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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 in tissue.
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Method name and description
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Gram stain. The stain colors some bacteria deep blue (Gram+) and leaves others either unstained or colored by the counterstain (Gram-). 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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Specimen type / Specimen volume / Specimen container
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Specimen type: Any well-fixed tissue in 10% neutral buffered formalin.
Specimen volume/ Specimen container: Submit 3-4 µm paraffin embedded tissue section mounted on a clean glass slide.
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Collection instructions / Special Precautions / Timing of collection
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Collection instructions / Special Precautions:
- Aseptic technique should be followed
Timing of collection:
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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 are stored in slide box at room temperature.
- Follow your local regulation shipping guidelines.
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Specimen Rejection Criteria
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- Broken slides
- Unlabeled slides with patient/case identification
- Contaminated slides
- Slides/Paraffin blocks mismatch
- 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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- Prepare a thin smear on a clean microscope slide for Gram staining after performing culture. Refer to stains SOP
- Record the relative numbers of WBCs, epithelial cells, bacterial and fungal morphotypes. Note intracellular organisms.
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+
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Scanty/(Few)
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1-4 per oil immersion field
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< 10 / lpf
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++
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Moderate
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5-10 per oil immersion field
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10-25/lpf
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+++
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Profuse
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> 10 per immersion field
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>25 /lpf
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Factors affecting test performance and result interpretation
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- Specimen fixation. Well-fixed specimens can produce consistent chemical and physical characteristics in tissue sections which allows patterns to be observed, morphological and chemical changes to be noted and comparisons made.
- Smear thickness
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Turnaround time / Days and times test performed / Specimen retention time
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Turnaround time: 3 hours
Days and times test performed: Once daily (Sunday to Thursday @0700-1500)
Note: Request received after 1100H will be run/stained the following working day.
Specimen retention time: 10 years
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