Point of care testing

Point of care testing, in this context, means using simple laboratory equipment in operating theatres. Because laboratory coagulation tests take at least 20 minutes to complete (and usually longer, taking sample transport into account), there has been a move to use Near Patient Testing with a number of different devices.

• Whole blood clotting time - ACT- this is used in Cardiac Theatres to monitor the heparin effect
• PT and APTT devices - e.g. Coaguchek - these are designed mainly for testing patients on oral anticoagulants
• Thromboelastogram - The TEG is used in Liver and Cardiac units. It gives information relating to platelet function, clot strength and fibrinolysis within about 15 minutes
• In-vitro Platelet Function (PFA-100) is an in-vitro bleeding time test whose current role is determining mild VWD and platelet defects.

Point of Care Testing Guidelines

The following Point of Care Testing (POCT) guidelines provide a framework for the development of a POCT service including advice in relation to identifying need, developing a business case, clinical governance, accountability, development of standard operating procedures, training and quality assurance

Management and Use of In Vitro Diagnostic Medical Device (IVD) Point of Care Test Devices, Medical Devices Agency, download at http://www.dhsspsni.gov.uk/hea-db(ni)2002-03.pdf

Guidelines for point of care testing: haematology, BCSH General Haematology Task Force, download at http://www.bcshguidelines.com/pdf/POCT_guidelines_310707.pdf

Guidelines on point-of-care testing, The Royal College of Pathologists, download at www.rcpath.org/resources/pdf/point-of-care-testing

Point-of-Care Testing, Guidance on the involvement of the clinical laboratory, Institute of Biomedical Science, download at www.ibms.org/pdf/point_of_care_testing.pdf

Thromboelastography

Thromboelastography is a near patient test to analyze the visco- elastic properties of whole blood and produce graphic displays, easily interpreted in operating theatres. These results can demonstrate primary fibrinolysis, secondary fibrinolysis, failure to reverse protamine and whether blood products are required. Easy to follow protocols can be used correlating thromboelastography values and traces with clinical circumstances, and suggesting appropriate corrective actions. The patient’s progress can be monitored with successive tests. Thromboelastography is in use in numerous cardiac and transplant surgery operating theatres and studies have shown that it is a significantly better predictor of postoperative haemorrhage and the need for re-operation than the conventional coagulation profile.

Two instruments are currently commercially available, the TEG® (Haemoscope Corporation IL. USA) distributed by Medicell in the UK, and the newer Rotem® distributed in the UK by Diagnostica Stago. Both are designed to analyze the viscoelastic changes occurring during clot formation, including evaluation of clot initiation, formation and stabilization using either whole blood or plasma. Current convention dictates that the term thromboelastography refers to measurements made using the TEG® device, and thromboelastometry refers to measurements made using the Rotem® device. Both devices produce a graphical display of clot development and lysis.

TEG®
In conventional thromboelastography (TEG®), a sample of whole blood is placed in a cuvette warmed to 370C. The cuvette rotates back and forth through an angle of 4045’ with a cycle time of 6 per minute including a one second rest period at the end of each excursion. A sensor connected to a torsion wire is lowered into the cuvette, and as the clot develops, strands of fibrin become attached between the internal surface of the cuvette and the sensor thus influencing the degree of rotation of the cuvette. Clot development and stabilization, as defined by the rotation of the pin, is converted by a mechanical-electric transducer to an electrical signal. This is then recorded and displayed on a computer.

Rotem®
The Rotem® uses a modification of this approach. A sample of citrated whole blood is placed in the pre-warmed (370C) the sample is activated with tissue factor or a contact factor activator. The cuvette is placed into a piston that rotates through a 4.750 arc through the blood whilst the cuvette remains stationary. The subsequent clot formation influences the rotation of the suspended piston, this change is identified by an optical detector, and the information transmitted to a computer for analysis

Example documentation relating to the Rotem®:
Guide to Rotem® Analysis (pdf 326KB)

Examples of transfusion protocols based on thromboelastography:
Cardiac Recovery Unit Blood Components Transfusion Protocol (pdf 20KB)
Adult ITU Blood Component Treatment Algorithm (pdf 25KB)