Part II: Microscopy
laboratory layout and equipment

Plan of a peripheral microscopy laboratory
Ideally, tuberculosis microscopy should be done in a separate room. However, tuberculosis microscopy services are usually integrated in general laboratory diagnostic services of countries, which makes the design of a dedicated tuberculosis microscopy laboratory difficult. Nevertheless, in integrated laboratories a separate area should be reserved for tuberculosis microscopy. Enough space should be provided. Walls, ceilings and floors should be smooth, non-absorbent, easy to clean and disinfect and resistant to the chemicals used for microscopy. Floors should be slip resistant and lighting should be adequate. The microscopy area should contain three distinct sections, as illustrated in Figure 1:

• one area for the receipt of specimens, for completing the laboratory register and for storage
• one well-lit area for preparing and staining smears
• one area for microscopy

The laboratory should contain at least four benches or tables, as indicated in Figure 1:

• one bench for smear-preparation
• one bench for staining (preferably containing a staining sink)
• one bench for microscopic examination. If there is no electricity, this should be  directly in front of a window
• one bench for receipt of specimens, laboratory registers and slide storage

Bench tops should be wide, the correct height for work at a comfortable sitting position, smooth, easy to clean and disinfect and resistant to the chemicals used. Adequate storage facilities should be provided.

Access to the laboratory should be restricted to authorised persons. Entry to the laboratory is via a single door which should always be closed. Specimens arriving at the laboratory are presented through a window/hatch to a separate reception bench. Here, specimen containers are checked for leakage and their surfaces decontaminated. Cross-checking of laboratory request forms against specimens is also done and the relevant details are entered into the laboratory register. On completion of these activities the specimens are passed into the main laboratoryarea for further processing. The main laboratory area contains all the facilities necessary for smear preparation. This area houses work benches, a wash basin and storage cabinets. The reading area is reserved for performing microscopy and contains work benches, a microscope and a wash basin (optional). Laboratory reports are completed here and passed to the reception bench where the laboratory register is completed and the results despatched.

Arranging equipment and materials
Before the preparation of smears is started, equipment and materials should be arranged to ensure a logical and safe flow of work. All manipulations in preparing smears should be standardised and the arrangement of materials should always be the same to ensure maximum safety, as illustrated by Figure 2. For left-handed technicians it may be more convenient to arrange all or most items in the opposite direction, ie. in a mirror-image.

Care and maintenance of essential equipment
Annex 1 contains a list of essential equipment and supplies for a peripheral laboratory performing Ziehl-Neelsen microscopy. Before purchasing new equipment and supplies it is worthwhile to obtain personal advice of laboratory persons who have had experience in their use. Do not rely entirely on advertisements, catalogues, extravagant claims of sales representatives and the opinion of purchasing officers.

Microscope
The microscope is a precision instrument and requires careful maintenance from both the optical and the mechanical points of view. Laboratory workers should be familiar with the general mechanical and optical principles. Detailed knowledge is unnecessary and apart from basic principles on care, maintenance should be left to professionals. Most manufacturers publish manuals containing useful explanations and information.

• When not in use, the microscope should be kept in its case or protected from dust by a plastic cover
• Avoid exposing the microscope to moisture. Humidity may allow fungi to grow on the lenses and may cause rusting of the metal components. To limit exposure to moisture, place a shallow plate containing dry blue silica gel in the microscope case whenever the microscope is stored. When silica gel is unable to absorb more moisture it changes colour (from blue to pink). In such situations the silica gel could be replaced or dehydrated in  a hot air oven and re-used when its original (blue) colour reappears
• To remove a slight film of fungi, moisten a wad of cotton wool with appropriate fungal cleaner and clean the lens by moving the cotton around in circles using moderate pressure. If necessary, repeat with a fresh wad of cotton wool. Wipe the lens with lens tissue
• Avoid keeping the microscope in a place where there are chemical reagents, water or discharges of corrosive gas
• The microscope should be picked up or carried with two hands, one grasping the arm firmly and the other under the base for added support. Never carry a microscope with only  one hand
• Install the microscope on a sturdy, level surface. Do not place equipment and  instruments generating vibrations (eg. centrifuges) on the same table
• If the microscope is to be used every day, do not remove it from the site of  installation, but when not in use keep it covered with a polythene or plastic cover
• Microscope lenses may be scratched by dirt or grit. The lenses should be cleaned only with clean, dry lens tissue. Cloth or other tissues should not be used as they may scratch the lenses. Never use soap, alcohol, or other solvents to clean the lenses
• Immersion oil must not be allowed to fall on the stage. Immersion oil should be wiped  from the objective lenses after each slide to avoid cross-contamination
• Care must be taken that objectives for dry use do not touch the immersion oil. Should  this happen, clean immediately
• The microscope should never be dismantled; if faulty it should be entrusted to a competent person for repair

Balance
The balance is a fragile and precision instrument and must be used with care. Always consult the accompanying manual for detailed operating instructions.

• Always keep the balance and weights clean and dry to protect them from corrosion. Any  change in the surface of the parts may affect the accuracy of the balance
• Do not put material to be weighed directly on the pan; always use a container or weighing paper. Subtract the weight of the container or weighing paper from the combined weight of the container and material weighed
• Protect the balance from drafts of air. Air moving cross the pans will cause an inaccurate reading. The more accurate balances have individual cases which are to be closed at the final reading
• Do not return unused substances to the stock bottle to prevent contamination of stock materials