General Approach of Haemostasis. Lupus Anticoagulant. Islamic University of Gaza. Anti- Phospholipids antibodies.
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The term "anticoagulant" accurately describes its function in vitro, but in vivo, it is now known that it functions as a coagulant
The ISTH recommends that the laboratory diagnosis of lupus anticoagulants (LA) should be carried out on double-centrifuged plasma following a four-step procedure adhering to these principles:
Intrinsic (aPTT, dilute aPTT, KCT, colloidal silica clotting time),
Final common pathway (dRVVT, Taipan venom time, Textarin and Ecarin time)
Correction of the prolonged coagulation time after addition of excess phospholipid or platelets
Lack of specific inhibition of one coagulation factor (such as FVIII:C,FIX:C, or FXI).
KCT is similar to APTT, the difference being that KCT reagent is devoid of phospholipids and incorporates Kaolin as contact activator. The test is performed on a range of mixture of normal and patient’s plasma. Different patterns of response are obtained indicating the presence of Lupus anticoagulants or the deficiency of one or more coagulation factors.
The KCT test though sensitive is not specific for LA, additionally:
Due to limited stability the platelet preparations loose their activities on storage hence do not show reproducible results.
Comment Specimen collection, centrifugation, and processing are critical when testing for the presence of an LA.
In patients with LA, autoantibodies bind the epitopes of reagent phospholipids thereby preventing the activation of prothrombinase complex. This results in a prolongation of clotting time with SCREENING reagent.
the D-dimer assay depends on the binding of a monoclonal antibody to a particular epitope on the D-dimer fragment.