Many of the LA recognize the hexagonal phase phospholipid configuration as an antigenic epitope and will be neutralized in contrast to factor-specific antibodies, which are not neutralized. The test is a two-part test:
- An aPTT-based assay is performed using an LA-sensitive reagent with and without the phospholipid source of hexagonal phase phosphatidyl-ethanolamine (HPE). The HPE neutralizes the LA in the patient's plasma, which results in a shortened time.
- An aPTT-based clotting time without the addition of the HPE. The result is considered positive when there is a difference of >8 seconds.
This test also includes the addition of normal plasma to correct for any prolongation of a clotting time due to a factor deficiency, increasing the test's specificity. The test includes a heparin neutralizer which makes the test insensitive to heparin levels up to 1 IU/mL. Direct thrombin inhibitors and FVIII inhibitors can cause false positives in this test.
