Chapter 20: Diagnostic investigations
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Pre‐procedural considerations
Equipment
There is a variety of equipment/tools designed for the collection of specimens such as blood bottles, specimen pots and other receptacles (Figure 20.1 and Figure 20.2). It is essential that the specimen and its transport container are appropriate for the type of specimen or sample. Failure to utilize the correct collection method leads to inaccurate results so it is vital that an adequate quantity of material is obtained to allow complete examination.
Figure 20.1 Blood bottles.
Figure 20.2 Specimen pots.
Equipment used for transportation
Within healthcare institutions, specimens should be transported in deep‐sided trays that are not used for any other purpose and are disinfected weekly and whenever contaminated (HSE [68]), or robust, leak‐proof containers that conform to ‘Biological Substances, Category B – UN3373’ regulations (HSE [69]). Specimens that need to be moved outside the hospital must be transported using a triple‐packaging system dependent on the infectious status of the sample (HSE [69], WHO [171]). This consists of a watertight, leak‐proof, absorbent primary container, a durable, watertight, leak‐proof secondary container and an outer container that complies with ‘Biological Substances, Category B – UN 3373’ standards (HSE [69]). A box for transportation is essential and should carry a warning label for hazardous material. It must be made of smooth impervious material, such as plastic or metal, which will retain liquid and can be easily disinfected and cleaned in the event of a spillage (HSE [68], WHO [171]).
Handling specimens
Specimens should be obtained using safe techniques and practices and practitioners should be aware of the potential physical and infection hazards associated with the collection of diagnostic specimens within the healthcare environment. Standard (universal) infection control precautions should be adopted by healthcare workers who have direct contact or exposure to the blood, bodily fluids, secretions and excretions of patients (Gould and Brooker [57]). In addition to personal protection, the person collecting the specimen should also be mindful of the collective health and safety of other people involved in the handling of samples. Every health authority must ensure that medical, nursing, phlebotomy, portering and any other staff involved in handling specimens are trained to do so (RCN [132], WHO [171]).
In relation to specimen collection, standard (universal) infection control precautions should include the following (RCN [132]):
- hand hygiene
- the use of personal protection equipment (PPE)
- safe sharps management
- safe handling, storage and transportation of specimens
- waste management
- clean environment management
- personal and collective management of exposure to body fluids and blood.
Selection of PPE should be based upon an assessment of risk of exposure to body fluids. As minimum precautions, gloves and aprons should be worn when handling all body fluids. Protective face wear (e.g. goggles, masks and visors) should be worn during any procedure where there is risk of blood, body fluid, secretions or excretions splashing into the eyes or face (RCN [132]).
Specimens should be placed in a double, self‐sealing bag with one compartment containing the specimen and the other containing the request form. The specimen container used should be appropriate for the purpose and the lid should be securely closed immediately to avoid spillage and contamination. The specimen should not be overfilled and not be externally contaminated by the contents. Any accidental spillages must be cleaned up immediately by staff wearing appropriate protective equipment (HSE [68], RCN [132], WHO [171]).
If a specimen is suspected or known to present an infectious hazard, particularly Hazard Group 3 pathogens (such as hepatitis B or C virus, human immunodeficiency virus [HIV], Mycobacterium tuberculosis), this must be clearly indicated with a ‘danger of infection’ label on the specimen and the request form to enable those handling the specimen to take appropriate precautions (HSE [68], WHO [171]).
Specimens from patients who have recently been treated with toxic therapy such as gene therapy, cytotoxic drugs, radioactivity or active metabolites need to be handled with caution. Local guidelines on the labelling, bagging and transportation of such samples to the laboratory should be followed. For example, in the case of gene therapy, the specimen must be labelled with a ‘biohazard’ label, double bagged and transported to the laboratory in a secure box with a fastenable lid (HSE [68], WHO [171]).
Selecting specimens
Selecting a specimen that is representative of the disease process is critical to the ability of the laboratory to provide information that is accurate, significant and clinically relevant. Incorrect specimen selection or technique can be life threatening to patients (Wegerhoff [168]). Specimens should only be taken when indicated.
Assessment and recording tools
Request forms
The form should include as much information as possible as this allows the laboratory or department conducting the investigation to select the most appropriate equipment and/or media examination (NHS Pathology [101]).
Request forms should include the following information:
- patient's name, date of birth, ward and/or department
- hospital number
- investigation required so as to avoid indiscriminate specimen analysis which wastes time and money
- date and time of specimen collection
- type and site of specimen; this should specify the actual anatomical site
- diagnosis and relevant clinical information which can help in the interpretation of a sample (Higgins [65])
- relevant signs and symptoms
- relevant history, for example recent foreign travel
- present or recent antimicrobial therapy
- whether the patient is immunocompromised as these patients are highly susceptible to opportunistic infections and non‐pathogenic organisms (Weston [169])
- consultant's name
- name and contact details of the doctor requesting the investigation, as it may be necessary to telephone the result before the report is dispatched.
- labelled with ‘danger of infection’ if the specimen is high risk (HSE [68], WHO [171]).
Communication
For certain specimens that have specific collection techniques or require prompt processing, communication with the laboratory before the sample collection is essential. Providing specimen arrival time to the laboratory can improve efficiency of processing and accuracy of results. Where a diagnostic test is to be undertaken, it is essential that the patient is prepared appropriately with consideration of fasting times, the cessation of certain medications and post‐procedural care. A patient information leaflet explaining the test can be given to prepare the patient for pre‐ and post‐procedural care. Communication with the department where the test will be conducted is essential.
Collecting specimens
The production of high‐quality, accurate results which are clinically useful is very much dependent upon the quality of the specimen collection (Higgins [65], Wegerhoff [168]). The greater the quantity of material sent for laboratory examination, the greater the chance of isolating a causative organism. Specimens should be taken as soon as possible after the manifestation of clinical signs and symptoms.
Specimens are readily contaminated by poor technique, and analysis of such specimens could lead to adverse outcomes such as misdiagnosis, misleading results, extended length of stay, inappropriate therapy or potentially disastrous consequences for the patient (Wegerhoff [168]). Therefore, care must be taken to avoid inadvertent contamination of the site of the sample or the specimen itself.
