HAEMOSTASIS
antiphospholipid antibodies. In some conditions, the frequency of the association is sufficiently strong to be convincing. In others, however, a genuine association is difficult to establish because of the low frequency of the supposedly associated conditions, the relatively high prevalence of antiphospholipid antibodies in normal subjects, or in patients with other non-thrombotic disease, and the inadequacy of laboratory tests for antiphospholipid antibodies. The poor quality of evidence in some areas can lead to confusion and may have potentially clinically significant consequences if antiphospholipid syndrome is inappropriately diagnosed and treated. The problems of correctly diagnosing
antiphospholipid syndrome were expanded upon by Professor Vittorio Pengo, (Padova, Italy) in his presentation Antiphospholipid Syndrome: Critical Overview of Current Guidelines. In the previous presentation, Prof. Greaves discussed the problems associated with correctly diagnosing antiphospholipid syndrome, with a focus on the clinical findings. In his presentation, Prof. Pengo illustrated how problems can be compounded by the laboratory findings and their interpretation. Laboratory diagnosis of antiphospholipid syndrome is based on finding a positive result in at least one test to detect the presence of antiphospholipid antibodies. These tests include lupus anticoagulant, anticardiolipin antibodies and anti-β2- glycoprotein 1 antibodies. All of these investigations are poorly standardised as illustrated by UK NEQAS data. There is a lack of appropriate reference and control materials, difficulty in assigning normal ranges or cut-off values, use of different reporting units, and general lack of assay precision. Antiphospholipid antibodies are a very heterogeneous group of proteins and different antibody types have different thrombogenicity. Rather than considering antibodies and test results in isolation, it is now thought that an approach that
considers the profile of test results in the clinical context is most useful in establishing a link with thrombosis and consequent diagnosis of the antiphospholipid syndrome. Thus, for example, the isolated finding of anticardiolipin antibodies in a patient with a thrombotic event should not usually lead to a diagnosis of antiphospholipid syndrome. The risk of thrombosis or pregnancy loss is increased if more than one test is positive, and the risk is significantly increased if all three are positive. Prof. Pengo drew similar conclusions to Prof. Greaves in that, before a diagnosis of antiphospholipid syndrome is made, careful consideration must be given to the profile of laboratory results, the presence of associated autoimmune disease and the presence of other risk factors for thrombosis or pregnancy loss.
Point-of-care testing Dr Alastair Nimmo (Edinburgh) reviewed Haemostasis Testing in the Operating Theatre. Anaesthetists are often faced with the challenge of managing bleeding in the absence of meaningful information on the nature and severity of any coagulation disturbance. In cases of significant trauma, massive blood loss or major surgery, haemostasis can be extremely dynamic, with significant changes occurring in the space of a few minutes. Consequently, in these situations, standard laboratory tests of haemostasis are of limited use, as the results may bear little relationship to the current haemostatic state of the patient, due to the time that has elapsed between the sample being taken and the results being available. Point-of-care (POC) testing in the operating theatre using thromboelastography or thromboelastometry permits rapid identification of thrombocytopenia, reduced levels of pro-coagulant clotting factors, hypofibrinogenaemia, fibrinolysis and the effect of heparin. The consequent
The risk of thrombosis or pregnancy loss is increased if more than one test is positive, and the risk is significantly increased if all three are positive.
ability to give rapid and targeted therapy avoids the unnecessary use of blood products and has been shown to improve patient outcomes. Optimal and safe use of such a strategy depends upon having well-defined standard operating procedures and suitably trained and experienced individuals, available at all times, who can perform the tests and interpret the results. The devices used must be subject to appropriate quality control checks and should be included in external quality assessment programmes, if available. In addition to the information provided by thromboelastography or thromboelastometry, POC whole blood platelet function analysers can give information on the presence of antiplatelet drugs, the effect of which is increasingly seen.
Monitoring or measuring? The next presentation took the form of a debate, ‘Access to Laboratory Monitoring is Necessary for the Safe Use of the New
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