Other analyses
Lupus anticoagulans
Antibodies that prolong clotting tests but increase the risk of thrombosis; part of testing for antiphospholipid syndrome.
Everything about this testWhat it measures
Despite the name, lupus anticoagulant is not an anticoagulant and is not found only in the disease lupus. These are autoantibodies: antibodies that the body makes by mistake against proteins that bind to phospholipids (fat-like building blocks of cells). In the tube they prolong clotting tests, but in the body they actually increase the risk of thrombosis. The laboratory measures them with the dRVVT (dilute Russell's viper venom time): a screening test and a confirmation test with extra phospholipids. If the screening time is prolonged and becomes shorter with extra phospholipids, lupus anticoagulant is present.
- Lupus anticoagulant: one of the three laboratory tests for antiphospholipid syndrome (APS)
- An explanation for an unexplained prolonged aPTT
- An increased risk of thrombosis or pregnancy complications if the antibodies are persistently present
Positive
A positive result means that lupus anticoagulant has been detected. That is not yet a diagnosis: according to the Dutch Society for Clinical Chemistry (NVKC) and the Dutch medical specialists' guideline (FMS), the test is repeated after at least 12 weeks, because lupus anticoagulant can also be present temporarily, for example during or after an infection. If the result is positive again and there has been a thrombosis or a pregnancy problem, such as repeated miscarriages, antiphospholipid syndrome may be present. Lupus anticoagulant is more common in people with the autoimmune disease lupus (SLE). According to the NVKC, a positive result without thrombosis and without pregnancy problems does not in principle lead to treatment.
Negative
A negative result means that no lupus anticoagulant was found with this test. That does not rule out antiphospholipid syndrome: the laboratory only uses the dRVVT, while international agreements also call for a second test based on the aPTT, and the syndrome can also show up as antibodies against cardiolipin or beta-2 glycoprotein I. With a thrombosis and a negative result, the cause is investigated further. According to the NVKC, in people with lupus (SLE) the test is repeated regularly.
Preparation
- Taking blood thinners (anticoagulants)? Do not stop, but say which medicine you use when your blood is taken; the lab needs this to assess the result.
If your result is abnormal
With a positive result, the test is repeated after at least 12 weeks, together with antibodies against cardiolipin and beta-2 glycoprotein I. If the result stays positive and there has been a thrombosis or pregnancy problem, the GP refers to an internist. With confirmed antiphospholipid syndrome after a thrombosis, the FMS guideline usually advises a coumarin over a DOAC, and with repeated early miscarriages, treatment with low-dose aspirin and heparin can be considered in a next pregnancy.
Reliability
The result mainly says something in people with a thrombosis at a young age or without a clear cause, with repeated miscarriages or with an autoimmune disease such as lupus. According to the FMS guideline, a positive result only counts if it is positive again after at least 12 weeks. The measurement is easily disturbed: anticoagulants can give a false-positive or uninterpretable result, and platelets left in the plasma a false-negative one. In people without thrombosis or pregnancy problems, a positive result is hard to interpret.
Limitations
- Anticoagulants disturb the measurement: coumarins, DOACs and heparin can give a false-positive or uninterpretable result. That is why the laboratory asks which anticoagulant you use.
- An infection and some medicines can make lupus anticoagulant temporarily positive; that is why a positive result is repeated after at least 12 weeks.
- The laboratory uses one test system (dRVVT); internationally, a combination of two different tests is recommended, so a negative result does not completely rule out lupus anticoagulant.
- The measurement requires plasma without platelets: the tube must be centrifuged twice and the plasma frozen; platelets left behind can give a false-negative result.
How common is this
According to the NVKC, an estimated 1 to 2 in 100 people make antibodies against phospholipids, but most have no problems from them. Antiphospholipid syndrome itself is rare. Lupus anticoagulant is more common in people with lupus (SLE) and temporarily after infections.
Who is this useful for
Useful with a thrombosis at a young age, in an unusual place or without a clear trigger, with repeated miscarriages or other pregnancy problems, with an unexplained prolonged aPTT and with lupus (SLE). The FMS guideline recommends testing women with at least three miscarriages before 10 weeks of pregnancy for lupus anticoagulant, together with antibodies against cardiolipin and beta-2 glycoprotein I. With the use of anticoagulants, the result often cannot be reliably interpreted. In people without such events, the predictive value is low and no treatment follows.
Downsides and risks
- With the use of anticoagulants, the result can be false-positive and cause needless worry or lead to unnecessary follow-up testing.
- A negative result can be falsely reassuring, because the laboratory uses one test system and antiphospholipid syndrome can also show up as other antibodies.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results