Antiphospholipid Syndrome (APS)

Meet the patient

A 32-year-old woman is admitted with a swollen left calf, breathless on the stairs, and a pregnancy test that comes back positive at seven weeks. Her APTT is 52 seconds and does not correct on the mixing study. Two years ago she lost a pregnancy at 16 weeks with severe pre-eclampsia, and she has a malar rash she blames on the sun.[2]

Two questions decide her admission, and they decide every APS case you will ever see: is that prolonged APTT a bleeding risk or a clotting risk? and what anticoagulant do I use, for how long, and is it safe in pregnancy? Hold those two questions and the rest of this page slots into place.[1]

What APS actually is — and the paradox that defines it

APS is the only thrombophilia that is both a clotting disease and an obstetric disease. It is an acquired, autoimmune, prothrombotic state driven by persistent antiphospholipid antibodies — lupus anticoagulant, anticardiolipin, anti-beta-2-glycoprotein-I — that bind phospholipid-binding proteins and ignite thrombosis in any vessel, and strike the placenta besides.[2]

Graham Hughes described it in 1983 in lupus patients with a circulating anticoagulant, recurrent thrombosis, and recurrent miscarriage. It is now the most common acquired thrombophilia and the leading treatable cause of recurrent pregnancy loss — two titles no other thrombophilia holds.[2]

The lupus anticoagulant paradox is the single most examinable idea in the disease — so learn it as the mantra: prolongs in vitro, clots in vivo. The antibody lengthens phospholipid-dependent clotting times in the test tube, yet in the living patient it is relentlessly prothrombotic.[2]

The classic trap: misreading that prolonged APTT as a bleeding tendency and withholding anticoagulation. The patient is not about to bleed — they are about to clot. Prove the lupus anticoagulant, then anticoagulate.[2]

Three faces of APS — primary, secondary, catastrophic

APS sorts along two axes: definite versus probable, and primary versus secondary. The first axis is the revised Sapporo classification (Miyakis 2006) — one clinical criterion plus one laboratory criterion, the antibody persistent on two occasions at least twelve weeks apart. The second separates primary APS, with no underlying autoimmune disease and the majority of cases, from secondary APS, most often to systemic lupus erythematosus.[1]

Antibodies that flicker up transiently after an infection or a drug are not APS — persistence is the dividing line, and that is exactly why the twelve-week rule exists.[1]

The Sapporo rule — one clinical plus one lab, twelve weeks apart

Definite APS needs at least one clinical and at least one laboratory criterion. There is no upper time limit between the clinical event and the positive test, and coexisting autoimmune disease is permitted. The antibody must be persistent — present on two or more occasions at least twelve weeks apart, and no more than five years from the clinical event.[1]

Clinical criteria (need one): [1]

1. Vascular thrombosis — one or more clinical episodes of arterial, venous, or small-vessel thrombosis in any tissue or organ, confirmed by objective validated imaging or histology. Histopathologically, thrombosis must be present without significant inflammation in the vessel wall (this excludes vasculitis).
2. Pregnancy morbidity, defined as any one of:
   • (a) One or more unexplained deaths of a morphologically normal fetus at or beyond 10 weeks of gestation; OR
   • (b) One or more premature births of a morphologically normal neonate before 34 weeks because of (i) eclampsia or severe pre-eclampsia (standard definitions) or (ii) recognised features of placental insufficiency (abnormal Doppler, oligohydramnios, intrauterine growth restriction, abnormal fetal heart tracing); OR
   • (c) Three or more unexplained consecutive spontaneous abortions before 10 weeks, with maternal anatomic or hormonal abnormalities and parental chromosomal causes excluded.[1]

Laboratory criteria (need one): [1]

1. Lupus anticoagulant (LA) present in plasma, on two or more occasions at least 12 weeks apart, detected by the International Society on Thrombosis and Haemostasis (ISTH) algorithm — a phospholipid-dependent clotting test that is prolonged, does not correct on a mixing study, and does correct on confirmation with excess phospholipid.
2. Anticardiolipin (aCL) antibody of IgG and/or IgM isotype in medium or high titre — over 40 GPL units or MPL units, or above the 99th percentile — on two or more occasions at least 12 weeks apart.
3. Anti-beta-2-glycoprotein-I antibody of IgG and/or IgM isotype in units above the 99th percentile, on two or more occasions at least 12 weeks apart, by standardised ELISA.[1]

The 2023 ACR/EULAR criteria (Barbhaiya) build on Sapporo with a weighted score that captures extra antiphospholipid-antibody specificities and refines the obstetric phenotypes. They are intended chiefly as research entry criteria, but they reinforce the same core — persistent lupus anticoagulant, high-titre anticardiolipin or anti-beta-2-glycoprotein-I, and a compatible clinical event.[4]

Who clots — the carrier, the thrombosis, the trigger

Antibody positivity alone is not APS. Antiphospholipid antibodies drift through 1 to 5 percent of healthy adults and 3 to 10 percent of blood donors, and most of those people never clot. The syndrome needs the clinical picture plus persistent antibodies — and the commonest over-diagnosis error is labelling APS from a single low-titre antibody, often after a viral illness.[2]

• Incidence and prevalence of APS: estimated annual incidence around 1 to 2 new cases per 100,000 and prevalence around 40 to 50 per 100,000, although true figures are uncertain because testing is inconsistent. APS accounts for a meaningful share of young-adult thrombosis — it underlies roughly 10 to 15 percent of all deep vein thrombosis (DVT) and 10 to 25 percent of strokes in patients under 50.[2]
• Secondary APS and SLE: up to 30 to 40 percent of SLE patients carry antiphospholipid antibodies; roughly half of antibody-positive SLE patients thrombose over a 20-year follow-up, making SLE the single most important associated condition and the one every examiner expects you to name.
• Age and sex: APS predominates in young women (reflecting SLE epidemiology and the obstetric presentation), with a female-to-male ratio of roughly 3.5 to 1 in primary APS and higher in secondary. It nonetheless occurs in either sex and at any age; the male with idiopathic DVT should be tested.
• Thrombotic risk is antibody-dependent: lupus anticoagulant positivity carries the highest thrombotic risk of the three antibodies (odds ratios for thrombosis consistently two- to four-fold higher than aCL). Triple-positive patients (LA, aCL and anti-beta-2-GPI all positive) carry the greatest recurrence risk and are the group in whom DOACs must be avoided.[3]
• Catastrophic APS is rare — under 1 percent of APS — but has 30 to 50 percent mortality, the emergency end of the spectrum.[5]
• Other risk factors that amplify risk in antibody carriers: oestrogen-containing oral contraception and hormone replacement, pregnancy and the puerperium, surgery, immobility, smoking, malignancy, nephrotic syndrome, and active lupus. The clinician's job in an asymptomatic carrier is risk attenuation — stop oestrogens, treat hypertension, control SLE.

Why the paradox — antibodies that bind, activate, and clot

The antibodies are directed not at phospholipid itself but at phospholipid-binding plasma proteins — chiefly beta-2-glycoprotein-I (apolipoprotein H) and prothrombin. When the antibody docks beta-2-glycoprotein-I onto endothelium, platelets, monocytes and trophoblasts, cell-surface receptors recognise the complex and switch those cells on.[2]

The switched-on cell then drives a prothrombotic cascade — and each limb is a drug target or a viva answer:[1]

• Endothelial activation — upregulation of tissue factor, adhesion molecules (E-selectin, ICAM-1, VCAM-1) and von Willebrand factor, converting the vessel wall from anticoagulant to procoagulant.
• Platelet activation — cross-linking of Fc-gamma receptors and glycoprotein Ib/IX promotes platelet aggregation and thromboxane A2 release.
• Monocyte activation — tissue-factor and cytokine (interleukin-1, tumour necrosis factor) expression amplifies the coagulation cascade.
• Complement activation — particularly C5a and the membrane attack complex, which recruit neutrophils and amplify endothelial injury; complement is now recognised as central to both thrombosis and placental damage.
• Coagulation cascade amplification — interference with the protein C/S anticoagulant pathway, annexin A5 shield disruption, and direct activation of factor X and prothrombinase complexes. [1]

This is where the paradox lives. The same antibody interferes with phospholipid-dependent tests in vitro — the APTT and the dilute Russell viper venom time are prolonged, fail to correct on a mixing study because the inhibitor persists in the mixture, yet correct when excess phospholipid is added — while in vivo it is prothrombotic.[2]

At the placenta the disease is thrombotic and complement-driven. Antibody-bound beta-2-glycoprotein-I on trophoblasts triggers complement deposition, trophoblast injury, defective placentation and placental microvascular thrombosis — the mechanism behind recurrent early loss, late fetal death and the severe pre-eclampsia that define obstetric APS. This is why aspirin plus heparin rescues pregnancy, and why warfarin, which is teratogenic, cannot be used.[2]

Three ways APS walks onto the ward — vein, artery, placenta

APS presents as thrombosis, as pregnancy morbidity, or — rarely — as catastrophic multi-organ failure. The asymptomatic antibody carrier is not APS by definition, but is the population in whom primary prevention matters.[1]

Venous thrombosis is the commonest manifestation — about two-thirds of thrombotic events — and lower-limb DVT with pulmonary embolism dominates. What marks APS out is that almost any venous bed can clot: cerebral venous sinus, portal, hepatic (Budd-Chiari), renal, retinal, and adrenal vein thrombosis causing haemorrhagic adrenal infarction and Addisonian crisis. Recurrent DVT at multiple sites despite adequate anticoagulation should trigger testing.[2]

Arterial thrombosis is where APS leaves the inherited thrombophilias behind — they are overwhelmingly venous. Stroke or transient ischaemic attack in a patient under 50 is the classical arterial event and a favourite exam stem; APS underlies a substantial minority of so-called cryptogenic young strokes. Myocardial infarction, mesenteric and renal artery occlusion, and retinal artery occlusion round out the arterial list, and arterial events tend to recur arterially.[2]

Pregnancy morbidity takes the three Sapporo forms. Three or more unexplained consecutive miscarriages before ten weeks; one or more unexplained fetal deaths at or beyond ten weeks of a morphologically normal fetus; or severe pre-eclampsia, eclampsia or placental insufficiency needing delivery before 34 weeks. A history that mixes recurrent early loss with a late stillbirth is highly suggestive.[1]

Non-criteria features support the diagnosis without defining it:[1]

• Haematological — mild thrombocytopenia (around 30 percent of patients; usually 100 to 150 x 10⁹ per litre and rarely bleeding), rare autoimmune haemolytic anaemia.
• Skin — livedo reticularis and livedo racemosa (broken, branching cyanosis — livedo racemosa is the more irregular, non-uniform form more strongly associated with APS), cutaneous ulceration, splinter haemorrhages, necrotising vasculitis-like lesions.
• Cardiac — cardiac valve thickening and Libman-Sacks verrucous endocarditis (mostly aortic and mitral valves), accelerated atherosclerosis, intracardiac thrombi.
• Neurological — besides stroke, migraine, cognitive dysfunction, seizures, chorea, transverse myelitis, and the "Sneddon syndrome" triad of livedo plus stroke plus hypertension.
• Renal — APS nephropathy: vaso-occlusive lesions of the intrarenal vessels producing hypertension, proteinuria and chronic kidney disease, histologically thrombotic microangiopathy and fibrous intimal hyperplasia. [1]

Catastrophic APS is the emergency end of the spectrum — and the passage where the jokes stop. It is defined by rapid development of multiple thromboses over days, leading to multi-organ failure — microvascular thrombosis in kidneys, brain, lungs, skin, heart and gut all at once, with thrombocytopenia, schistocytes and frequent DIC overlap. Diagnostic criteria demand three or more organs involved simultaneously or within a week, histopathological small-vessel occlusion, and antiphospholipid-antibody positivity. It is usually triggered — by infection in about half of cases, also surgery, withdrawal of anticoagulation, obstetric complications or malignancy — and it carries a 30 to 50 percent mortality.[5]

The differential fork — inherited, acquired, APTT mimics

Three differentials decide the APS work-up: inherited thrombophilia, other acquired hypercoagulable states, and the causes of a prolonged APTT.[1]

[1]

When CAPS is suspected, separate it from three look-alikes: sepsis with disseminated intravascular coagulation, thrombotic microangiopathy (haemolytic uraemic syndrome, or thrombotic thrombocytopenic purpura with ADAMTS13 under 10 percent), and HELLP syndrome. All share microvascular thrombosis and thrombocytopenia; only CAPS carries the antiphospholipid-antibody background, the small-vessel occlusion without vasculitis on histology, and the combined immunomodulation-plus-anticoagulation response.[1]

The bedside round — no pathognomonic sign, hunt the clues

There is no pathognomonic bedside sign of APS. Assessment is that of the thrombotic event itself, plus a structured hunt for clues, for complications, and for an underlying autoimmune disease.[1]

Venous event: examine for calf swelling, tenderness, erythema, warmth; measure the calf-circumference difference (over 3 cm is significant); apply the Wells score for DVT. For suspected pulmonary embolism, look for tachycardia, tachypnoea, hypoxia, pleuritic pain, and right-heart strain; apply the Wells or revised Geneva score and obtain D-dimer and CT pulmonary angiography. [1]

Arterial event: a focal neurological deficit (face/arm weakness, aphasia, visual field loss) suggests stroke — urgent CT or MRI brain; abdominal pain and bloody stools suggest mesenteric thrombosis; flank pain and new hypertension suggest renal artery or vein thrombosis; sudden limb ischaemia is an emergency. [1]

Skin: inspect for livedo reticularis and racemosa (reticulate cyanosis, especially over the thighs, knees, arms), cutaneous ulcers, splinter haemorrhages, digital gangrene, and cutaneous necrosis. [1]

Cardiac: auscultate for new murmurs of Libman-Sacks endocarditis (mitral or aortic regurgitation from verrucous vegetations) or valve thickening; an echocardiogram confirms. [1]

Autoimmune screen: look for SLE features — malar (butterfly) rash, discoid rash, oral or nasal ulcers, photosensitivity, arthritis, serositis, alopecia, Raynaud phenomenon — which mark secondary APS and change management (add hydroxychloroquine). Check for lymphadenopathy and organomegaly to exclude occult malignancy. [1]

Obstetric history: document the number, gestation and outcome of every pregnancy — miscarriages (with weeks of gestation and whether fetal heart was seen), fetal losses, pre-eclampsia or HELLP, gestation at delivery, indications for premature delivery, birthweights, and any neonatal deaths. The Sapporo obstetric criteria are quantitative, so precise records matter. [1]

General examination: blood pressure (renal involvement, APS nephropathy), urine dipstick (proteinuria), and signs of other risk factors (smoking, obesity, varicose veins). [1]

The ISTH four-step lupus anticoagulant algorithm — SMCE

Definite APS needs one clinical plus one laboratory criterion, the antibody persistent on two occasions at least twelve weeks apart. Always exclude transient causes — recent infection, drugs — and repeat abnormal results before labelling anyone. A single positive result is never APS.[1][2]

The lupus anticoagulant is run through the ISTH four-step algorithm — Screen, Mix, Confirm, Exclude (SMCE). First, screen: a phospholipid-dependent clotting test (APTT, dRVVT, kaolin clotting time, or dilute prothrombin time) is prolonged. Second, mix: it fails to correct on a 1:1 mixing study with normal pooled plasma, proving an inhibitor rather than a factor deficiency. Third, confirm: the prolongation corrects when excess phospholipid is added, proving the inhibitor is phospholipid-dependent. Fourth, exclude: rule out heparin contamination and specific factor inhibitors.[1]

Timing decides whether the result means anything. Antibodies can flicker positive after infection (especially viral illness, syphilis, HIV, hepatitis C) and after drugs (chlorpromazine), so confirm persistence at least twelve weeks later — the persistence rule exists precisely to exclude these. Never diagnose APS from a single result, and avoid testing in the middle of an acute thrombotic event when acute-phase and heparin effects can give false negatives. When the APTT is prolonged, always run a mixing study and, if it does not correct, a phospholipid correction step — that sequence is the signature of lupus anticoagulant and the most examinable laboratory algorithm in the disease.[1]

Acute APS — treat the event, suspect CAPS early

APS itself is not the emergency — the event it has caused is — with one life-threatening exception: catastrophic APS. Treat the thrombosis or pregnancy complication first, and confirm APS in parallel.[1]

• Acute VTE: weight-based low-molecular-weight heparin (LMWH) — for example enoxaparin 1 mg per kg subcutaneously every 12 hours — then transition to warfarin once the patient is stable and the INR is in range. Unfractionated heparin is an alternative if rapid reversibility is needed (renal failure, recent surgery). Massive PE with haemodynamic instability → thrombolysis (alteplase) or surgical/catheter embolectomy by the pulmonary embolism response team.
• Acute arterial event (e.g. large-vessel ischaemic stroke): urgent imaging (CT then MRI), intravenous thrombolysis (alteplase) if within the time window and no contraindication, mechanical thrombectomy if eligible, then therapeutic heparin and vascular-team input. APS itself is not a contraindication to thrombolysis.
• Catastrophic APS (CAPS) — a medical emergency requiring combined therapy without delay: therapeutic anticoagulation (heparin/LMWH unless bleeding contraindicates), high-dose corticosteroids (e.g. methylprednisolone 1 g intravenously daily for three to five days), plasma exchange (3 to 6 sessions over 5 to 8 days, replacing with fresh-frozen plasma), and intravenous immunoglobulin (IVIG) 0.4 g per kg daily for four to five days. Identify and aggressively treat triggers — infection is the commonest, also surgery, withdrawal of anticoagulation, malignancy, and obstetric complications. Provide critical-care organ support (renal replacement therapy, ventilation, vasopressors). Refractory cases may need rituximab (anti-CD20 B-cell depletion) or the terminal complement inhibitor eculizumab (anti-C5), particularly when there is a strong complement signal.[2][5]

Lifelong warfarin, not DOACs — the TRAPS lesson

Once the acute event is controlled, APS management is lifelong and risk-stratified. The commonest exam error is reaching for a DOAC, or stopping anticoagulation after a finite course — APS thrombosis recurs, often in the same vascular bed, and at a higher rate than non-APS thrombosis.[1][2]

The DOAC trap — straight, no jokes. The TRAPS trial (Pengo 2018) randomised high-risk, triple-positive APS patients to rivaroxaban versus warfarin and was stopped early because rivaroxaban carried an excess of arterial thrombotic events against warfarin. Subsequent apixaban observational data are not robust enough to overturn it. Warfarin remains the preferred anticoagulant for definite APS, especially triple-positive or arterial disease; a DOAC is reasonable only in low-risk APS (a single positive antibody, an isolated provoked VTE) where warfarin is truly not feasible, and even then only with specialist input.[3]

Adjuncts to know by name. Hydroxychloroquine reduces thrombosis risk and is recommended in SLE-associated APS (200 to 400 mg daily by mouth, weight-based to avoid retinal toxicity), and is increasingly used in refractory disease regardless of SLE status. Statins add a pleiotropic anti-inflammatory effect; rituximab (anti-CD20) is reserved for refractory thrombosis or autoimmune cytopenias; eculizumab (terminal complement blockade) is emerging in refractory CAPS and in renal transplant in APS.[1]

The pregnancy protocol — aspirin plus heparin, warfarin is teratogenic

This is a viva-classic and the preventable-harm passage — reproduce it exactly.[1]

1. Pre-conception counselling — confirm APS diagnosis with persistent antibodies; switch from warfarin to aspirin plus LMWH before conception (warfarin is teratogenic, especially weeks 6 to 12).
2. Aspirin 75 mg daily — started at confirmation of a positive pregnancy test, ideally pre-conception; continued throughout pregnancy.
3. LMWH — commenced once fetal heart is confirmed (around 6 to 7 weeks) to minimise early-pregnancy bleeding; prophylactic enoxaparin 40 mg subcutaneously daily if no prior thrombosis, treatment-dose enoxaparin 1 mg per kg twice daily if prior VTE; continued to delivery.
4. Anticoagulant monitoring — anti-Xa levels in renal impairment or at extremes of weight; full blood count for heparin-induced thrombocytopenia; bone-density awareness with prolonged heparin.
5. Fetal surveillance — serial growth scans and umbilical artery Doppler from 20 to 24 weeks; biophysical profile in the third trimester; planned delivery at 37 to 39 weeks (earlier if pre-eclampsia or growth restriction).
6. Peripartum — stop LMWH 24 hours before planned delivery or induction to allow neuraxial anaesthesia (ASRA guidance: 12 hours after last prophylactic LMWH, 24 hours after last treatment-dose); resume heparin postpartum.
7. Postpartum — switch to warfarin (safe in lactation) with LMWH overlap until INR is in range for at least two consecutive days; continue warfarin for a minimum of 6 weeks postpartum, longer if prior thrombosis (lifelong). Aspirin usually continued.
8. Refractory obstetric APS — IVIG 0.4 g per kg daily for 4 to 5 days, plasma exchange, or hydroxychloroquine plus low-dose prednisolone in the first trimester for selected cases. [1]

With this regimen, live-birth rates in obstetric APS exceed 70 percent — transforming a previously bleak prognosis.[2]

Preventable harm: warfarin in pregnancy is teratogenic, especially in weeks 6 to 12 — every APS patient of reproductive age must switch from warfarin to aspirin plus LMWH before conception. Finding a patient still on warfarin at the booking visit is a failure of pre-conception counselling, not of obstetrics.[1]

Subtypes that change the plan

Each subtype bends the plan in one specific way. Read the list as decisions, not definitions.[1]

• Primary APS — no underlying autoimmune disease; the majority of cases; managed with lifelong anticoagulation as above. The antibody profile and prognosis are similar to secondary APS once a thrombosis has occurred.
• Secondary APS (SLE) — add hydroxychloroquine 200 to 400 mg daily; screen all SLE patients for antiphospholipid antibodies at diagnosis; control disease activity; treat hypertension and dyslipidaemia; avoid oestrogen-containing contraception and hormone replacement; vaccinate (influenza, pneumococcus, COVID-19) and treat infections promptly (triggers of CAPS).
• Catastrophic APS (CAPS) — under 1 percent of APS but 30 to 50 percent mortality; combined anticoagulation plus corticosteroids plus plasma exchange plus IVIG; treat triggers aggressively; consider rituximab or eculizumab if refractory; survivors need lifelong warfarin at higher INR targets.
• Obstetric APS — recurrent miscarriage, late fetal loss, severe pre-eclampsia/HELLP, placental insufficiency; aspirin plus heparin dramatically improves live-birth rate (from under 20 percent untreated to over 70 percent). Distinguish from "non-criteria obstetric APS" (early losses not meeting Sapporo) where benefits of treatment are less certain.
• Triple-positive APS (LA, aCL and anti-beta-2-GPI all positive) — highest recurrence risk; warfarin at higher INR, not DOACs; consider hydroxychloroquine.
• Seronegative APS — clinical phenotype with repeatedly negative standard antibodies; antibodies to non-criteria antigens may explain some; specialist input, treatment individualised.
• Microvascular APS / Sneddon syndrome — livedo racemosa plus stroke plus hypertension; managed as APS with anticoagulation plus antiplatelet and aggressive vascular risk-factor control. [1]

Complications and the classic pitfalls

The recurring pitfalls every candidate must name — the table holds them, and the examiner expects them.[1]

Prognosis and disposition

APS demands lifelong anticoagulation after a thrombotic event, and the recurrence risk is higher than for non-APS thrombosis — arterial events recur arterially and venous events venously. The 10-year prospective cohort of 1000 APS patients (Cervera 2015) showed substantial further thrombosis and measurable mortality despite treatment; triple-positive status conferred the highest future risk.[5]

With aspirin plus heparin, most obstetric APS pregnancies reach live birth (over 70 percent). Catastrophic APS mortality sits at 30 to 50 percent; survivors need aggressive long-term anticoagulation and close surveillance, with a high risk of further thrombosis and chronic organ damage. The burden of lifelong anticoagulation — INR monitoring, bleeding risk, the dietary and drug interactions of warfarin — weighs on quality of life alongside recurrent pregnancy loss and the chronic uncertainty of autoimmune disease.[1]

Disposition is outpatient anticoagulation under a haematology or thrombosis clinic, combined obstetric-haematology care in pregnancy, rheumatology input for SLE-associated disease, and a low threshold to hospitalise any rapidly deteriorating patient — suspect CAPS. Every patient should carry a medical-alert indicating APS and anticoagulation.[1]

Special populations

Presentation, reperfusion, and bleeding risk all shift in these groups — examiners reach for them on NEET-PG and INICET.[1]

• Pregnancy + APS: stop warfarin pre-conception (teratogenic, especially weeks 6 to 12) and use low-dose aspirin plus prophylactic or treatment-dose LMWH throughout pregnancy and for 6 weeks postpartum; DOACs avoided (insufficient safety data); plan delivery around neuraxial anaesthesia and anticoagulation timing (ASRA guidance); combined obstetric-haematology care with serial fetal surveillance.
• SLE: screen all SLE patients for antiphospholipid antibodies at diagnosis and re-test if thrombosis or pregnancy loss; aspirin plus hydroxychloroquine for antibody-positive patients; avoid oestrogen-containing contraception; lifelong anticoagulation after any thrombosis; treat hypertension, dyslipidaemia and active lupus.
• Children and adolescents: APS in the young is often post-infectious (transient) — confirm persistence; weigh the lifelong anticoagulation decision carefully; school and sport counselling.
• Elderly: first-presentation APS is rare beyond 60 — look hard for malignancy and other acquired causes; balance bleeding risk against thrombotic risk in anticoagulation.
• Anticoagulated / peri-operative: bridge warfarin with LMWH for surgery; never discontinue anticoagulation in APS without a plan (withdrawal is a CAPS trigger); coordinate with the surgical, anaesthetic and haematology teams.
• Renal impairment: LMWH dose-adjust by anti-Xa or use unfractionated heparin; eculizumab dosing requires meningococcal vaccination.
• Asymptomatic antibody carriers: no routine anticoagulation; address modifiable thrombotic risk (avoid oestrogens, stop smoking, control blood pressure and diabetes); aspirin considered in high-risk profiles (SLE, triple-positive). [1]

Evidence, guidelines and the regional deltas

Diagnosis rests on the revised Sapporo classification (Miyakis 2006) — one clinical plus one lab criterion, the antibody persistent at least twelve weeks apart. The 2023 ACR/EULAR criteria (Barbhaiya) retain the core but add a weighted score with extra antiphospholipid-antibody specificities and refined obstetric phenotypes; intended chiefly for research entry, they are increasingly used clinically.[1][4]

The TRAPS trial (Pengo 2018, Blood) randomised triple-positive APS patients to rivaroxaban versus warfarin and was stopped early for an excess of events with rivaroxaban — the single trial that cemented warfarin as preferred in high-risk APS, and the most examinable randomised evidence in the disease. Subsequent ASTRO-APS (apixaban) and RAPS (rivaroxaban) observational data do not overturn it.[3]

Obstetric management follows ASH 2018, BSH, and ACOG/RCOG guidance — low-dose aspirin plus prophylactic or treatment-dose LMWH in pregnancy, with six weeks of postpartum anticoagulation. The 1000-patient Euro-Phospholipid cohort (Cervera 2015) remains the definitive prospective description of morbidity and mortality.[5]

[1] [1] [1]

The memory devices — mantra, mnemonics, red flags

The mantra, repeated until it is reflex: prolongs in vitro, clots in vivo. When the APTT is prolonged and does not correct, think clotting, not bleeding — then prove the lupus anticoagulant and anticoagulate.[2]

[1]

Ward-round test — three stems, thirty seconds each

Three stems, a model answer in each Reveal. Cover the stem, answer out loud, then open it.[1]

Stem 1 — the prolonged APTT in pregnancy (answer)

A 32-year-old woman at seven weeks gestation has a DVT and an APTT of 52 seconds that does not correct on mixing. Two years ago she lost a pregnancy at 16 weeks with severe pre-eclampsia. What is the diagnosis, and what anticoagulation do you start? Model: This is antiphospholipid syndrome — recurrent pregnancy morbidity plus a thrombotic event plus a prolonged APTT that does not correct on mixing (the lupus anticoagulant signature). Confirm with the full antiphospholipid panel (lupus anticoagulant, anticardiolipin, anti-beta-2-glycoprotein-I), persistent on two occasions at least twelve weeks apart (revised Sapporo). In pregnancy, stop warfarin (teratogenic) and start aspirin 75 mg daily plus treatment-dose LMWH (enoxaparin 1 mg per kg twice daily) — she has a current thrombosis — continued throughout pregnancy and for at least six weeks postpartum, then transition to lifelong warfarin. Screen for SLE (ANA, anti-dsDNA, complement) and add hydroxychloroquine if lupus is present.[1][2]

Stem 2 — the young man with an unprovoked clot (answer)

A 28-year-old man presents with an unprovoked proximal DVT. His APTT is prolonged and does not correct on a mixing study but corrects with excess phospholipid. What is the diagnosis, and what is the first management decision that will mark him for life? Model: This is the lupus anticoagulant pattern — screen (prolonged phospholipid-dependent test), mix (fails to correct, proving an inhibitor), confirm (corrects with excess phospholipid, proving phospholipid-dependence), exclude (heparin and factor inhibitors) — the ISTH SMCE algorithm. Confirm persistence at twelve weeks before labelling definite APS. The lifelong decision: this is lifelong anticoagulation with warfarin, not a DOAC, and not a finite course. The classic trap is misreading the prolonged APTT as a bleeding tendency and withholding anticoagulation — he is a clotter, not a bleeder.[1][2]

Stem 3 — the known APS patient who stops warfarin and crashes (answer)

A 40-year-old with known triple-positive APS on warfarin stopped it 48 hours ago for a tooth extraction. She returns confused, with falling platelets, rising creatinine, and dusky livedo across her limbs. What is this, and what is the bundle in the next hour? Model: This is catastrophic APS (CAPS) — rapid multi-organ microvascular thrombosis with thrombocytopenia in a known APS patient, triggered here by withdrawal of anticoagulation. Treat empirically and do not wait: therapeutic anticoagulation (heparin or LMWH), high-dose corticosteroids (methylprednisolone 1 g intravenously daily for three to five days), plasma exchange (3 to 6 sessions over 5 to 8 days), and intravenous immunoglobulin 0.4 g per kg daily for four to five days — combined therapy, in parallel, in critical care. Hunt and treat the trigger aggressively. Mortality is 30 to 50 percent, so the cost of delay is the patient. This is the passage where the jokes stop.[1][5]

Rapid viva checklist

Reproduce this sequence from memory before you walk into any APS viva:[1]

1. Definition plus primary versus secondary to SLE
2. Pathophysiology chain — antibody binds beta-2-glycoprotein-I, activates cell, clots
3. The lupus anticoagulant paradox and the ISTH SMCE algorithm
4. Revised Sapporo 2006 — one clinical plus one lab, twelve weeks apart
5. Acute bundle for the thrombotic event
6. Definitive therapy with doses — warfarin INR 2 to 3 venous, 3 to 4 or plus aspirin arterial
7. The pregnancy protocol — aspirin 75 mg plus LMWH, warfarin teratogenic
8. Catastrophic APS — anticoagulation plus steroids plus plasma exchange plus IVIG
9. Guideline and trial names — Miyakis 2006, TRAPS (Pengo 2018), Barbhaiya 2023, Cervera 2015
10. The classic trap — do not misread the prolonged APTT as a bleeding tendency [1]

References

1. [1]Miyakis S, Lockshin MD, Atsumi T, et al. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS) J Thromb Haemost, 2006.PMID 16420554
2. [2]Knight JS, Branch DW, Ortel TL. Antiphospholipid syndrome: advances in diagnosis, pathogenesis, and management BMJ, 2023.PMID 36849186
3. [3]Pengo V, Denas G, Zoppellaro G, et al. Rivaroxaban vs warfarin in high-risk patients with antiphospholipid syndrome Blood, 2018.PMID 30002145
4. [4]Barbhaiya M, Zuily S, Naden R, et al. The 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria Arthritis Rheumatol, 2023.PMID 37635643
5. [5]Cervera R, Serrano R, Pons-Estel GJ, et al. Morbidity and mortality in the antiphospholipid syndrome during a 10-year period: a multicentre prospective study of 1000 patients Ann Rheum Dis, 2015.PMID 24464962