Diagnosis of Antiphospholipid Syndrome: A Comprehensive Guide

Introduction

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder marked by the persistent presence of antiphospholipid antibodies (APLAs). These autoantibodies target phospholipid-binding proteins, leading to a heightened risk of both arterial and venous thrombosis, as well as pregnancy complications. Accurate Diagnosis Of Antiphospholipid Syndrome is crucial for effective management and preventing severe outcomes. APS can manifest in various ways, from blood clots in the limbs and brain to recurrent pregnancy losses. This condition, while complex, requires a systematic approach for proper evaluation and treatment. Understanding the diagnostic criteria and procedures is paramount for healthcare professionals in managing patients potentially affected by APS.

Etiology of Antiphospholipid Syndrome

Antiphospholipid syndrome can arise in two primary forms: primary APS, occurring independently, and secondary APS, associated with underlying autoimmune conditions, most notably systemic lupus erythematosus (SLE), present in approximately 40% of cases. Studies reveal APLAs in a significant portion of diverse patient populations, including pregnant women (6%), stroke patients (13.5%), and individuals with deep vein thrombosis (DVTs) (9.5%).

Genetic predispositions, such as coagulation factor mutations and specific HLA alleles (HLA-DR7, DR4, DRw53, DQw7, and C4 null alleles), can elevate the susceptibility to APS-related thrombosis. Infections, particularly viral infections like Borrelia burgdorferi, hepatitis C, HIV, COVID-19, and Epstein-Barr virus (EBV), have been linked to increased APLA levels. Notably, a meta-analysis indicated that nearly half of COVID-19 patients tested positive for APS, predominantly lupus anticoagulant, though without a confirmed increased thrombotic risk in these cases.

Certain medications, including chlorpromazine, procainamide, quinidine, and phenytoin, can also trigger APLA production. Transient or low levels of APLAs may occur normally, necessitating repeat positive antibody tests at least 12 weeks apart for a definitive APS diagnosis.

APS classification further distinguishes between obstetric, thrombotic, or combined clinical presentations, and whether the condition involves life-threatening multiorgan involvement. Obstetric APS is diagnosed based on pregnancy morbidities such as premature birth due to preeclampsia, fetal death after 10 weeks, placental insufficiency, or recurrent embryonic losses before 10 weeks, alongside persistent APLA laboratory criteria.

Epidemiology of Antiphospholipid Syndrome

In the United States, the estimated incidence of antiphospholipid syndrome is approximately 2.1 per 100,000 individuals, with a prevalence of 50 per 100,000. Europe reports slightly lower rates, with an incidence of 1.1 per 100,000. Asian populations are believed to have even lower rates, with South Korea reporting an incidence of 0.75 per 100,000 and a prevalence of 6.19 per 100,000.

Low levels of anticardiolipin antibodies can be detected in up to 10% of healthy individuals, and the likelihood of a positive APLA test increases with age. A study of centenarians without autoimmune diseases showed a high prevalence of APLAs, with 54% positive for anti-β2GPI-IgG and 21% for anticardiolipin-IgG, although lupus anticoagulant was not detected, suggesting it might be a more specific marker. However, high titers and persistent positivity are uncommon in healthy individuals, occurring in less than 1%.

Patients with SLE face a significantly higher risk of positive APLA tests and related clinical outcomes like thrombosis or pregnancy complications, with 50% to 70% of SLE patients with positive APLA progressing to APS. APLA positivity is also observed in up to 20% of rheumatoid arthritis patients. In couples with recurrent abortions, around 20% tested positive for APLA. Moreover, APLAs such as lupus anticoagulant or anticardiolipin antibodies are found in approximately 14% of patients with recurrent venous thromboembolism.

Pathophysiology of Antiphospholipid Syndrome

While the mere presence of APLAs does not guarantee the development of APS, a strong correlation exists between APLAs and thrombotic events, including venous thrombosis, myocardial infarction, and ischemic stroke. The specific antibody profile, including antibody type, titer, and coexisting conditions, influences the risk of developing clinical APS. Triple positivity for lupus anticoagulant and high titers of anticardiolipin and anti-β2GPI antibodies indicates a high risk, whereas isolated or intermittent positivity or low titers suggest a lower risk.

Patients with SLE, cardiovascular risk factors, recurrent thrombosis despite anticoagulation, or a history of arterial thrombosis are also at elevated risk of recurrent thrombosis. APLAs are considered pathogenic, actively contributing to thrombosis, not merely serving as serological markers of APS, as shown in Figure 1.

Figure 1: Association between antiphospholipid antibodies (APLAs) and antiphospholipid syndrome (APS), illustrating the role of APLAs in abnormal blood clotting and thrombosis.

The “two-hit” thrombosis model explains thrombus formation in APS. The first “hit” involves endothelial injury, and the second “hit” amplifies thrombus formation. Beta-2-glycoprotein-I typically does not bind to unstimulated endothelium. One theory proposes that in cases of unidentified endothelial injury, redox imbalance within vascular beds could prime the endothelium. APS patients often have reduced levels of protective beta-2 glycoprotein-I. Annexin A2, an endothelial cell surface receptor, increases with oxidative stress. Factors like smoking can cause endothelial injury and increase thrombotic susceptibility in individuals with lupus anticoagulants.

Plasma nitrite levels are lower in APS patients compared to healthy individuals. Reduced endothelial nitric oxide synthase expression and activity lead to peroxynitrite and superoxide generation. Preclinical models demonstrate that domain I of beta-2 glycoprotein-I autoantibodies inhibits endothelial nitric oxide synthase, resulting in monocyte adhesion and reduced nitric oxide-dependent arterial relaxation.

APLAs enhance tissue factor expression through intracellular signaling pathways after binding anti-β2GPI autoantibodies on monocytes and endothelial cell multiprotein complexes. Autoantibodies from APS patients disrupt neutrophil and monocyte mitochondrial function, increasing reactive oxygen species production and subsequent tissue factor expression. Complement activation and fibrinolysis inhibition by APLAs are also established mechanisms.

In APS-related pregnancy loss, intraplacental thrombosis, complement pathway activation, interference with trophoblast growth and differentiation, impaired trophoblastic invasion, and hormonal effects are significant factors. A study of nearly 600 pregnant women with fetal loss after 20 weeks found that 9.6% were positive for at least one APLA.

Histopathology of Antiphospholipid Syndrome

Renal biopsies from APS patients with kidney involvement show thrombotic microangiopathy, characterized by fibrin thrombi in glomeruli or arterioles without inflammatory cells or immune complexes, fibrous intimal hyperplasia, and focal cortical atrophy. Thyroidization may be present and should be distinguished from lupus nephritis lesions.

Skin biopsies from non-healing ulcers are usually non-specific but may reveal small vessel and endothelial proliferation without significant vasculitis. Cardiac biopsies, if performed, might show small vessel thrombosis. Bronchiolar lavage can show hemosiderin-laden macrophages, while lung biopsies may indicate capillaritis or microthrombi.

History and Physical Examination in APS Diagnosis

Clinical presentations of APS vary widely, from asymptomatic APLA positivity to severe catastrophic APS. Vascular thrombosis and pregnancy-related complications are key features, but other organ systems can also be involved (non-criteria manifestations).

Vascular Thrombosis: APS can cause arterial or venous thrombosis in any organ, potentially recurrent and in unusual locations like upper extremity thrombosis, Budd-Chiari syndrome, and sagittal sinus thrombosis. DVTs are common venous events, potentially leading to pulmonary embolism and hypertension. Other venous sites include pelvic, renal, mesenteric, hepatic, portal, axillary, ocular, sagittal, and inferior vena cava.

Arterial thrombosis can affect arteries of any size. Transient ischemic events (TIEs) or ischemic stroke are common arterial manifestations. In young patients without atherosclerosis risk factors, TIEs or stroke should raise suspicion for APS. Other arterial sites include retinal, brachial, coronary, mesenteric, and peripheral arteries. Arterial thrombosis carries a poorer prognosis due to high recurrence risk.

Pregnancy Morbidity: Pregnancy loss is frequent in APS, especially in the second or third trimester. While genetic and chromosomal defects are common in early losses, fetal loss after 20 weeks is associated with about 10% APLA positivity. Triple positivity, prior pregnancy loss, thrombosis history, and SLE are risk factors for adverse pregnancy outcomes and losses in APS. Other complications include preeclampsia, fetal distress, premature birth, intrauterine growth retardation, placental insufficiency, placental abruption, and HELLP syndrome.

Cutaneous Involvement: Cutaneous manifestations, though non-specific, include livedo reticularis (most common, also seen in healthy individuals and other conditions), skin ulcerations (especially on lower extremities, resembling pyoderma gangrenosum), nail-fold infarcts, digital gangrene, superficial thrombophlebitis, and necrotizing purpura.

Valvular Involvement: Cardiac valve involvement is prevalent in APS, potentially as high as 80%. Mitral and aortic valves are most often affected, showing thickening, nodules, and vegetations on echocardiography, possibly leading to regurgitation or stenosis.

Hematological Involvement: Thrombocytopenia occurs in over 15% of APS cases, though severe hemorrhage is rare. A positive Coombs test is frequent, but hemolytic anemia is uncommon.

Neurological Involvement: Common neurological complications include TIEs and ischemic stroke, potentially recurrent, leading to cognitive dysfunction, seizures, and multi-infarct dementia. Blindness from retinal artery or vein occlusion and sudden deafness due to sensorineural hearing loss are also reported.

Cardiac Involvement: Myocardial infarction and cardiac emboli are possible. Non-ST segment elevation myocardial infarction with normal coronary angiography and abnormal cardiac MRI findings (transmural or subendocardial late gadolinium enhancement, T2 abnormalities, or perfusion abnormalities) suggests APS.

Pulmonary Involvement: Pulmonary artery thromboembolism from DVT is common, potentially causing pulmonary hypertension. Diffuse pulmonary hemorrhage from pulmonary capillaritis has also been reported.

Renal Involvement: Hypertension, proteinuria, and renal failure due to thrombotic microangiopathy are classic renal manifestations, though not specific. Renal artery thrombosis causing refractory hypertension and focal cortical atrophy are other reported renal issues.

Catastrophic Antiphospholipid Syndrome (CAPS): CAPS is a rare but life-threatening APS complication, affecting less than 1% of APS patients, with high mortality (48%). It involves thrombosis in multiple organs over a short period, often days, affecting small to medium arteries. Clinical presentations vary by organ, including peripheral thrombosis, pulmonary complications (ARDS, pulmonary embolism, hemorrhage), renal manifestations (thrombotic microangiopathy, renal failure), cutaneous symptoms (livedo reticularis, digital ischemia, gangrene, ulcers), cerebral manifestations (stroke, encephalopathy), cardiac complications (valve lesions, myocardial infarction, heart failure), hematological issues (thrombocytopenia), and gastrointestinal involvement (bowel infarction).

Common CAPS triggers include stopping anticoagulation in APS patients, infections, and surgical procedures. Prompt infection management and perioperative anticoagulation are recommended.

CAPS classification criteria (preliminary, 2003) include:

• Involvement of 3+ organs/systems/tissues.
• Manifestations developing simultaneously or within a week.
• Histopathological confirmation of small vessel occlusion in at least one organ.
• Laboratory confirmation of APLAs.

Definite CAPS requires all four criteria; probable CAPS is diagnosed with 3 criteria and incomplete fulfillment of the fourth.

Evaluation and Diagnosis of Antiphospholipid Syndrome

Diagnosis of antiphospholipid syndrome relies on both clinical and laboratory criteria. Clinical criteria involve vascular thrombosis or pregnancy morbidity, while laboratory criteria require the presence of lupus anticoagulant or moderate-to-high titers of IgG or IgM anticardiolipin or anti-β2GPI antibodies. Crucially, laboratory criteria necessitate a repeat positive APLA test at least 12 weeks after the initial positive result to exclude transient antibodies. A diagnosis of APS is questionable if the interval is less than 12 weeks or if more than 5 years separate clinical manifestations and positive laboratory tests. For detailed information, refer to StatPearls’ resource, “Antiphospholipid Antibody Testing.”

Lupus Anticoagulant Test: A positive lupus anticoagulant test strongly predicts adverse pregnancy events and is more specific, though less sensitive than anticardiolipin antibodies, for thrombosis prediction. About 20% of patients with anticardiolipin antibodies have a positive lupus anticoagulant test, while 80% with a positive lupus anticoagulant test also have anticardiolipin antibodies, as shown in Table 1.

Table 1: Effect of Lupus Anticoagulant and Anticoagulants on Laboratory Testing. This table details how lupus anticoagulant and common anticoagulants affect various coagulation tests, crucial for accurate diagnosis and monitoring.

A false-positive syphilis test does not fulfill APS diagnostic criteria, but APLA assessment is advised for patients with prior thrombotic or adverse pregnancy events. Lupus anticoagulant indicates an in vitro inhibitor of phospholipid-dependent coagulation reactions, not directly reacting with coagulation factors and not associated with bleeding risks. Heparin or warfarin can cause false-positive and false-negative results.

The lupus anticoagulant test involves four steps:

1. Initial screening: Prolonged phospholipid-dependent clot formation (e.g., activated partial thromboplastin time or dilute Russell viper venom time).
2. Mixing study: Prolonged screening test persists after mixing patient plasma with normal platelet-poor plasma, indicating no coagulation factor deficiency.
3. Phospholipid neutralization: Correction or improvement of prolonged screening test upon adding excess phospholipid, confirming phospholipid dependency.
4. Inhibitor exclusion: Ruling out other inhibitors.

Anticardiolipin and Anti-Beta-2-Glycoprotein-I Antibodies: These antibodies are assessed via ELISA, commonly testing for IgG and IgM isotypes. IgG antibodies correlate better with clinical manifestations than IgM or IgA. Titers over 40 IgG units are linked to thrombotic events, while lower titers have less established associations.

Other Laboratory Findings: Thrombocytopenia or anemia may be present in APS. Renal failure and proteinuria suggest renal involvement with thrombotic microangiopathy. Erythrocyte sedimentation rate might be elevated during acute thrombosis, but other inflammation markers are usually normal. SLE patients may have SLE-specific serologies (antinuclear, anti-double-stranded DNA, or anti-smith antibodies). Hypocomplementemia is atypical in APS and, with renal involvement, may suggest lupus nephritis.

Positive antinuclear and anti-double-stranded DNA antibodies can occur in primary APS without SLE and do not automatically indicate SLE without clinical lupus features. Patients with recurrent thrombosis or pregnancy losses should also be evaluated for other hypercoagulable states (hyperhomocysteinemia, factor V Leiden and prothrombin mutations, protein C, protein S, or antithrombin III deficiencies).

Classification Criteria: The revised Sapporo classification criteria (2006), updated from the initial 1999 criteria, require at least one clinical and one laboratory criterion for APS diagnosis.

Clinical Criteria:

• Vascular Thrombosis: One or more arterial, venous, or small-vessel thrombosis events in any organ, objectively confirmed by imaging or histopathology (thrombosis without significant vessel wall inflammation). Past thrombotic episodes are acceptable if confirmed and without other causes. Superficial venous thrombosis is not included.
• Pregnancy Morbidity:
  • One or more unexplained fetal deaths of normal fetuses at ≥10 weeks gestation.
  • One or more premature births of normal neonates before 34 weeks due to eclampsia, severe preeclampsia, or placental insufficiency.
  • Three or more consecutive spontaneous abortions before 10 weeks gestation, excluding anatomical, hormonal, or parental chromosomal causes.

Laboratory Criteria:

• Lupus anticoagulant detection in plasma on ≥2 occasions, ≥12 weeks apart.
• IgG or IgM anticardiolipin antibodies in serum/plasma at moderate-to-high titers (>40 GPL or GPM, or >99th percentile) by standard ELISA on ≥2 occasions, ≥12 weeks apart.
• IgG or IgM anti-β2GPI antibodies in serum/plasma at moderate-to-high titers (>99th percentile) by standard ELISA on ≥2 occasions, ≥12 weeks apart.

The 2023 ACR/EULAR APS classification criteria are more complex, introducing a weighted scoring system across clinical (macrovascular venous/arterial thromboembolism, microvascular, obstetric, cardiac valve, hematologic) and laboratory domains (lupus anticoagulant, IgG/IgM anticardiolipin or β2GP1b). Patients need ≥3 points in both clinical and laboratory domains for APS classification. These new criteria show higher specificity (99% vs. 86%) but lower sensitivity (84% vs. 99%) compared to the 2006 Sapporo criteria. Detailed criteria are available at DOI: 10.1002/art.42624.

Treatment and Management of Antiphospholipid Syndrome

Thrombosis Management: EULAR guidelines provide specific recommendations for various clinical scenarios. Primary thromboprophylaxis in APLA-positive patients without prior thrombotic events or pregnancy issues is debatable. APLA confirmation is needed ≥12 weeks post-initial testing. SLE patients with positive APLA are at higher thrombosis risk, and hydroxychloroquine is recommended for its thromboprotective effects. Low-dose aspirin may also be considered for high-risk APLA profiles (triple positivity, other thrombotic risk factors, no prior thrombotic events).

Primary Prevention: High-risk patients include those with positive lupus anticoagulant, 2 or 3 positive APLAs, or persistently high APLAs.

• High-risk APLA profile, no thrombotic events: Low-dose aspirin (75-100 mg).
• SLE patients, no thrombosis or pregnancy complications:
  • High-risk APLA profile: Prophylactic low-dose aspirin recommended.
  • Low-risk APLA profile: Prophylactic low-dose aspirin may be considered.
  • Nonpregnant women with obstetric APS only (with/without SLE): Prophylactic low-dose aspirin after risk/benefit assessment recommended.

Secondary Prevention:

• Arterial Thrombosis: Warfarin is generally preferred over DOACs. INR goal is typically 2.0-3.0, though some suggest >3.0.

  • LMWH for warfarin intolerance or non-response.
  • Recurrent thrombosis on warfarin: Add aspirin, switch to LMWH, or increase INR goal to >3.0. Check warfarin adherence and INR frequency.
  • DOACs may be considered for warfarin intolerance or INR target issues. Dabigatran may be more effective than other DOACs due to its anti-factor IIa mechanism.
  • Elderly stroke patients with low-titer anticardiolipin antibodies can be treated with low-dose aspirin, as low titers may be incidental.

• Lupus anticoagulant can falsely prolong APPT, PT, and INR. Consider prothrombin levels or factor X activity measurement if available.

• Triple Positivity: DOACs are generally not recommended for triple-positive APS patients or those with arterial thrombosis and APS. Warfarin is preferred due to DOACs showing inferior efficacy in trials and increased thrombotic events. Warfarin is recommended over DOACs for any APS patient with a thrombotic event (venous or arterial).

Pregnancy Management: Pregnant APLA-positive women need close monitoring for fetal well-being and maternal complications. Treatment aims to reduce adverse fetal outcomes. Warfarin is teratogenic and avoided in pregnancy. DOACs are also avoided due to safety data lacking. LMWH is preferred over unfractionated heparin due to better bioavailability, longer half-life, once-daily dosing, and lower thrombocytopenia and osteoporosis risks. EULAR recommendations for pregnant women:

• APLA-positive, no thrombosis history:
  • First pregnancy: No treatment.
  • Single pregnancy loss <10 weeks: No treatment.
  • High-risk APLA, no thrombosis/pregnancy complications: Consider low-dose aspirin.
• Delivery <34 weeks due to eclampsia/preeclampsia/placental insufficiency: Low-dose aspirin or low-dose aspirin + prophylactic heparin based on risk profile.
• Less defined criteria (2 miscarriages 34 weeks due to eclampsia/preeclampsia): Low-dose aspirin or prophylactic heparin based on risk profile.
• Definite obstetric APS with recurrent pregnancy complications despite low-dose aspirin + prophylactic heparin/LMWH: Consider increasing heparin to therapeutic dose or adding hydroxychloroquine/low-dose prednisolone in first trimester. IVIG may be considered in select cases when other treatments fail.
• Thrombotic APS history: Low-dose aspirin + therapeutic dose heparin during pregnancy recommended. Switch from warfarin to therapeutic heparin/LMWH upon pregnancy confirmation, ideally before week 6, due to warfarin teratogenicity.

Management of Other Manifestations: Anticoagulation role in non-criteria APS manifestations is not established. Thrombocytopenia with platelet count >50,000/mL3 needs no treatment; corticosteroids +/- IVIG or rituximab for <50,000/mL3. Splenectomy can benefit refractory thrombocytopenia. Renal thrombotic microangiopathy requires renal biopsy to exclude lupus nephritis (especially in SLE patients). Anticoagulation and corticosteroids can be used. Effective treatment for cardiac valve nodules/deformities is unknown; anticoagulation is recommended with embolism or intracardiac thrombus evidence.

Catastrophic Antiphospholipid Syndrome (CAPS) Management: Early CAPS diagnosis is crucial due to high mortality. Combination therapy with glucocorticoids, heparin, and plasma exchange or IVIG is first-line treatment, over single agents. Treat precipitating factors (infections, gangrene, malignancy). Refractory CAPS may require B-cell depletion (rituximab, cyclophosphamide) or complement inhibition (eculizumab), based on case reports.

Follow-up Monitoring: Stable anticoagulated patients without systemic autoimmune diseases need outpatient visits once or twice yearly. Coagulation studies before anticoagulation and during therapy guide dosing. Biochemistry panel (renal function) and complete blood count monitor patients. Repeated APLA testing is usually not indicated unless needed for future treatment decisions. Symptomatic organ involvement requires appropriate evaluations based on symptoms.

Differential Diagnosis of Antiphospholipid Syndrome

Thrombosis in antiphospholipid syndrome must be differentiated from other hypercoagulable conditions like hyperhomocysteinemia, factor V Leiden and prothrombin mutations, or protein C, protein S, or antithrombin III deficiencies.

APS-associated nephropathy needs differentiation from thrombotic thrombocytopenic purpura (TTP), vasculitis, hemolytic uremic syndrome, malignant hypertension, and lupus nephritis. Kidney biopsy is often needed for definitive diagnosis.

Prognosis of Antiphospholipid Syndrome

European studies report 90-94% 10-year survival in APS. However, morbidity remains high, with >30% developing permanent organ damage and >20% severe disability at 10-year follow-up. Poor prognostic factors include CAPS, pulmonary hypertension, nephropathy, CNS involvement, and extremity gangrene.

Prognosis is similar for primary and secondary APS, but secondary APS may have increased morbidity due to underlying rheumatic/autoimmune disorders. Lupus patients with APLAs have higher neuropsychiatric disorder risk. Elevated APLAs with malignancy are associated with poor prognosis, with or without thromboses.

Complications of Antiphospholipid Syndrome

Antiphospholipid syndrome can lead to complications in affected organs, including fetal loss, stroke, pulmonary embolism, pulmonary hypertension, valvular abnormalities, acute coronary syndrome, mesenteric thrombosis, or hepatic venoocclusive disease.

Perioperative complications are common in APS patients due to increased surgical prothrombotic risk. Preoperative anticoagulation strategy should be defined to prevent thrombosis.

Consultations for Antiphospholipid Syndrome

Patients with APS often require consultation with internists, rheumatologists, hematologists, and obstetricians.

Deterrence and Patient Education for APS

Patients should be educated about potential APS complications and symptoms requiring medical attention, such as TIA indicators. Clear communication about medication regimens and adherence is essential. Warfarin patients need frequent INR monitoring and dietary guidance to avoid warfarin interference.

Pearls and Other Issues in APS Management

Identifying and managing other prothrombotic risk factors (hyperlipidemia, smoking, hypertension, oral contraceptives) is crucial in APS patients.

Enhancing Healthcare Team Outcomes in APS

APS management requires an interprofessional team, with primary care physicians crucial for initial identification. Hematologists and rheumatologists are key for diagnosis, management, and follow-up. Neurology, nephrology, cardiology, and dermatology involvement may be needed for organ-specific issues. Anticoagulation clinics are vital for INR monitoring and warfarin management.

Given APS complexity and diverse underlying conditions, all team members must contribute to diagnosis and treatment, especially in pregnancy, requiring obstetrics and maternal-fetal medicine specialists. Pharmacists assist in drug interaction management, appropriate warfarin dosing, and INR monitoring. Specialty-trained nurses share this role. Open communication and close patient monitoring are vital for effective APS management.

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References

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