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Test ID: Gram stain
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Gram stain (Microbiology)
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Examine any sample Microscopically by gram stain
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Useful For
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The demonstration of Gram negative and Gram-positive bacteria.
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Method name and description
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Gram stain. The stain colors some bacteria deep blue (Gram positive) and leaves others either unstained or colored by the counterstain (Gram negative). It is known that the organisms that stain deep blue have a cell wall containing teichoic acid, and those that are unstained or stain red contain lipopolysaccharides.
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Clinical information
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The Gram stain is a general stain used extensively in microbiology for the preliminary differentiation of microbiological organisms. The Gram stain is one of the simplest, least expensive, and most useful of the rapid methods used to identify and classify bacteria.
The Gram stain is used to provide preliminary information concerning the type of organisms present directly from clinical specimens or from growth on culture plates.
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Aliases
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Gram stain (Microbiology)
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Specimen type / Specimen volume / Specimen container
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Specimen type: Smears from clinical specimens
Specimen volume/ Specimen container:
At least 2 smears on 2 clean sterile glass slides.
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Collection instructions / Special Precautions / Timing of collection
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Follow the collection instructions for the relevant specimen type- see under the relevant test in the Lab Guide.
Prepare a thin smear on a clean microscope slide. Prepare a second slide in a similar way.
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Relevant clinical information to be provided
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- Antimicrobial therapy
- Collection site
- Patient clinical condition
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Storage and transport instructions
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Slides should be securely enclosed in a box or petri dish before dispatching them to the Laboratory to avoid any potential contamination.
Slides need to be sent to the Laboratory at room temperature immediately after collection
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Specimen Rejection Criteria
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- Broken slides
- Unlabeled slides with patient/case identification
- Contaminated slides
- No relevant clinical details provided with the request. (Please note that where applicable, the relevant clinical details should reflect those on the patient’s electronic record at the time the order was placed).
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Biological reference intervals and clinical decision values
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Results will be reported based on the:
Gram reaction (Positive /negative)
Cellular morphology (Cocci/ bacilli/ coccobacilli /filamentous)
Arrangement (chains/clusters/diplo/branching).
The report will also include the relative numbers of WBCs, epithelial cells and
any intracellular organisms.
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Factors affecting test performance and result interpretation
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Improper collection.
Use of glass slides that have not been precleaned or are not sterile.
Smear preparations are too thick. Improper techniques such as overly thick smears often produce false results.
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Turnaround time / Days and times test performed / Specimen retention time
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Turnaround time:
STAT: 1 hour
Non-STAT: 24 hours
Days and times test performed:
24/7
Specimen retention time:
7 days after final report
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