KOH test

Alternative names
Sputum smear; Fungal smear

Sputum smear (KOH test) is a test for the presence of fungal microorganisms in sputum.

How the test is performed
Obtain a sputum sample by coughing deeply and expelling the material that comes from the lungs (sputum) into a specimen container. A smear of sputum is prepared with potassium hydroxide (KOH) and examined under the microscope. If it is positive, fungal cells can be observed.

How to prepare for the test
There is no special preparation.

How the test will feel
There is no discomfort.

Why the test is performed
The test may be performed when there is abnormal sputum production or when an infection of the lungs is suspected.

Normal Values
No presence of organisms is normal.

What abnormal results mean
Abnormal results indicate the presence of fungus such as histoplasmosis, coccidioidomycosis, or blastomycoses. White blood cells called eosinophils may also be present.

Additional conditions under which the test may be performed:

  • Acute pulmonary eosinophilia (Loeffler’s syndrome)  
  • Coccidioidomycosis; acute (primary) pulmonary  
  • Coccidioidomycosis; disseminated

What the risks are
There are no risks.

Special considerations
Not applicable.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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