A blood count requires more than just counting the numbers of red cells, white cells, and platelets--it also involves identification of the individual white cells and observing the morphology of the red cells and platelets. Although the actual count may be done on an electronic counting instrument, identification and morphology are done by placing a drop of blood on a glass microscope slide and making a smear. The smear is dried and stained, using a Wright's stain, and examined under a microscope.
Things You'll Need
- Microscope slides
- Rubbing alcohol or soap
- Sterile blood lancets or a needle
- 1 staining dish containing Wright's stain
- 1 staining dish containing distilled water
- Paper towel
- Immersion oil
- Reference book
Clean the end of your index finger with rubbing alcohol or soap and water. Make a small puncture at the tip of the index finger using either a sterile blood lancet, if available, or a sterile needle. Place a small drop of blood at one end of a glass microscope slide. Draw the edge of another slide up against the drop of blood at a 30 to 40 degree angle and push the drop of blood down the length of the original slide to make a thin smear or "film." Allow the blood smear to dry.
Immerse the slide with the dried blood smear in the staining dish containing Wright's stain for 15 seconds. Shake off any excess stain and transfer the slide to the staining dish containing distilled water for 30 seconds. Rinse the slide under running water to get rid of excess stain. Blot the bottom and edges of the slide on a paper towel and allow to air dry.
Place a drop of immersion oil on the dry, stained blood smear. Set the slide on the stage of the microscope and secure it between the clips to hold it in place during examination. Turn on the microscope lamp and adjust both the condenser (up--brighter and less contrast or down--darker and more contrast) and the iris diaphragm (open wider for more light or close down for less light) . You will begin your examination under the low-power oil objective, which will be 40, 43, or 45, depending on your microscope.
Swing the low-power oil objective around and lower it using the coarse adjustment knobs on the microscope until it just touches the drop of immersion oil on the slide. Lower the objective into the drop, using the fine adjustment knob. Look into the microscope eyepiece and slowly adjust the focus, using only the fine adjustment knob. Red cells will show up as small, reddish, bi-concave discs--there should be many of them. White blood cells will be larger than red cells, fewer in number, and sprinkled throughout the fields of red cells. White cells generally have a large purple nucleus surrounded by blue, pink, or grayish-blue cytoplasm, depending on which whites are present. Main white cell types you should be able to see will include neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Platelets will show up as small purple spots scattered among the cells.
Once the initial focusing and scanning is done with the low-power oil immersion objective, the high-power oil objective should be carefully rotated into the oil drop on the slide. This objective provides the greatest magnification (95, 97, or 100, depending on your microscope) and is used to examine cells more closely for inclusion bodies, microorganisms, and structural abnormalities. Only minor focusing adjustments should need to be made--and only with the fine adjustment knob. You may need to make adjustments to the light source to facilitate viewing--raising the condenser and opening the iris diaphragm will provide a brighter image.
After the blood slide has been examined, rotate the low-power objective into position, remove the slide from the microscope stage, and wipe all traces of oil from the lenses and from the microscope stage.