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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