Lupus anticoagulant is measured indirectly as an activity that prolongs the phospholipid-dependent clotting reaction. Its presence
should be suspected when the activated partial thromboplastin
time (APTT) is prolonged in the absence of a history of bleeding (1).
CRITERIA FOR DIAGNOSIS OF LUPUS ANTICOAGULANT
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- Prolongation of the activated
partial thromboplastin time (APTT). This occurs
as a result of antibodies binding to the in vitro phospholipid
which is necessary for the intrinsic pathway of the coagulation cascade.
Occasionally the prothrombin time (PT) is also
prolonged due a similar effect on the phospholipid
of the extrinsic pathway.
- Prolongation of APTT should
persist after the addition of an equal volume of normal plasma (this
excludes coagulation factor deficiencies).
- APTT should shorten by
increasing the phospholipid concentration in the
APTT reagent (inhibitory activity is directed at the phospholipids and not
to other specific coagulation proteins (2).
70 % of patients with lupus anticoagulant have anticardiolipin
antibodies, however the reverse is seldom true (2).
- Sait
KH, Van den Hof MC, Robinson KS. Antiphospholipid antibody syndrome in pregnancy. J
SOGC 1997; :1083-1092.
- Triplett DA. Antiphospholipid antibodies and recurrent pregnancy
loss. Am J Reprod Immunol
1989;20:52-67.