Otitis externa laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Luke Rusowicz-Orazem, B.S.
Overview
Laboratory findings consistent with diagnosis of all forms of otitis externa include evidence of bacterial or fungal infection. They also include markers of inflammation, such as an elevated Erythrocyte sedimentation rate and C-reactive protein, as well as elevated white blood cell count.
Laboratory Findings
Bacterial
- Otitis externa from a suspected bacterial infection will be determined by the following tests:
- Swab 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 Pseudomonas aeruginosa or Staphylococcus aureus:[2]
- Results are purple: indicates that the culture is gram-positive and is indicative of Staphylococcus aureus.
- Results that are red: indicates that the culture is gram-negative and is indicative of Pseudomonas aeruginosa.
- Real-time polymerase chain reaction to detect and determine the exact bacterial pathogen.[3]
- Results indicative of Pseudomonas aeruginosa or Staphylococcus aureus include DNA samples from either pathogen.[4]
- Swab of the ear canal to determine if the infection is caused by Pseudomonas aeruginosa or Staphylococcus aureus.[1]
Fungal
- Otitis externa from a suspected fungal infection will be determined by the following tests:
- Swab of the ear canal to determine if the infection is caused by Aspergillus niger, Aspergillus fumigatus, or Candida albicans.[5]
- A fungal culture will be collected to cultivate spores for observation, determining the specific pathogenic fungus.
- 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]
- Results indicative of Aspergillus niger or Candida albicans include DNA samples from either pathogen.
Common Findings
- White Blood Cell Count
- A complete blood count test performed on otitis externa patients may reveal abnormal lymphocyte and other white blood cell counts, lesser or greater than normal.
- Markers for Inflammation
- Otitis externa patients may display markers for inflammation, determined by the following tests:
- Erythrocyte sedimentation rate - this is usually abnormally elevated in cases of malignant necrotizing otitis externa.[8]
- C-reactive protein
- Otitis externa patients may display markers for inflammation, determined by the following tests:
References
- ↑ Llor, C.; McNulty, C. A. M.; Butler, C. C. (2014). "Ordering and interpreting ear swabs in otitis externa". BMJ. 349 (sep01 2): g5259–g5259. doi:10.1136/bmj.g5259. ISSN 1756-1833.
- ↑ Beveridge TJ (2001). "Use of the gram stain in microbiology". Biotech Histochem. 76 (3): 111–8. PMID 11475313.
- ↑ Khan AA, Cerniglia CE (1994). "Detection of Pseudomonas aeruginosa from clinical and environmental samples by amplification of the exotoxin A gene using PCR". Appl. Environ. Microbiol. 60 (10): 3739–45. PMC 201881. PMID 7986047.
- ↑ Brakstad OG, Aasbakk K, Maeland JA (1992). "Detection of Staphylococcus aureus by polymerase chain reaction amplification of the nuc gene". J. Clin. Microbiol. 30 (7): 1654–60. PMC 265359. PMID 1629319.
- ↑ Kaur R, Mittal N, Kakkar M, Aggarwal AK, Mathur MD (2000). "Otomycosis: a clinicomycologic study". Ear Nose Throat J. 79 (8): 606–9. PMID 10969470.
- ↑ "Aspergillus Otomycosis | Aspergillus & Aspergillosis Website".
- ↑ Van Burik JA, Myerson D, Schreckhise RW, Bowden RA (1998). "Panfungal PCR assay for detection of fungal infection in human blood specimens". J. Clin. Microbiol. 36 (5): 1169–75. PMC 104793. PMID 9574670.
- ↑ Bovo R, Benatti A, Ciorba A, Libanore M, Borrelli M, Martini A (2012). "Pseudomonas and Aspergillus interaction in malignant external otitis: risk of treatment failure". Acta Otorhinolaryngol Ital. 32 (6): 416–9. PMC 3552534. PMID 23349563.