Lupus anticoagulant in the blood.

Reference values (norm) of lupus anticoagulant in blood plasma are 0.8-1.2 conventional units.

Lupus anticoagulant is an IgG class Ig and is an antibody against negatively charged phospholipids. It received its name due to the fact that it affects phospholipid-dependent coagulation tests and was first identified in patients with systemic lupus erythematosus. The presence of lupus anticoagulant in patients can be suspected by unexplained prolongation of APTT, recalcification time and, to a lesser extent, prothrombin time with normal results of all other coagulogram parameters. Lupus anticoagulant is usually detected by prolongation of APTT in patients, while they do not have pronounced manifestations of bleeding, and thrombosis develops in 30%, that is, a paradoxical combination is observed - prolongation of APTT and a tendency to thrombosis. The mechanism of thrombosis development in patients with lupus anticoagulant is currently not precisely established, but it is known that antiphospholipid antibodies reduce prostacyclin production by endothelial cells due to inhibition of phospholipase A ₂ and protein S and, thus, create prerequisites for thrombus formation. Currently, lupus anticoagulant is considered a significant risk factor in patients with unexplained thromboses and is often detected in various forms of pathology, especially in systemic, autoimmune diseases, antiphospholipid syndrome, in patients with HIV infection (20-50%), in women with habitual miscarriages and intrauterine fetal death, in patients with complications of drug therapy. Thromboembolism develops in approximately 25-30% of patients with lupus anticoagulant. In systemic lupus erythematosus, lupus anticoagulant is detected in 34-44% of patients, and in 32% of patients receiving phenothiazine for a long time. False-positive results in syphilis testing are often observed in patients with lupus anticoagulant in the blood. The frequency of detection of lupus anticoagulant correlates better with the risk of thrombosis than the frequency of detection of anticardiolipin antibodies.

Detection of lupus anticoagulant is based on prolongation of phospholipid-dependent coagulation reactions. However, due to the lack of standardization of these studies and the ambiguous results, in 1990 the lupus anticoagulant subcommittee of the International Society on Thrombosis and Haemostasis recommended guidelines for detection of lupus anticoagulant.

• Stage I includes screening studies based on prolongation of phospholipid-dependent coagulation tests. For this purpose, such tests as APTT with minimal phospholipid content are used, which is much more sensitive to the presence of lupus anticoagulant than the usual APTT; prothrombin time with diluted tissue thromboplastin; diluted Russell viper venom time; kaolin time. It is impossible to judge the presence of lupus anticoagulant based on prolongation of screening tests, since it can be a result of circulation of other anticoagulants, such as specific inhibitors of coagulation factors, FDP, paraproteins, as well as deficiency of blood coagulation factors or the presence of heparin or warfarin in the plasma.
• Stage II - correction test, implies clarification of the genesis of screening test prolongation. For this purpose, the plasma under study is mixed with normal plasma. Shortening of the clotting time indicates a deficiency of clotting factors. If the time is not corrected, and in some cases even lengthens, this indicates an inhibitory nature of screening test prolongation.
• Stage III is a confirmatory test, the purpose of which is to determine the nature of the inhibitor (specific or non-specific). If the time is shortened when adding excess phospholipids to the plasma being tested, this is evidence of the presence of a lupus anticoagulant; if not, specific inhibitors of blood coagulation factors are present in the plasma.

If the first screening test for lupus anticoagulant is negative, this does not mean that it is absent. Only if two screening tests are negative can one judge that there is no lupus anticoagulant in the blood plasma.

When assessing the results of the study on lupus anticoagulant by APTT with a minimum content of phospholipids, it is necessary to focus on the following data: if the result of the study on lupus anticoagulant is 1.2-1.5 conventional units, then the lupus anticoagulant is present in small quantities, and its activity is low; 1.5-2 conventional units - lupus anticoagulant is detected in moderate quantities, and the probability of thrombosis development increases significantly; more than 2.0 conventional units - lupus anticoagulant is present in large quantities and the probability of thrombosis development is very high.

Determination of lupus anticoagulant and anticardiolipin antibodies is indicated in all patients with signs of hypercoagulability, even if their APTT is not prolonged.

When prescribing a test for lupus anticoagulant, the patient must stop taking heparin 2 days before, and oral anticoagulants 2 weeks before blood sampling, since the presence of these drugs in the blood can give false positive results.

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