Seronegative APS (SN-APS)
The path to diagnose a disease is usually a straightforward one. The patient complains of symptoms then either has a blood test and/or scans, and these confirm the diagnosis.
APS blood tests
If your doctor suspects you may have APS, they should order the following three blood tests that look for antiphospholipid antibodies (aPL) in your blood:
- The anticardiolipin (aCL)
- The confusingly named lupus anticoagulant (LA)
- The anti-beta2-glycoprotein-1 (anti-B2GP1)
The first two tests have been used since the discovery of the condition, but the anti-B2GP1 test is more recent may not be carried out in all hospitals.
If any of the above tests are positive and indicate you have aPL in your blood, then you will be asked to repeat the blood tests within six to twelve weeks to confirm that you are positive.
What is seropositive/seronegative?
Seropositive and seronegative are terms that refer to the results of a blood test. If you are seropositive then your tests are positive and a firm diagnosis can, usually, easily be reached, but what if your results are negative and you still have the symptoms?
In other autoimmune conditions, such as rheumatoid arthritis and lupus, seronegativity is an accepted diagnosis and patients can be treated accordingly, but this is still a contentious issue where APS is concerned and there are two main possibilities:
- The diagnosis is wrong and the patient has a different condition.
- The current laboratory tests are not sensitive enough and fail to identify the antibodies in all patients. This concept is supported by the recent introduction of the anti-B2GP1, which yielded positive tests in patients who repeatedly had negative aCL and LA tests results. Research is still taking place to refine the aPL tests so even more accurate ones may be available in the future.
Confirming a diagnosis of seronegative APS (SN-APS) can be difficult as it is not officially recognised by many specialists. However, thanks to a piece of research undertaken by University College London (UCL) and St Thomas’ Hospital which was driven by our charity’s patient group, SN-APS is now becoming more accepted in the medical community.
The collaborative research project used a new laboratory test devised by Professor Rahman’s team at UCL, and found that 10% of patients who had previously had clear clinical symptoms of APS but always tested negative, did actually test positive for this new test. Please click here to read the abstract of the study which was published in the Annals of the Rheumatic Diseases in 2014.
As with conditions such as rheumatoid arthritis and lupus, a firm diagnosis of seronegativity can only be made when the patient meets the clinical criteria. Therefore, in the case of SN-APS, you would have to have clotting episodes and/or recurrent miscarriages or a stillbirth before such a diagnosis would be considered. The low grade symptoms of the condition such as headaches/migraines, fatigue, memory problems and arthralgia would not be taken into account as these can be attributed to many other causes.