Microbiology Test

Methylene blue stain

Dr. Nithin Jayan
Medically Reviewed by Dr. Nithin Jayan, MBBS, DNB
Last Updated on Apr 18, 2014
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Test : Methylene blue stain

Indications : The presence of leukocytes in stool indicates inflammatory diarrhea and it is this feature that forms the basis of the methylene blue test.

Stool sample is collected in a sterile container. Care must be taken to see that the sample is not contaminated with urine, water, pubic hair or any other body tissue.

Stool analysis can be carried out inexpensively and effectively by using stains such as methylene blue or Wright’s stain. One drop of saline is added to a small sample of stool. A small portion of the sample is placed on a micro slide, stained with methylene blue and observed directly under a microscope.

No preparation is required prior to the test.

Physiology : Methylene blue is a redox indicator that turns blue in an oxidized state and becomes colorless in a reduced state. In room temperature methylene blue appears as an odorless dark green powder and is quite different from ‘methyl blue’. Methylene blue can be used as a dye, reagent and a laboratory indicator.

The methylene blue test is ordered to carry out differential diagnosis of the various types of diarrheal diseases.

Normal Range : No presence of yeast, cocci in clusters or leukocytes

Interpretation : Normal

Absence of leukocytes in stool.

Abnormal

Fecal leukocytes can be observed in those with the following conditions -

Salmonella infections
Shingella infections
Ulcerative colitis
Crohn’s disease

Leukocytes will be absent in fecal samples from those with Giardia, E.coli or viral infections and also in cases of food poisoning.

Once the cause of the diarrhea or gastroenteritis is identified, efficient treatment may be initiated.

Sample : Fresh random stool, rectal swab

Test Method : smear of stool with one drop of methylene blue, coverslip and observe the presence of leukocyte.

Related Tests : Stool culture, Clostridium difficile Toxin assay



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