Chapter 13: Diagnostic tests
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Source: Adapted from Gould and Brooker ([75]), Higgins ([84]), Pagana and Pagana ([177]).
Post‐procedural considerations
Handling specimens
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 [94], RCN [203], WHO [260]) (see Chapter c04: Infection prevention and control). Standard precautions must be in place at all times when handling any body fluids or specimens irrespective of infectious status (Pagana and Pagana [177]).
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 particular 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 secure lid (HSE [94], WHO [260]).
Clinical waste
It is essential that all clinical waste is disposed of appropriately. This ensures that healthcare activities do not go on to pose further infection risks and that waste is securely managed. There are various regulatory regimes (e.g. concerning environment and waste, controlled drugs, infection control, health and safety, and transport) that pertain to the destruction of healthcare waste. Specialist disposal of cytotoxic and radioactive waste must also be considered. Due to variations in product availability and local waste arrangements, it is important to follow local policy and guidelines (DH [48]) (see Chapter c04: Infection prevention and control).
Documentation
Labelling specimens
Incorrectly labelled and unlabelled specimens will be discarded (HSE [94], IBMS 2016). Samples should include the following information:
- patient's name, date of birth, ward and/or department
- hospital number
- date and time of specimen collection
- type and site of specimen: this should specify the anatomical site, such as ‘abdominal wound’, as this allows the laboratory to differentiate the target and non‐target pathogens and assess the significance of the results based upon the flora normally associated with that site (Keogh [114], Pagana and Pagana [177]).
Transporting specimens
An awareness of the type of specimen or organism being investigated gives the healthcare professional an insight into the correct storage and transportation methods. For example, most micro‐organisms are extremely susceptible to environmental fluctuations, such as in pH, temperature, ultraviolet rays and oxidizing agents (Table 13.1) (Gould and Brooker [75]). Incorrect or prolonged storage or transportation may result in the organism not surviving before cultures can be made. Delays in transporting a specimen to the laboratory can compromise the specimen's integrity, leading to false‐negative or false‐positive results or a misdiagnosis because the sample is no longer representative of the disease process (Higgins [84], Pagana and Pagana [177]).
Table 13.1 Types of organism
| Organism | Definition |
|---|---|
| Aerobic | Aerobic bacteria only grow in the presence of oxygen. |
| Anaerobic | Anaerobic bacteria prefer an atmosphere of reduced oxygen, such as deep in wound bed tissue, and facultative anaerobes can grow in either the presence or absence of oxygen. |
| Bacteria | Bacteria are unicellular organisms that multiply and die very rapidly, especially once they have been removed from their optimum environment. |
| Virus | Viruses are intracellular parasites that hijack the genetic material of the host cell and are therefore unable to multiply outside living cells. |
The sooner a specimen arrives in the laboratory, the greater the chance of organisms or disease being identified. Some pathogens do not survive for very long once they have left the host, while normal body flora within the sample may proliferate and overgrow, inhibiting or killing the pathogen (Weston [255]).
If delays are anticipated, samples need to be stored appropriately, depending on the nature of the specimen, until they can be processed. This could be in an ambient temperature storage unit, specimen fridge or freezer (HSE [94], WHO [260]). For example, blood cultures need to be incubated at 37°C, whereas swabs must be either refrigerated or kept at ambient temperature, depending on the site from which they were taken. Other specimens, such as tissue, may need to be stored in preservatives such as formaldehyde solution (WHO [260]).
Equipment used for transportation
Where a specimen is obtained within a healthcare setting, it should be transported either in a deep‐sided tray that is not used for any other purpose and is disinfected after each use (HSE [94], WHO [260]) or in a robust, leak‐proof container that conforms to the regulation Biological Substances, Category B: UN3373 (HSE [95], WHO [260]). Specimens that need to be moved outside the hospital or clinic must be transported using a triple‐packaging system (HSE [95], WHO [260]). 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 [95], WHO [260]). 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 [94], WHO [260]).
