Background
- it is one of the the laboratory tests needed to make the diagnosis of antiphospholipid syndrome (APS) (the other is clinical: one cerebrovascular accident or pregnancy complication, i.e. intra-uterine death and spontaneous abortion).
- other laboratory tests for APS are: ELISA for anti cardiolipin and anti beta-2 glycoprotein.
- paradoxically, the presence of LAC gives increase of the coagulation time.
How
- there are several options to screen in the routine lab, for example APTT and PT.
- the LAC tests itself consist of a series of test: screening, mix and confirmation.
Screening and confirmation
- for screening test it is advised to perform at least 2 tests which asses the intrinsic and common pathways, for example APTT (with lupus sensitive reagens, in contradictory to the routine APTT, and dRVVT).
- some screening tests are coupled with confirmation test (using activator with higher concentration of phospholipids). Some other deliver the kit separately. Coupled tests should be interpreted together.
- when the coagulation time is corrected with the confirmation tests (higher concentration of phospholipids), than lupus anticoagulans is present.
Mixing
- the last test, which is not always done is the mixed test, 1 part of patient's plasma is mixed with 1 part of mixed plasma from 30 patients with normal clotting time (50% female, <50 years old). Then, added the factor that start the clotting time.
- when the time is not corrected there is lupus (or specific factor inhibitor) but if the time is corrected the cause is factor deficency.
Interpretation
- all calculation is performed related to the pooled plasma.
- the test is concluded by either positive or negative.
Other considerations
- the test should be repeated again with at least 12 weeks difference. This to prevent intermittent positivity due to for example infection.
- it is one of the the laboratory tests needed to make the diagnosis of antiphospholipid syndrome (APS) (the other is clinical: one cerebrovascular accident or pregnancy complication, i.e. intra-uterine death and spontaneous abortion).
- other laboratory tests for APS are: ELISA for anti cardiolipin and anti beta-2 glycoprotein.
- paradoxically, the presence of LAC gives increase of the coagulation time.
How
- there are several options to screen in the routine lab, for example APTT and PT.
- the LAC tests itself consist of a series of test: screening, mix and confirmation.
Screening and confirmation
- for screening test it is advised to perform at least 2 tests which asses the intrinsic and common pathways, for example APTT (with lupus sensitive reagens, in contradictory to the routine APTT, and dRVVT).
- some screening tests are coupled with confirmation test (using activator with higher concentration of phospholipids). Some other deliver the kit separately. Coupled tests should be interpreted together.
- when the coagulation time is corrected with the confirmation tests (higher concentration of phospholipids), than lupus anticoagulans is present.
Mixing
- the last test, which is not always done is the mixed test, 1 part of patient's plasma is mixed with 1 part of mixed plasma from 30 patients with normal clotting time (50% female, <50 years old). Then, added the factor that start the clotting time.
- when the time is not corrected there is lupus (or specific factor inhibitor) but if the time is corrected the cause is factor deficency.
Interpretation
- all calculation is performed related to the pooled plasma.
- the test is concluded by either positive or negative.
Other considerations
- the test should be repeated again with at least 12 weeks difference. This to prevent intermittent positivity due to for example infection.
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