on inflammatory marker tests:

• Erythrocyte sedimentation rate and CRP are commonly elevated in cases of malignant necrotizing otitis externa^[8]

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