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. The specimen may come from any part of the body and include blood, tissue or body fluids. Incorrect specimen selection or technique can be life threatening to patients (Chernecky and Berger [32], Pagana and Pagana [177]). Specimens should only be taken when there are clinical indications – for example, signs of infection. Signs of infection, such as fever, should trigger a careful clinical assessment to ensure that unnecessary tests are avoided and the most useful laboratory samples are obtained to identify therapeutic options (Pagana and Pagana [177]).

The production of high‐quality, accurate results that are clinically useful is very much dependent upon the quality of the specimen collection (Higgins [84], Pagana and Pagana [177]). Additionally, 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. The timing of specimen collection is especially important during the acute phase of viral infections. Many viral illnesses have a prodromal phase where multiplication and shedding of the virus are usually at their peak and when the patient is most infectious. This is often before the onset of clinical illness and has often ceased by about day 5 from the onset of symptoms. At this stage, the patient's immune response against the virus will already have been been mounted and may therefore affect organism isolation (Chernecky and Berger [32], Keogh [114], Pagana and Pagana [177]).

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 (Keogh [114], Pagana and Pagana [177]). Therefore, a clean technique must be used to avoid inadvertent contamination of the site of the sample or the specimen itself. Specimens should also be collected in sterile containers with close‐fitting lids.

A variety of medical devices are used before, during and after diagnostic tests. For blood, body fluids and tissue specimens, various blood bottles, sterile pots, swabs and other receptacles are required (following local policy and guidelines) (Figures 13.1, 13.2, 13.3, 13.4). It is essential that the specimen and its transport container are appropriate for the type of specimen or sample. Failure to use the correct collection method and equipment leads to inaccurate results and potentially incorrect or unnecessary treatments. Other medical devices, such as X‐ray machines or endoscopes, may be used to undertake a diagnostic test or procedure. It is essential to ensure practitioners are aware of local variation in types and manufacturers of medical devices and have been trained in their use prior to undertaking a diagnostic test or procedure.

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, body fluids, secretions or excretions of patients (Gould and Brooker [75]). In addition to considering personal protection, the person collecting the specimen should 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 [203], WHO [260]).

In relation to specimen collection, standard (universal) infection control precautions should include the following (RCN [203]):

Selection of personal protection equipment 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 a risk of blood, body fluid, secretions or excretions splashing into the eyes or face (RCN [203]).

The request form should include as much information as possible as this allows the laboratory or department conducting the diagnostic procedure or investigation to select the most appropriate equipment and/or media for examination (IBMS 2016). Request forms should include some or all of the following information, depending on the type of diagnostic test or procedure:

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.