Smears
must be prepared, labelled and fixed correctly prior to being stained.
Blood Smear:
Blood A blood smear is a differential count of white blood cells and the diagnosis of abnormal forms of leukocytes (toxic neutrophils, left shift, blast cells), erythrocytes (polychromasia, anisocytosis, inclusions, irregular platelets) and platelets (paraplatelets). is a valuable diagnostic tool. , platelet clumps). But to obtain relevant information, a suitable technique is needed for the preparation of a smear, which provides a monolayer of dispersed cells and a cell division that reveals the cell concentration in the blood. An inadequately prepared smear can present different patterns and cause errors in the differential count.
Sample collection:
Blood films should be made immediately after blood collection, as cell morphology deteriorates rapidly after sample collection. EDTA sample or fresh blood immediately from the collection needle, before the anticoagulant can be administered. Heparinized specimens are unusable for smear preparation.
Labeling slides
Each slide should be clearly labeled with the date and the patient's name and number. Whenever possible, smears should be spread on slides with one end cold for labeling. A lead pencil should be used. Staining the stained area because it will not wash off during the staining process. CAUTION: Slides with a positive AFB smear should always be discarded and never reused.
How to make a smear:
Preparation of smear
An area approximately 15-20 mm in diameter should be spread evenly on the slide. Following are the techniques used for making smears from different specimens.
1). Pus sample:
Using a sterile wire loop, create a skinny preparation. Do not centrifuge purulent fluid.
2). Non-purulent fluid sample:
Centrifuge the fluid and smear with a drop of well-mixed sediment.
3). Culture:
Emulsify the colony in sterile distilled water and thin the preparation onto a slide. With the broth culture, transfer a loop to a slide and make a thin preparation.
4) Wholesale:
Use a piece of sterile rod to transfer and spread the pus and caseous material on a slide. Soak the rod in phenol or hypochlorite disinfectant before discarding.
5) Broom:
Roll the broom onto the slide. This is especially important when looking for intracellular bacteria such as N. gonorrhoeae (urinary tract, cervical, or eye swabs). Rolling the swab avoids damaging the pus cells.
6. Stool:
Use a piece of clean swab to transfer the pus and mucus to the slide. Decontaminate the stick before disposing of it. Spread it for thin preparation.
Drying and fixing of smears:
After making the smear, leave the slide to air dry in a safe place, protected from dust. The purpose of fixation is to preserve microorganisms and prevent stains from being washed off the slides during staining. Smears are fixed by heat or alcohol. Microorganisms are not killed by heat fixation, such as M. tuberculosis
Smear microscopy:
Smear stain:
1). Determination of heat:
It is widely used but heat can damage organisms and alter their staining response especially when excessive heat is used. Heat fixation also damages leukocytes and is therefore inappropriate for fixing smears that may contain intracellular organisms such as N. gonorrhoeae and N. meningitidis. When used, heat should be determined with caution. The following techniques are recommended:
1). permit the smear to air dry fully
2). Smear the slide rapidly, from above, three times with the flame of a spirit lamp or the pilot flame of a Bunsen burner.
Note: After passing the slide through the flame three times, it should be possible to feel the hand uncomfortably hot without placing the slide on the back of the hand. When this cannot be done, too much heat is used.
3). permit the smear to chill before staining
2). Determination of alcohol:
This form of fixation is much less harmful to microorganisms than heat. Cells, especially pus cells, are also well preserved. Therefore, alcohol fixation is recommended to fix smears when looking for Gram-negative intracellular diplococci or Mycobacterium tuberculosis.
3). Other chemical modifications:
Other chemicals are sometimes necessary to fix smears containing particularly virulent organisms to ensure that all organisms are killed, such as potassium permanganate, formaldehyde vapor.
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