Antiphospholipid Antibody Syndrome

ANTIPHOSPHOLIPID ANTIBODY SYNDROME

ANTIPHOSPHOLIPID ANTIBODIES (APLA)-DEFINITIONS AND HISTORY

APLA are antibodies directed against certain phospholipids. There are found in variety of clinical situations. APLA are important to detect because in certain patients they are associated with a syndrome that includes a hypercoagulable state, thrombocytopenia, fetal loss, dementia, strokes, optic changes, Addison's disease, and skin rashes. APLA were first described by Conley in the 1950's when it was noted that patients with lupus often had prolonged activated partial thromboplastin times (APTT). Soon there after the associated with false positive VDRLs was noted. Despite the elevation of the aPTT it observed that these patients did not develop hemorrhagic complications unless they also had hypoprothrombinemia or thrombocytopenia. Bowie first described the association of APLA and thrombosis in 1964. Feinstein and Rapaport in an 1972 review called this phenomenon the "lupus anticoagulant". Harris, recognizing that cardiolipin is a major component of the VDRL test, developed and popularized the anticardiolipin (ACLA) antibody test in the mid-1980's. In the 1980's it become well recognized that patients did not have to have SLE to have symptomatic disease from APLA.

One major difficulty in studying APLA is that no one really knows what the underlying pathogenic mechanism is that leads to the clinical syndrome. This review will side-step this issue (best reviewed in the McNeil paper) and concentrate on clinical matters.

WHO GETS APLA?

About 30-50% of patients with SLE will have APLA. These antibodies can also be found in patients with other autoimmune diseases. Patients without lupus or other autoimmune disease can have symptomatic APLA ("Primary APLA syndrome"). Children will often develop transient APLA after viral infections. These often come to clinical attention during pre-operative evaluation for tonsillectomy. Up to 30% of patients with HIV infection will also develop APLA. The infection associated APLA are not associated with thrombosis. Medication may also induce APLA. Chlorpromazine is the most common but APLA have also been associated with procainamide, dilantin and quinidine. In screening studies of blood donors, up to 8% of normal people will have APLA. However the APLA in these people are usually low titer and most often occur in young women.

TESTS FOR ANTIPHOSPHOLIPID ANTIBODIES (APLA)

There are two main groups of tests for APLA's: testing for presence of antibodies to cardiolipin and the coagulation based tests for APLA.

Coagulation Based Tests: As you recall, APLA react with phospholipid. Phospholipids are used in coagulation tests to provide a surface for the coagulation reaction to occur. The basis for all these tests is that if there are antibodies binding to the phospholipid, it will interfere with the coagulation reaction and prolong the clotting time. Once an elevated aPTT is found one must verify it is due to an inhibitor by demonstrating it does not correct with a 50:50 mix. This is done by making a mixture of the patient's and normal pool plasma and performing a aPTT on it. Then the mixture is incubated for 30, 60 and 120 minutes and aPTT's are performed at various times. Each of the three major diagnostic considerations will perform differently on the 50:50 mix:

1. Factor Deficiency. aPTT will correct to normal at time 0 and stay in the normal range on each of the time points.

2. APLA. Does not correct to normal (may partially correct) at time 0 or any time point. May actually prolong further. (Lupus cofactor effect).

3. Factor Inhibitors. Corrects to normal at time 0 but then prolongs at next time points.

TIME (SECONDS) 0 30 60 120

NORMAL POOL 30 32 33 34

PATIENT'S 50 52 55 53

50:50-DEF(1) 30 32 33 34

50:50-APLA(2) 40 38 42 39

50:50-INHIB(3) 30 34 40 55

After one demonstrates the prolongation of the clotting time and establishes this is do to an inhibitor, then one needs to show its dependance on phospholipids. To do this one adds phospholipid derived from platelets or "hexagonal phase" phospholipids (named for the shape they assume in suspension). APLA bind avidly to both platelet and hexagonal phase" phospholipids. Thus addition of these lipids will correct the prolonged coagulation tests. Factor inhibitors will not correct with platelet phospholipids. To summarize, one screens for APLA with coagulation based tests to see if any test is prolonged. If one test is prolonged, then one uses a 50:50 mix to prove it an inhibitor. Then one uses platelet or hexagonal phospholipids to correct the abnormal clotting time.

aPTT. Only sensitive to 30% of APLA. One can increase sensitivity by using different reagents. Many patients with APLA will have normal aPTT and therefor one cannot exclude APLA by just doing a aPTT.

Dilute Russell Viper Venom Time (dRVVT). This test is very sensitive to any interference with phospholipid because it utilizes very little added phospholipid. It is performed by initiating the coagulation cascade with Russell Viper venom.

Kaolin clotting time. This test uses no added phospholipid and is the most sensitive test to APLA but is very technique demanding.

Platelet Neutralization Test. This test takes a reaction that is prolonged by plasma which does not correct with a 50:50 mix and adds extracts of platelet. If it corrects to normal this is very specific for APLA.

Hexagonal Phase Phospholipid. Same principles as the platelet neutralization test but used hexagonal phase phospholipids. Currently OHSU uses a testing system that corrects for anticoagulation and other factor deficiencies. Thus this is the only valid test for lupus inhibitors when patients are on anticoagulants.

Anticardiolipin Antibodies: This is an ELISA test for antibodies to cardiolipin. Therefore, unlike the coagulation based tests, it can be performed on plasma which has been anticoagulated. Tests results at OHSU is reported in standard deviation with >3SD abnormal. Tests are also reported as specific isotype (IgG, IgA, IgM). It is still debatable if specific isotypes are associated with different patterns of disease. The antibodies that react with cardiolipin are different ones then those which cause the lupus inhibitor effect. Only 60% of patients with APLA will have both ACLA and lupus inhibitors. Consequently one needs to assay for both in assessing patients for APLA. Recently is has been discovered that the ACLA actually react with a complex of a cardiolipin and protein known as beta-2-glycoprotein. ACLA tests utilizing this complex are being tested to see if they provide more clinical information then the routine APLA.