Quality assurance in the laboratory

Quality assurance in the laboratory includes all aspects of the analytical work, from correct identification and preparation of the patient to ensuring that the laboratory result goes back to the doctor.

The prime objective of quality assurance is to ensure that the laboratory provides results that are correct and relevant to the clinical situation of the patient.

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Safety in the laboratory

● Each laboratory should have a written manual of safe laboratory practices which should be followed at all times.

● The laboratory should have a first-aid box (see section 3.8.2) and at least one staff member trained in first aid.

● The laboratory should be a work area only; visitors should be restricted.

● No food or drink should be consumed in the laboratory.

● Wear protective clothing and remove it before leaving the laboratory.

● Always consider any laboratory specimen as potentially infectious and handle it carefully; wear protective gloves.

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Dispatch of specimens to a reference laboratory

The peripheral laboratory sends specimens to reference laboratories or more specialized laboratories for examinations that cannot be carried out locally. For example, serological examinations for treponemal infection or typhoid; culture of stools for detection of cholera vibrio; and histological examination of biopsy material.

Table 3.2 shows, for each type of specimen and each examination:

— which container and preservative (where necessary) to use;

— how much of the specimen to send;

— how long the specimen will keep.

1. Packing specimens for dispatch 

Always observe the regulations in force in your country. 

Double pack specimens. Place the specimen in the bottle or tube and seal her- metically (fixing the stopper with sticking-plaster; see Fig. 3.73). 

Check that the bottle is labelled with the patient’s name and the date of collection of the specimen. Then place the sealed bottle in an aluminium tube with a screw cap. Wedge it in the tube with absorbent cotton wool. 

Wrap the request form around the metal tube (Fig. 3.74). It should show: 

— the patient’s name (written in capital letters) and date of birth; 

— the nature of the specimen; 

— the date of collection of the specimen;

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Disposal of laboratory waste

1. Disposal of specimens and contaminated material 

Any clinical material brought into the laboratory and any apparatus used to handle this material must be considered as infectious. To avoid laboratory accidents, make sure that priority is given to correct handling and disposal of specimens and contaminated material. 

2. Incineration of disposable materials 

Making an incinerator (Fig. 3.70) 

An old metal drum is suitable for this purpose. 

1. Fix a strong metal grating (G) firmly about one-third of the way up the drum. 

2. Cut a wide opening or vent (V) below the level of the grating. 

3. Find a removable lid (L) for the drum.

Using an incinerator 

● At the end of each morning’s and each afternoon’s work, place all used stool and sputum boxes on the grating of the incinerator (Fig. 3.71).

Fig. 3.70 Components of an incinerator G: metal grating; L: lid; V: vent.

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Cleaning, disinfection and sterilization in the laboratory

1. Cleaning glassware and reusable syringes and needles

Instructions for cleaning:

— glass containers (Erlenmeyer flasks, beakers, test-tubes)

— pipettes

— microscope slides

— coverslips

— reusable syringes and needles.

Glass containers

New glassware

Glassware that has never been used may be slightly alkaline. In order to neutralize it:

● Prepare a bowl containing 3 litres of water and 60 ml of concentrated hydrochlo- ric acid (i.e. a 2% solution of acid).

● Leave the new glassware completely immersed in this solution for 24 hours.

● Rinse twice with ordinary water and once with demineralized water.

● Dry.

Dirty glassware

Preliminary rinsing

Rinse twice in cold or lukewarm water (never rinse bloodstained tubes in hot water).

If the glassware has been used for fluids containing protein, it should be rinsed immediately and then washed (never allow it to dry before rinsing).

Soaking in detergent solution

Prepare a bowl of water mixed with washing powder or liquid detergent. Put the rinsed glassware in the bowl and brush the inside of the containers with a test-tube brush (Fig. 3.57). Leave to soak for 2–3 hours.

 

Fig. 3.57 Cleaning dirty glassware

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Measurement and dispensing of liquids

Many of the liquids handled in the laboratory are either infectious, corrosive or poisonous. It is important for the prevention of accidents that the correct procedures for the measurement and dispensing of these liquids are clearly under- stood and are followed conscientiously.

Many of the new procedures for analysis require very small volumes of fluid and various pipetting and dispensing devices are available to enable small volumes to be measured with great precision.

Large volumes can be measured using a measuring cylinder or a volumetric flask. A measuring cylinder measures various volumes of fluid but is not very accurate. A volumetric flask measures a single volume of fluid, e.g. 1 litre, accurately.

Small volumes of fluid (0.1–10 ml) can be dispensed rapidly and accurately using one of the following methods:

● A fixed or variable volume dispenser attached to a reservoir made of glass or polypropylene. Various volumes from 0.1 to 1.0 ml and from 2.0 to 10.0 ml can be dispensed.

● A calibrated pipette with a rubber safety bulb.

1. Pipettes 

Types of pipette 

Graduated pipettes

Graduated pipettes have the following information marked at the top (Fig. 3.44):

— the total volume that can be measured;

— the volume between two consecutive graduation marks. There are two types of graduated pipette (Fig. 3.45):

● A pipette with graduations to the tip (A). The total volume that can be measured is contained between the 0 mark and the tip.

● A pipette with graduations not extending to the tip (B). The total volume is contained between the 0 mark and the last mark before the tip (this type is re- commended for quantitative chemical tests).

Various volumes can be measured using graduated pipettes. For example:

— a 10-ml pipette can be used to measure 8.5 ml;

— a 5-ml pipette can be used to measure 3.2 ml;

— a 1-ml pipette can be used to measure 0.6 ml.

Fig. 3.44 A graduated pipette

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Centrifugation for laboratory use

1. Principle

A body is rotated in a circular movement at speed. This creates a force that drives the body away from the centre of the circular movement (Fig. 3.35). To calculate the relative centrifugal force (rcf) for an individual centrifuge, measure the radius (r) of the rotor arm (in cm) and the number of revolu- tions per minute (rpm) and use the formula below: rcf = 1.118 x 10-6 x r x (rpm)2

For example, if the radius is 25 cm and the rpm is 1300 rev/min, the rcf is about 50g.

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Weighing: use of laboratory balances

Balances may be either electrically or manually operated. All types should be posi- tioned on a firm level bench away from vibrations, draughts and direct sunlight. 

The balance is used to weigh chemicals for production of reagents, and cleanliness is essential if accurate results are to be obtained: 

● Remove dust by blowing or using a soft brush. 

● Remove stains or chemicals using a soft brush. 

● Use a plastic weigh boat or filter-paper to weigh chemicals on the balance; never place chemicals directly on to the pan.

Important: If water has been used to clean the balance, make sure that it is thoroughly dry before weighing. Always set the balance to zero before weighing. Check the accuracy of the balance regularly according to the manufacturer’s recommen- dations. Handle loose weights with forceps. 

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Use of a microscope in laboratory

The microscope is an essential instrument for the diagnosis of disease. It is a preci- sion instrument and requires careful maintenance to prevent damage to the me- chanical and ocular parts and also to stop fungi from obscuring the lenses. 

1. Components of a microscope 

The various components of the microscope can be classified into four systems: 

— the support system 

— the magnification system 

— the illumination system 

— the adjustment system. 

Support system (Fig. 3.1) 

This consists of: 

— the foot (1) 

— the limb (2) 

— the revolving nosepiece (objective changer) (3) 

— the stage (4) 

— the mechanical stage (5), which gives a slow con- trolled movement to the object slide. 

Magnification system (Fig. 3.2) 

This consists of a system of lenses. The lenses of the microscope are mounted in two groups, one at each end of the long tube — the body tube. 

● The first group of lenses is at the bottom of the tube, just above the preparation under examination (the object), and is called the objective. 

● The second group of lenses is at the top of the tube and is called the eyepiece. 

Objectives

Magnification

The magnifying power of each objective is shown by a figure engraved on the sleeve of the lens (Fig. 3.3):

— the x 10 objective magnifies 10 times;

— the x 40 objective magnifies 40 times;

— the x 100 objective magnifies 100 times.

Fig. 3.1 Components of the support system of a microscope
1: foot; 2: limb; 3: revolving nosepiece; 4: stage;
5: mechanical stage.

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Equipments for laboratory use

The following is a list of the apparatus needed to equip a laboratory capable of carrying out all the examinations described in this manual. Such a laboratory would usually be located in a small rural hospital (district level) which might have be- tween 60 and 100 beds.

1. Essential laboratory instruments

Microscopes

The laboratory should be equipped with two microscopes.

● One microscope is for use in haematology. It should have an inclined binocular tube, a mechanical stage, three objectives (x 10, x 40, x 100), two eyepieces (x 5,x 10), a condenser and an electric lamp that can be connected to the mains electricity supply or a battery.

● The second microscope is for use in other laboratory procedures (parasitology, urine analysis, bacteriology, etc.) and should have an inclined binocular tube and accessories as listed above.

At the health centre level one binocular microscope is sufficient.

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Water for laboratory use

The medical laboratory needs an adequate water supply for its work. It requires: 

— clean water 

— distilled water 

— demineralized water (if possible) 

— buffered water (if possible). 

1. Clean water 

To check whether the water supply is clean, fill a bottle with water and let it stand for 3 hours. Examine the bottom of the bottle. If there is a deposit, the water needs to be filtered. 

Filtering

Using a porous unglazed porcelain or sintered glass filter

This type of filter can be attached to a tap. Alternatively, it can be kept immersed in a container of the water to be filtered (Fig.2.28).

Important: Filters of this type must be dismantled once a month and washed in boiling filtered water.

Fig. 2.28 Filtering water using  a porous unglazed porcelain or sintered glass  filter

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Plumbing: simple procedures in laboratory

A fault in the plumbing of the laboratory (a dripping tap, a blocked sink, etc.) can hamper laboratory work considerably. Some simple remedies are described below, in case a plumber is not readily available.

Fig. 2.15 Tools and materials for plumbing repairs

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Electricity in laboratory

A reliable energy supply should be available to ensure continuity of the work in a laboratory. The energy can be provided from the following sources:

— mains electricity supply

— generators

— solar energy supply system.

Remote laboratories often have problems in ensuring a continuous supply of elec- trical power and may need to generate electricity by using a local generator or a solar energy supply system.

1. Sources of electricity

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Plan of a peripheral medical laboratory

1. A one-room laboratory

Figure 2.1 sets out the possible arrangement of a peripheral medical laboratory attached to a health centre. It shows a laboratory suitable for carrying out some or all of the techniques described in the manual. The plan is limited to one room, since often this is all the space that is available for the laboratory. The room should measure at least 5 m ¥6m.

Figure 2.2 indicates another possible arrangement of a peripheral laboratory. It can obviously be modified to suit different circumstances.

Fig. 2.1 Plan for a one-room laboratory

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