General rule for
specimen collection
1.
The quantity of
specimen must be adequate.
2.
The sample
should be collected from the appropriate region of the body.
3.
Contamination of
the specimen must be avoided by using only sterile equipment and aseptic
conditions.
4.
Always collect
specimens prior to administration of antimicrobial drugs.
5.
Specimens may be
infectious, so proper precaution like wear gloves, gowns, masks and goggles,
whenever necessary.
6.
Specimen
containers labeled with information about patient name, code number etc. and
the specimen source, date and time of collection.
Collection
Specimens
are collected by several methods using septic techniques. Aseptic techniques
refer to specific procedures used to prevent unwanted microorganisms from
contaminating the clinical specimens.
Skin,
Nails and Hair
Skin,
nails and hair should be collected into folded squares of black paper. The use
of paper permits the specimen to dry out, which helps to reduce bacterial
contamination. Wood's light will be used to select infected scalp hairs for
laboratory investigation. Hairs give the green flourescence which is a feature
of some forms of dermatophyte scalp infection. Hairs should be plucked from the
scalp with forceps. Nail specimens should be taken from any discoloured, dystrophic
or brittle parts of nail
Mucous
Membrane
Although
scrapings from oral lesions are better than swabs for diagnosis of oral
infections. Swabs are more frequently used, mainly because they are more
convenient for transporting material to the laboratory. Swabs should be either
be moistened with sterile water or saline prior to taking the sample or sent to
the laboratory in transport medium.
Anterior
nares or Throat
The
most common method used to collect specimens from the anterior nares or throat
is the sterile swab. Commercially manufactured swab contain a transport medium
designed to preserve a variety of microorganisms and to prevent multiplication
of rapidly growing members of the population.
Ear
Scrapings
of material from the ear canal are mostly preferred, although swabs can also be
used.
Sputum
Sputum
is the most common specimen collected in suspected cases of lower respiratory
tract infections. Sputum is the mucous secretion expectorated from the lungs,
bronchi and trachea through the mouth. Sputum is collected in specially
designed sputum cups.
Urine
Proper
collection of the specimen is the single most important step in a urine
culture.
Faeces
Stool
specimens are collected in clean sterile leak-proof containers
Blood
The
following rules are applied to collect blood specimens.
1.
Use strict aseptic techniques. Wear gloves.
2.
Apply a tourniquet and locate a fixed vein by touch. Release the tourniquet
while the skin is being prepared.
3.
Prepare the skin for venipuncture by cleansing it vigorously with
70
- 95% isopropyl alcohol. Using 2% tincture of iodine or 2% chlorhexidine, start
at the venipuncture site and cleanse the skin in concentric circles of
increasing diameter. Allow the aseptic preparation to dry for at least 30
seconds. Do not touch the skin after it has been prepared.
Reapply
the tourniquet, perform venipuncture, and (adults) withdraw approximately 20 ml
of blood.
5.
Add the blood to labelled aerobic and anaerobic blood culture bottles.
6.
Take specimens to the laboratory promptly, or place them in an incubator at
37°C.
Cerebrospinal
Fluid
As
soon as infection of the central nervous system is suspected, cerebrospinal
fluid is obtained for analysis. To obtain cerebrospinal fluid, perform lumbar
puncture with strict aseptic techniques, taking care not to risk compression of
the medulla by too rapid withdrawal of fluid when the intracranial pressure is
markedly elevated. Cerebrospinal fluid is usually collected in three or four
portions or 2-5ml each, in sterile tubes.
Pus
and Wound secretions
For
surface wounds collect sample material with smear swabs and transport in
preservative transport mediums. Such material are analysed for aerobic
bacteria. For deep and closed wounds, liquid material (e.g. pus) should be
sampled if possible, with a syringe. Use special transport medium for
anaerobes.
Eye
swabs
The
swab is gently rubbed over the conjunctiva in the lower conjunctival sac.
Conjuctival swabs should be inoculated onto an agar plate at the patient's
bedside and then sent to the laboratory.
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