What is a Sputum Gram Stain?
A sputum Gram stain is a microscopic test used to differentiate bacteria in liquid sputum samples. The test relies on the principle that bacteria have different stain retention and release properties. The test is used to identify the type of bacteria present, but does not provide information about the number of bacteria.
Preparation
In order to carry out a sputum Gram stain, a sample of sputum must first be collected. The sample must be collected from the area of infection (usually from the throat or lungs). The sample must then be mixed with an appropriate liquid or gel preparation medium prior to processing.
Procedure
The sputum sample is first smeared onto a glass slide and air-dried. Once dry, the slide is flooded with an ethanol-iodine solution which is then removed. The slide is then flooded with a crystal violet dye which stains any bacteria present. The slide is then flooded with a Gram’s iodine solution which acts as a mordant (fixative) for the crystal violet dye. The iodine solution is then removed and the slide is flooded with a decolorizing agent (E.g. acetone-alcohol). This agent removes the crystal violet dye from some bacterial cells, leaving them unstained. The slide is then flooded with a safranin counterstain and allowed to dry. Lastly, the slide is observed under a microscope.
Types
The results of the sputum Gram stain are reported as either positive or negative. A positive result indicates that bacteria are present in the sputum sample. The specific type of bacteria present can then be identified by looking at the stained cells. A negative result indicates that no bacteria are present.
Risks
The risks associated with sputum Gram staining are minimal. However, it is important that the sputum sample is correctly collected and prepared before the test is performed. This is to ensure that accurate results are obtained.
Why is it done?
A sputum Gram stain is usually performed when a patient is suspected of having an infection. It is used to identify the type of bacteria present in the sputum sample, which can then be used to guide treatment.
When is it done?
A sputum Gram stain is typically ordered when a patient is suspected of having a bacterial infection. It can also be used to monitor the effectiveness of a treatment regimen.