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Antiphospholipid syndrome


Antiphospholipid syndrome



§   Although the phospholipid surface used in most in vitro coagulation assays favors inhibition of procoagulant pathways and therefore prolongation of clotting, the microenvironment of cell membranes in vivo may promote greater inhibition of anticoagulant pathways and therefore thrombosis


Procoagulant effects

§   Inhibition of the activated protein C pathway

§   Inhibition of antithrombin III activity

§   Inhibition of anticoagulant activity of b2-glycoprotein I

§   Inhibition of fibrinolysis

§   Disruption of annexin V shield on membranes

§   Up-regulation of the tissue factor pathway

§   Enhanced binding to membranes of b2-glycoprotein I and prothrombin

§   Activation of:

1.      endothelial cells

2.      leukocytes to endothelial cells

3.      neutrophils including degranulation

4.      platelet activation / aggregation


Anticoagulant effects

§   Inhibition of activation of factor II, IX and X

§   (the steps in the pathways dependent on phospholipid)


Clinical features

§   Venous thrombosis, especially deep venous thrombosis of the legs, is the most common manifestation (29-55%) – up to half of these also have PEs

§   Arterial thrombosis

1.      CVA / TIA (50%)

2.      MI (23%)

3.      Subclavian, renal, retinal, and pedal arteries (remainder)

§   Cardiac valvular abnormalities (up to 63%) and marantic endocarditis

§   Levido reticularis

§   Thrombocytopenia

§   Miscarriage

§        Also pre-eclampsia and placental insufficiency

§        Best tested preconceptually as antibodies may be down regulated during pregnancy

§        Some women with aPLs have anti-Ro

§        2% risk of fetal heart block


Sneddon’s syndrome may represent undiagnosed antiphospholipid syndrome - clinical triad of:

1.      stroke

2.      livedo reticularis

3.      hypertension


Prevalence of 1 to 5 percent for both anticardiolipin antibodies and lupus anticoagulant antibodies in young healthy controls

Also found in:

§   infections

§   cancer

§   drugs

§   hemodialysis

Usually IgM antibodies that are present at low levels and not associated with thrombotic events



SLE – secondary antiphospholipid syndrome

§   12-30% have antiphospholipid antibodies

§   50 to 70 percent of patients with both SLE and antiphospholipid antibodies develop antiphospholipid syndrome after 20 years of follow-up.

§   Can also be secondary to other AI disorders:

§   Rheumatoid arthritis

§   Systemic sclerosis

§   Bechets/ temporal arteritis/ sjogrens


Differential diagnosis of arterial and venous thrombosis

§   Defects in clot lysis (Dysfibrinogenemia*, Deficiency of plasminogen-activator inhibitor type 1)

§   Metabolic (Homocysteinemia)

§   Platelet disorders (HIT, Myeloproliferative disorders, PNH, Polycythemia vera (with thrombocytosis))

§   Hyperviscosity (Polycythemia vera, Waldenström’s macroglobulinemia, Sickle cell anemia, Acute leukemia)



Diagnostic criteria


Clinical criteria (Sapporo criteria 1999 – updated in 2006)

Vascular thrombosis

§   One or more clinical episodes of arterial, venous, or small-vessel thrombosis, occurring within any tissue or organ

Complications of pregnancy

§   One or more unexplained deaths of morphologically normal fetus at or after the 10th week of gestation.

§   One or more premature births of morphologically normal neonates at or before the 34th week of gestation.

§   Three or more unexplained consecutive spontaneous abortions before the 10th week of gestation


Laboratory criteria

§   Anticardiolipin IgG or IgM antibodies present at moderate or high levels in the blood on two or more occasions at least twelve weeks apart

§   Lupus anticoagulant antibodies detected in the blood on two or more occasions at least twelve weeks apart, according to the guidelines of the International Society on Thrombosis and Haemostasis

§   Now anti-beta2 glycoprotein 1 antibodies added



Methods of detection


Testing should be restricted to those with a history of thrombotic events / SLE / pregnancy complications

LAs are a stronger RF than aCLs for thrombosis


Lupus anticoagulant antibodies

§   Lupus anticoagulants are APAs that interfere with phospholipid-dependant stage of coagulation

§   Stronger association with thrombosis than anticardiolipin antibodies

The first step is prolongation of coagulation in at least one phospholipid-dependent in vitro coagulation assay with the use of platelet-poor plasma.

§   Sensitive to eliminate false negatives

§   More than one test should be used

§   Plasma needs to be as free as platelets as possible

§   Double centrifugation

§   Filtering

§   Effects of repeated thawing

§   Platelet free normal pooled control

These assays can be subdivided according to the portion of the coagulation cascade that they evaluate as follows:

1.      The extrinsic coagulation pathway (dilute prothrombin time)

2.      The intrinsic coagulation pathway (activated partial-thromboplastin time, dilute activated partial-thromboplastin time, colloidal-silica clotting time, and kaolin clotting time)

a.      APTT

i.   Sensitivity is determined by the phospholipids in the reagent

ii. Acute phase and pregnancy increase factor 8 and fibrinogen and may shorten the APTT masking a weak inhibitor

b.      KCT

i.   No additional phospholipids added, relies on plasma lipid and residual cell membrane fragments

ii. Very sensitive, but also very vulnerable to platelet contamination

3.      The final common coagulation pathway (dilute Russell’s viper-venom time, Taipan venom time, and Textarin and Ecarin times).§

a.      Taipan and textarin are relatively insensitive to prothrombin deficiency and therefore can be used in patients on warfarin

b.      Textarin/ ecarin time

i.   With LA – textarin is prolonged, ecarin normal

ii. High textarin: ecarin ratio

c.      Textarin requires Factor V, taipan doesn’t.

d.      Some DRVVT reagents contain heparin neutralizers and can be used for patients on therapeutic heparin


The second step is a failure to correct the prolonged coagulation time by mixing the patient’s plasma with normal plasma.

§   If weak, mixing may dilute the inhibitor giving false negative results


The third step is confirmation of the presence of lupus anticoagulant antibodies by shortening or correction of the prolonged coagulation time after the addition of excess phospholipid or platelets that have been frozen and then thawed. (exposes procoagulant phospholipids)

§   Platelet neutralization procedure

§   NEQAS suggest that some misdiagnoses are due to incomplete neutralization.


The fourth step is ruling out other coagulopathies with the use of specific factor assays if the confirmatory test is negative or if a specific factor inhibitor is suspected.


Neat plasma

50:50 mix



PL correction


PL correction






No LA detected





LA detected





LA detected but diluted in 50:50





Factor deficiency





LA and factor deficiency





Other inhibitor / heparin



Anticardiolipin antibodies

ACAs require b2-GP1 as a co-factor for binding to phospholipid

Solid-phase immunoassay (usually enzyme-linked immunosorbent assay) is performed on cardiolipin-coated plates, usually in the presence of bovine serum b2-glycoprotein I. Anticardiolipin antibodies from patients with the antiphospholipid syndrome are b2-glycoprotein I–dependent; antibodies from patients with infectious diseases are b2-glycoprotein I–independent.¶


Anti–b2 glycoprotein I antibodies

§   Major antigen recognized by antiphospholipid autoantibodies

§   AKA apolipoprotein H

§   Associated with increased thrombotic risk

Solid-phase immunoassay (usually enzyme-linked immunosorbent assay) is performed on human b2-glycoprotein I–coated plates (usually g-irradiated polystyrene).¿ Anti–b2-glycoprotein I antibody assays detect antibodies to human b2-glycoprotein I, rather than bovine b2-glycoprotein I (as in anticardiolipin antibody assays).



§        Initial VTE with confirmed APLS

§        Probably 6 months treatment with an INR 2.5 with risk factor modification (e.g. avoidance of combined OCP or HRT)

§        Lifelong if recurrence

§        Retrospective study showed a 70% recurrence rate on discontinuation v. 90% thrombosis free over 5 years

§        Recuurence whilst on standard treatment

§        Higher INR 3-4

§        Catastrophic APLS

§        May also require plasmapheresis or immunosuppressive therapy

§        Arterial

§        Not completely clear

§        Most of the trials haven’t specifically addressed this

§        INR 3-4 probably better if bleeding risk acceptable

§        Controversy with CVD

§        BSH – recommends standard warfarin

§        Some evidence that aspirin alone superior

§        APASS and WARSS – no difference between aspirin and WARSS

§        Pregnancy

§        Limited evidence

§        Accepted practice

§        LMWH (prophylactic) and aspirin

§        Aspirin can be started preconceptually or as soon as pregnancy test positive

§        LMWH started when fetal heart beat detectable on US

§        For women with no history of thrombosis in whom early pregnancy loss is a feature, may be OK to stop LMWH at 34 weeks

§        Otherwise  continue to delivery +/- switch to UFH

§        Postpartum thromboprophylaxis


Key papers

Hughes et al., 1995

High intensity warfarin was more effective (retrospective study) than low intensity.

Crowther et al., 2003

High intensity warfarin therapy is not superior to low intensity, but 70% of the patients had venous thromboembolism