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Antiphospholipid syndrome

2025/09/02

What is Antiphospholipid Syndrome (APS)?

Antiphospholipid Syndrome (APS) is a chronic autoimmune disorder. It occurs when the body's immune system (which usually protects the body from infections) produce abnormal antibodies known as antiphospholipid antibodies which increase risks of blood clots. These clots can occur in the veins and arteries (thrombotic APS) and/or lead to pregnancy complications (obstetric APS) such as recurrent miscarriages, severe high blood pressure during pregnancy (preeclampsia), insufficient blood flow to the placenta and premature delivery.

APS can occur on its own (primary APS) or alongside another autoimmune condition (secondary APS), most commonly Systemic Lupus Erythematosus (SLE).

What causes APS?

The exact cause of APS is not fully understood, but it is thought to be contributed by a complex relationship between genetic and environmental factors. A family history of autoimmune diseases can increase your risk. Environmental factors such as infections and medications may trigger the disease.

What are the symptoms of APS?

Symptoms can vary depending on where blood clots form and can be life-threatening in severe cases.

Thrombotic APS (blood clots):
• Deep vein thrombosis (DVT) – this occurs when blood clots develop in the veins in the limbs, leading to swelling, redness, and pain. The calves are most commonly affected.
• Pulmonary embolism – blood clots develop in the major artery (pulmonary artery) in the lungs. Patients may have shortness of breath, chest pain, raised heart rate and cough up blood. This can occur in tandem with DVT or as separate conditions. In severe cases, large pulmonary embolisms can lead to low blood pressure which can be dangerous.
• Stroke – blood clots develop in the arteries in the brain, and may lead to sudden numbness or weakness affecting one side of the body, double vision, incoordination or speech difficulties.
• Heart attack – blood clots in the major arteries supplying the heart (coronary arteries) can lead to a heart attack. Patients may present with chest pain, breathlessness, nausea and sweating.
• Blood clots may also occur in other parts of the body such as the blood vessels in the eyes, kidneys, liver and spleen.

Obstetric APS (pregnancy-related issues):
• Recurrent miscarriages, especially in the second or third trimester
• Preeclampsia – APS can cause high blood pressure in pregnancy. In severe cases, there can be injury to the liver and kidneys, low blood counts and low platelets (important component of blood which helps with clotting), and seizures (fits)
• Slow fetal growth
• Premature birth
• Stillbirth

Other features associated with APS include:
• Purplish rash (Livedo reticularis)
• Low platelet counts which may lead to easy bleeding and bruising
• Headaches due to migraines, abnormal body movements (chorea) and memory impairment
• Abnormalities with the heart valves which can lead to shortness of breath, leg swelling. An abnormal heart sound (murmur) may be heard with a stethoscope.

Not everyone will experience all of these symptoms. Some people may have no obvious symptoms but are diagnosed after testing due to unexplained pregnancy loss or blood clots.

How is APS diagnosed?

APS is diagnosed based on both clinical history and blood tests showing specific antiphospholipid antibodies. A detailed history and clinical examination will be performed. Investigations include:

• Blood tests including blood counts, kidney and liver tests and antiphospholipid antibodies (aPLs) – repeated at least 12 weeks apart. These aPLs include:

o Lupus anticoagulant
o Anticardiolipin antibodies (IgM and IgG)
o Anti-beta-2 glycoprotein I antibodies (IgM and IgG)

• Imaging scans may be performed if there are suggestive symptoms to detect clots (such as ultrasound, CT or MRI)

Presence of antiphospholipid antibodies without any history of blood clots or pregnancy complications is not confirmatory for APS.

As APS can occur with other autoimmune conditions such as SLE, further tests for other autoimmune conditions may be performed as appropriate depending on clinical suspicion.

What is the treatment for APS?

There is no cure for APS at present, but it can be well managed with medications and lifestyle modifications.

Thrombotic APS

• Patients with thrombotic APS will require long-term blood thinning medications (anticoagulation) to reduce the risk of recurrent blood clots.

o Warfarin is the most common medication used in APS. Regular blood tests will be performed to monitor warfarin levels (known as the international normalised ratio or INR) to ensure that the blood is not too thick or thin. Patients should maintain a consistent diet when taking warfarin as certain food can affect INR levels. Some medications and traditional herbs may also interact with warfarin and cause fluctuations in the INR. It is important to inform your healthcare providers that you are taking warfarin before starting any new medications as closer INR monitoring and dose adjustments may be required.
o Some patients may require heparin, a blood thinning medication given as injections under the skin (subcutaneous injection) when they are first started on warfarin, planned for any surgical procedures, or if they are unable to take warfarin.

• Aspirin (another blood thinning medication) may be added for certain patients with major blood clots in the arteries such as previous heart attack or strokes.
• Immune suppression medications may be required for patients with other autoimmune conditions in addition to APS

Obstetric APS

Patients with obstetric APS (pregnancy complications without any blood clots) do not require long-term anticoagulants except during pregnancy and in the first few weeks after delivery. Please see section below for more information.

Can I get pregnant if I have APS?

Many women with APS go on to have successful pregnancies with proper treatment. Pregnancy plans should be discussed early with the rheumatologist and close monitoring is required by an obstetrician trained in the management of high-risk pregnancies.

During pregnancy, patients with both thrombotic and obstetric APS will need to be on subcutaneous heparin injections to prevent blood clots and complications during pregnancy. Warfarin is not suitable during pregnancy as it can cause birth defects in the fetus.

In addition, patients with APS will need to be on aspirin to prevent pre-eclampsia (high blood pressure during pregnancy). Select patients may require additional medications such as hydroxychloroquine especially if they have other autoimmune conditions such as SLE.

What should I do if I have APS?

• Avoid smoking as it increases risks of blood clots
• Eat a balanced and consistent diet – certain food and dietary changes can affect INR levels.
• Stay active and avoid sitting for long periods – sitting for prolonged periods can increase the risk of blood clots, e.g. during long flights.
• Regular exercise is recommended. Contact sports should be avoided while on anticoagulation to prevent bleeding complications.
• Inform all healthcare providers that you have APS, especially if you are taking warfarin as certain medications may interact with warfarin. If planned for an elective surgery, discuss with your surgeon and rheumatologist early as warfarin may need to be stopped and switched to subcutaneous heparin temporarily.
• Take medications regularly as prescribed, even when you feel well.
• Attend regular medical check-ups to monitor your health. Participate actively in your care and ask questions during your clinic consultations
• Discuss contraception with your rheumatologist and gynaecologist – certain birth control medications are not appropriate for patients with APS as they may increase risk of blood clots.
If pregnant or trying to conceive, inform your rheumatologist early and see an obstetrician who specializes in high-risk pregnancies.

What should I do if I suspect I have APS?

Seek a doctor's advice. You will be referred to a specialist (rheumatologist) who can confirm the diagnosis and start you on the appropriate treatment.

This condition is managed by the Division of Rheumatology and Allergy. The division also runs a High Risk Pregnancy Clinic for patients with APS and other rheumatic disease who are pregnant, planning to conceive or are undergoing assisted reproductive treatments. Close partnership with Obstetrics is maintained throughout pregnancy and peri-partum to optimise care.