The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [402]
Evidence-based approaches
Rationale
Successful laboratory diagnosis depends upon the collection of specimens at the appropriate time, using the correct technique and equipment, and transporting them to the designated laboratory safely without delay (Box 11.1). For this to be achieved, it is essential that there is good liaison between medical, nursing, portering and laboratory staff (Mims 2004).
Box 11.1 Good practice in specimen collection
Appropriate to the patient’s clinical presentation.
Collected at the right time.
Collected in a way that minimizes the risk of contamination.
Collected in a manner that minimizes the health and safety risk to all staff handling the sample.
Collected using the correct technique, correct equipment and in the correct container.
Documented clearly, informatively and accurately on the request forms.
Stored/transported appropriately.
(Higgins 2008)
The clinical microbiology laboratory plays a fundamental role in the diagnosis of infection and an increasingly important role in reducing new antibiotic resistance (Woodford et al. 2004). A team approach helps to facilitate more effective infection prevention and control strategies. Close communication between the medical, nursing and laboratory teams is particularly important when unusual infections are suspected or if the patient is immunosuppressed as the infection may be caused by an unusual organism whose identification requires special processing techniques (Thomson 2002).
Indications
Collecting a specimen is often the first crucial step in determining diagnosis and subsequent mode of treatment for patients with suspected infections or to aid in the diagnosis of specific conditions. In other aspects the collection may help determine variation from normal values such as blood sampling or endoscopic findings.
Principles of care
Nursing staff are in a unique position and play a key role within the microbiological process because they often identify the need for microbiological investigations, initiate the collection of specimens and assume responsibility for timely and safe transportation to the laboratory (Higgins 2007). Specimen collection is often the first crucial step in investigations that define the nature of the disease, determine a diagnosis and therefore the mode of treatment.
Methods of investigations
Initial examination
Specimens will be initially examined for clinical variables such as odour, appearance, consistency and turbidity. Foul-smelling, purulent material is suggestive of anaerobic bacteria, cloudy cerebrospinal fluid (CSF) or urine suggests the presence of neutrophils, stool may contain blood or mucus and parasites such as roundworms or tapeworms which are visible to the naked eye (Gould and Brooker 2008).
Direct microscopy
The majority of specimens will then undergo direct microscopic investigation which is valuable as an early indication of the causative organism. High magnification is required to visualize viruses, which are then identified according to their characteristic shapes (Gould and Brooker 2008). Certain parasitic protozoa, such as malaria, are identified by direct microscopy which necessitates the specimen being delivered to the laboratory as quickly as possible whilst the protozoa are mobile and therefore visible (Higgins 2007). In combination with clinical presentations, this may be enough to initiate or change targeted treatments until a more definitive diagnosis is reached (Weston 2008).
Gram staining
Gram staining is a process by which staining substances are added to a sample to differentiate the type of organisms present. Cells with differing properties stain differently in relation to the structure of their cell wall (Mims 2004).
Gram staining allows for the differentiation between Gram-positive bacteria (e.g. Staphylococcus aureus), which will stain purple, and Gram-negative bacteria (e.g. Escherichia coli), which will stain pink when viewed under the microscope. This can be used to guide the choice of antimicrobial therapy until other investigation methods can provide a definitive