Culture - ear drainage

Alternative names
Ear drainage culture

Definition
Ear drainage culture is a laboratory test to identify organisms that cause ear infections.

How the test is performed

A sample of ear drainage either from the outer ear or middle ear is placed on culture media for the purpose of growing microorganisms (bacteria, fungus, or viruses) in the laboratory, which will later be identified.

The microbiologist inspects the cultures daily for growth. If microorganisms are detected, other tests may be initiated to determine the sensitivity of the organism to medications (sensitivity analysis). Antibiotic therapy can then be determined based on these results.

How to prepare for the test
There is no preparation.

How the test will feel

The specimen will be collected from a cotton swab placed gently inside the outer ear canal. No pain is associated with the test. However, ear pain may be present already if infection is suspected.

If a myringotomy (surgical opening of the eardrum) is performed for relief of a painful, bulging tympanic membrane in otitis media, fluid will be collected at this time. Rarely, a needle may be inserted through the tympanic membrane (eardrum) to obtain a sample of the fluid from the middle ear.

Why the test is performed
The test may be performed for an infection of the outer ear (see otitis externa - acute), as a routine part of myringotomy, otitis media with ruptured eardrum and draining fluid, or otitis media not responding to treatment. Most ear infections are diagnosed by clinical symptoms rather than by obtaining a culture.

Normal Values
No organisms seen on the culture is normal.

What abnormal results mean
Abnormal results indicate infection. The infection may be bacterial, viral, or fungal. The causative organism and an effective medication to treat the organism, if available, may be indicated in the results.

What the risks are
No risks are involved with swabbing the ear canal. Risks of myringotomy and needle aspiration include bleeding, infection, and hearing loss.

Special considerations
Sometimes special stains of the fluid, such as a Gram stain or KOH stain, are done to help with the initial diagnosis.

Johns Hopkins patient information

Last revised: December 5, 2012
by Potos A. Aagen, M.D.

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