Further evaluation for the presence of Lupus Anticoagulant is indicated by a prolongation of a phospholipid-dependent test. A reagent's ability to manifest LA depends on its sensitivity, which is based on the phospholipid concentration. The aPTT reagents have varying sensitivities due to commercial preparation as well as the type and concentration of phospholipids. An aPTT is considered sensitive to lupus if it has a decreased phospholipid concentration. It allows the LA to be manifested as a prolonged aPTT. While an insensitive reagent has a high concentration of phosphatidyl serine which will mask the LA effect on the aPTT, resulting in a normal result. Many laboratories use an insensitive LA reagent to eliminate investigating a prolonged aPTT since these patients do not bleed.
Laboratories can also use two reagents to screen for LA testing. A sensitive reagent will present with a prolonged aPTT. Repeating the aPTT with an insensitive reagent with a high phospholipid concentration will overwhelm the antibody and normalize the aPTT result.
