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Collection and Handling of Blood


Acknowledgement

The author wishes to acknowledge the contribution of previous authors of this chapter – the late Corrine Jury, Yutaka Nagai and the late Noriyuki Tatsumi – and of Gareth Ellis, who reviewed the content of this chapter.

Following an informed decision to analyse a blood sample, a specimen must be safely and correctly procured. It is essential to be aware that variation in this pre-analytical phase of the testing process can lead to errors in the analytical phase (see Box 1-1 ).

Box 1-1
Causes of misleading results related to specimen collection

Pre-collection

  • Urination within 30 min; food or water intake within 2 h

  • Smoking

  • Physical activity (including fast walking) within 20 min

  • Stress

  • Drugs or dietary supplement administration within 8 h

During collection

  • Different times (diurnal variance)

  • Posture: lying, standing or sitting

  • Haemoconcentration from prolonged tourniquet pressure

  • Excessive negative pressure when drawing blood into syringe

  • Incorrect type of tube

  • Capillary versus venous blood

Handling of specimen

  • Insufficient or excess anticoagulant

  • Inadequate mixing of blood with anticoagulant

  • Error in patient and/or specimen identification

  • Inadequate specimen storage conditions

  • Delay in transit to laboratory

Venous blood is used for most examinations. Capillary blood samples may be satisfactory for some purposes but in general the use of capillary blood should be restricted to children and to some point-of-care screening tests.

Biohazard precautions

Laboratory policies must be in place to ensure that staff who collect blood samples and transfer them to the laboratory minimise the risk of infection from various pathogens during all aspects of specimen handling (see Chapter 24 ). Additional precautions should be taken when handling high-risk specimens (e.g. those from patients suspected of having a viral haemorrhagic fever). In this circumstance, the collection policy should stipulate the use of personal protective equipment, such as disposable gloves, body apron and protective eyewear. Care must be taken to prevent injuries, especially when handling and disposing of needles and lancets. Recommendations for standardising blood collection have been published. ,

Procurement of venous blood

Equipment

It is important to assemble a tray or prepare a workspace that has all the requirements for blood collection ( Box 1-2 ). The selection of needle diameter is a compromise between achieving adequate flow with minimal turbulence and minimising patient discomfort. A 19-gauge (19G) or 21G *

* The International Organisation for Standardisation has established a standard (ISO 7864), which relates the following diameters for the different gauges: 19G = 1.1 mm; 21G = 0.8 mm; 23G = 0.6 mm.

needle is suitable for most adults. A 23G needle is often selected for children. The shaft of the needle should be short (about 15 mm). It may be helpful to collect the blood by means of a winged needle (often referred to as a ‘butterfly’ ) connected to a length of plastic tubing that can be attached to the nozzle of the syringe or to a needle for entering the cap of an evacuated container (see Specimen Containers ).

Box 1-2
Items to be included in a phlebotomy tray

  • Syringes and needles

  • Tourniquet

  • Specimen containers (tubes or evacuated tube system) – plain and with various anticoagulants

  • Request form

  • 70% isopropanol swabs or 0.5% chlorhexidine

  • Sterile gauze swabs

  • Adhesive dressings

  • Self-sealing plastic bags with a separate compartment for the request form

  • Rack to hold specimens upright during process of filling (except when an evacuated tube system is used)

  • Puncture-resistant disposal container

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