Microscope Use—cont’d

Chapter 6 Laboratory Equipment 101

11. While looking through the eyepieces, slowly turn

the coarse adjustment knob until the specimen comes into approximate focus. It may not be possible to bring the specimen into complete focus using only the coarse adjustment knob.

12. Without moving the slide or the objective, use the

fine adjustment knob to bring the specimen into complete focus.

13. Adjust the amount of light entering the specimen

by moving the condenser down and by adjusting the diaphragm until the specimen appears in crisp, clear focus.

14. Use the stage adjustment knob to move the object

viewed directly into the center of the field of vision while looking in the microscope.

15. Use the nosepiece to swing the next objective so

that it is pointing directly down at the slide. As before, the objective should click into place.

16. Use the fine adjustment knob to bring the object

into focus. It may be necessary to adjust the amount of light entering the specimen to see the object clearly.

17. If desired for the type of specimen viewed,

continue this process, using the fine focus and adjusting the available light as the objectives are changed to higher levels of magnification.

18. If the oil immersion lens (the lens marked with

the 100X and a ⬁ symbol) is to be used, it will be necessary to place one or two drops of immersion oil on the slide before rotating the objective into place.

a. Use the nosepiece to move the current objective

out of the way, but do not lower the 100X objective until the oil has been added.

b. Keep the slide as it was with the previous objec-

tive and place the drop(s) of oil on the slide right over the light source.

c. Then, use the nosepiece to lower the 100X lens

into place and adjust the focus as needed with the fine adjustment knob.

The coarse adjustment knob allows for an approximate focus.

The fine adjustment knob is to be used only after approximate focus has been accomplished with the coarse adjustment knob.

Too much light at a low magnification may cause the specimen to appear washed out, and some of the formed elements may be overlooked. Too little light does not allow for enough contrast to identify some of the structures.

If this step is not performed, you may not be able to find the object again after changing to the next level of magnification, especially if the specimen only covers a small portion of the slide.

Always watch the objective as you move it into place to avoid touching anything with the objective lens. With the objectives above 10X, do not use the coarse

adjustment knob for focus.

Some specimens do not require higher levels of magni- fication if the structures can be identified at the lower levels.

Resist the urge to make more room for this objective before moving it into place. This objective will be very close to the slide; it will appear that it is going to touch the slide, but if the proceeding steps were performed correctly, it will not touch the slide. The oil will seal the objective with the slide to keep the light focused on the specimen with clarity.

Procedure Rationale

Test Your Knowledge 6-6

Which adjustment knob should be used first when the specimen on the microscope is initially brought into focus?

(Outcome 6-5)

19. After the specimen has been analyzed as needed,

lower the stage to the lowest possible point, and remove the slide from the stage clips.

20. Using the nosepiece, adjust the objectives so that

the lowest power is pointing down toward the stage.

21. Turn off the light source, and clean the eyepieces

and objectives using lens paper. Remember to clean the 100X objective last, if applicable. Xylene can be used on the lens paper if needed for exces- sive soiling of the lenses.

22. Wipe off the stage and the rest of the microscope

using a laboratory tissue such as Kimwipes. Mois- ten the tissue if necessary to remove dust. The stage should be disinfected periodically by using an alcohol wipe.

23. Unplug and secure the electrical cord, and put the

plastic cover back on the microscope. Be certain to move the microscope to the appropriate storage area as directed by office policy.

24. Discard the slide or place it in the appropriate

storage area as dictated by office policy.

25. Remove gloves (if used for the procedure) and

wash hands.

The stage should always be at the lowest point during storage to avoid potentially damaging the objectives. This allows the focusing to start appropriately when a new slide is put on the microscope, and also helps to avoid potential damage to the objectives.

Only lens paper should be used for this, as any other type of tissue will scratch the sensitive lenses. If the 100X objective is cleaned first, the rest of the lenses may be contaminated with oil.

If xylene is used, be sure to follow appropriate protec- tive measures as described by the manufacturer and the workplace.

The slides, specimens, and oil can easily soil the stage.

Be sure to use two hands when transporting the microscope.

Stained specimens are often stored for a period of time for future study. Slides should be treated as a “sharp” and disposed of in a puncture-resistant biohazard container.

Hands should be washed before and after each proce- dure in the laboratory setting.

Procedure 6-1: Microscope Use—cont’d

Test Your Knowledge 6-7

Is the microscope stage moved when objectives are changed for higher magnification of a specimen?

(Outcome 6-5)

Other Types of Microscopes

A dissecting microscope may also be utilized in the laboratory to view specimens that need to be seen in their natural state without compression or those that are too thick to be viewed effectively with the compound microscope. This type of microscope may also be known as a stereo microscope because the microscope is designed to allow a slightly different view from each of the eyepieces, providing an image with depth and dimension. The light source for this type of microscope is not focused in the same way that the compound microscope is focused; it is diffused or reflected onto the

image rather than shone directly through it. The magni- fication ability of the dissecting microscope is not as extensive as that of the compound microscope, as it is usually only capable of enlarging the specimen by 40 or 100 times its normal size. Dissecting microscopes are often used for blood bank procedures when the technol- ogist is examining different serum and cell combinations to look for agglutination of the specimen. Dissecting microscopes may be used for a variety of other purposes in the clinical laboratory when fine, detailed work needs to be performed with some magnification.

An electron microscope allows for much greater mag- nification of specimens, and also provides a three dimen- sional image. Electrons are utilized to “excite” the speci- men, and the resulting interaction with the atoms present in the specimen will produce an image to be recorded and studied. This image is more of a picture that is defined by the properties of the specimen, rather than a true image seen by the eyes while viewing the specimen. The image created by the excitation of the sample is stored and viewed on a computer. Electron microscopes may be used to visualize specimens that are far too small to be seen with a compound microscope, such as viruses and the interior structures of cells. This type of microscope is not routinely found in clinical laboratories, as the user requires specialized training to operate it and interpret the images created with examination.

How Do Medical Assistants Use Microscopes? The majority of the time, a medical assistant will not perform microscopic examinations for diagnostic pur- poses. There are a few microscopic procedures that have been classified as CLIA moderately complex procedures, and these can be performed by medical assistants with appropriate documented training. These include urine microscopic analysis (see Chapter 22) and normal blood cell differential counts (see Chapter 12). These are the exceptional cases in specialized offices such as urology offices or physician office laboratories with minimal staffing. Most commonly, a medical assistant’s use of a microscope is limited to focusing the specimen for the health-care provider, as well as performing maintenance procedures. It is of great benefit for a medical assistant to

Chapter 6 Laboratory Equipment 103

Test Your Knowledge 6-8

What type of microscope may be used to see viruses? a. Compound microscope

b. Electron microscope c. Dissecting microscope

d. Fluorescent microscope (Outcome 6-2)

be capable of focusing the microscope, as this allows the health-care provider’s valuable time to be spent examin- ing the specimen rather than performing the original setup process. Medical assistants may be focusing stained blood smears, urinalysis sediment specimens, vaginal smears, nasal smears, Gram-stained microbiological specimens, and microscopic examinations for the pres- ence of fungal elements on the microscope for examina- tion. Remember, if the health-care provider does per- form microscopy examinations, the laboratory must register as a CLIA site that provides this type of service.

Centrifuges

A centrifuge is an instrument used to prepare blood (or other liquid specimens) for transport or testing. Blood is made up of cells that are suspended in a liquid substance called plasma. Chemical analysis is often performed on the plasma, and in order for the results to be accurate, the cells must be removed from the liquid portion of the blood as soon as possible after the specimen is obtained. A centrifuge is used to force the separation of the cells from the fluid portion of the blood (plasma).

If a blood specimen is allowed to sit for an extended period of time in a tube, gravity causes the cells to settle to the bottom of the tube, as they are denser (heavier) than the surrounding fluid. A centrifuge creates a pow- erful “artificial” gravity source, called centrifugal force. The force is formed as the specimen spins around an axis hundreds to thousands of times per minute. When a specimen is processed by a centrifuge, the separation of the different components of the blood is accelerated; the cells are pushed to the bottom of the tube within minutes. This allows the plasma to be removed from the cells in a timely manner so that chemical analysis can be performed. Urine specimens may also be centrifuged to bring the suspended elements (such as blood cells, bacteria, etc.) to the bottom of the tube so that they can be examined under a microscope.

There are various types of centrifuges available for use in a laboratory. Some of the benchtop models are designed to spin 8 to 10 samples at a time for a maxi- mum of 10 minutes each cycle. Others are units the size of a dishwasher, capable of processing hundreds of tubes in each cycle for extended periods of time. The decision about which type of centrifuge to use is based on several

Test Your Knowledge 6-9

Is a medical assistant properly trained to perform microscopic identification procedures? (Outcome 6-6)

factors, including the volume of samples to be processed, the requirements for the liquid portion of the blood after separation, and the amount of separation required. The decision may also be based on the recommended maintenance procedures for the centrifuge model of choice, as well as cost. Some centrifuges generate a lot of excess heat as they operate, due to the rapid turning of the unit around the axis. These models require built-in refrigeration to decrease the temperature to keep the specimens from becoming overheated.

Centrifuge Maintenance

Maintenance of all centrifuge models is similar. It is important that the interior and exterior of the machine stay clean and that there is nothing impeding the rotation of the unit around the axis. The rotations per minute

(rpms) must also be checked at least quarterly using a tachometer. If the rotations have changed significantly

since the last check, the instrument should be serviced, as there may be a problem that needs to be addressed. Many centrifuge models have a brushed drive motor, and these brushes must be changed at intervals recommended by the manufacturer. All metal components of the centrifuge should be checked for cracks at least once a month. As with all electrical equipment, the electrical cord should also be checked for wear periodically.

Centrifuge Safety

• All medical centrifuges should have a cover that must be locked in place when in operation. Figure 6-2 shows an example of a centrifuge. The cover keeps the operator safe from potential aerosol formation or splashing that may occur if a specimen breaks or if a tube becomes uncovered during the cycle.

• It is also important that the centrifuge is balanced before starting. This means that for every tube inserted into the centrifuge, a tube with the same weight of fluid must be placed directly across from it in the unit. This additional tube may be filled with the same fluid as the specimen (another blood tube filled to the same level, for example), or it may be a balance tube that is filled with the same amount of water. This is a crit- ical step, no matter what type of specimen is to be centrifuged. If the unit is not balanced, it is possible that the centrifuge will rock while operating (like an

off-balanced washing machine), fall off the counter- top, and break the specimens as they are spinning.

• Be certain that all specimens are capped securely before starting the centrifuge.

• It is very important to follow the manufacturer’s recommendations concerning length of cycles and specific maintenance.

• Remember never to open the centrifuge before it stops spinning completely. Never use your hand to try and slow down the final spin; this can be very dangerous.

Test Your Knowledge 6-10

List two maintenance procedures to be performed on a

centrifuge. (Outcome 6-7)

Figure 6-2 The inside (A) and outside (B) of a typical benchtop centrifuge.

A

B

Test Your Knowledge 6-11

What does it mean to balance a centrifuge?

Chapter 6 Laboratory Equipment 105