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136 Antiphospholipid Antibodies■Three to five percent of the general population has antiphospholipid
antibodies.
■Antiphospholipid antibody syndrome (APS) is the presence of:
venous or arterial thrombosis or pregnancy morbidity (miscarriages,
severe pre-eclampsia; pre-term birth due to placental insufficiency),
in the setting of either the lupus anticoagulant or moderate to high
titer IgG or IgM anticardiolipin or anti-beta2 glycoprotein I.
■APS should be considered in young people with deep venous throm-
bosis or stroke.
■Cutaneous manifestations of APS include livedo reticularis, superfi-
cial thrombophlebitis, splinter hemorrhages, and leg ulcers.
■Non-thrombotic manifestations of antiphospholipid antibodies
include transverse myelitis and chorea.
tests
Basic Blood Studies
■Lupus anticoagulant (LA) is a clotting assay performed on plasma.
➣A PTT can miss 50% of lupus anticoagulants.
➣More sensitive screening tests are the modified Russell viper
venom time and sensitive PTT.
➣Once a prolonged clotting time is ascertained, two other steps
are necessary to confirm a LA: lack of correction with a mixing
study and demonstration of phospholipid dependence (such as
a platelet neutralization procedure).
■Anticardiolipin and anti-beta2 glycoprotein I are ELISA assays.
➣IgG is the isotype most closely associated with risk of thrombosis
and pregnancy loss.
➣24% of patients with APS are thrombocytopenic.
Specific Diagnostic Tests
■Fifty percent of patients with APS have SLE (“secondary” APS).
■Helpful serologic tests for SLE include ANA, anti-DNA, anti-RNP,
anti-Sm, anti-Ro, anti-La, C3, and C4.
Other Tests as Appropriate
■Imaging studies to diagnose thrombosis: brain MRI, brain CT, arte-
riogram, biopsy, and EKG.
■One-third of patients with APS may have heart valve vegetations or
thickened valves on transesophageal echo (TEE).
differential diagnosis
■Genetic causes of hypercoagulability: Factor V Leiden, prothrombin
mutation, Protein C deficiency, Protein S deficiency, anti-thrombin
III deficiency, homocysteinemia