March 2025 Quick Question: LAC Testing Outcome

Our March 2025 Quick Question asked, “How do you test for lupus anticoagulant?” The question drew 38 responses.

1. DRVVT Screen/Confirm only: 4 (11%)
2. PTT Screen/Confirm only: 2 (5%)
3. First DRVVT S/C then PTT S/C if pos: 1 (3%)
4. First PTT S/C then DRVVT S/C if pos: 3 (7%)
5. Both DRVVT S/C & PTT S/C: 27 (71%)
6. We don’t test for LAC: 1 (3%)

Fully 71% of respondents understood the point of our question–the PTT– and DRVVT-based assays are not confirmatory. “Lupus anticoagulant” is a collective term for a family of phospholipid-binding autoantibodies with variant specificities. The LAC profile requires that we use at least two assays, PTT and DRVVT being the most prevalent for their sensitivities, although legacy assays such as the dilute prothrombin time (DPT), kaolin clotting time (KCT), and the tissue thromboplastin inhibition (TTI) test remain available. The latest ISTH guidelines for all antiphospholipid syndrome-related antibodies are available from your library: Devreese KMJ, Bertolaccini ML, Branch DW, et al. An update on laboratory detection and interpretation of antiphospholipid antibodies for diagnosis of antiphospholipid syndrome: guidance from the ISTH-SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies. J Thromb Haemost. 2025;23(2):731-744. doi: 10.1016/j.jtha.2024.10.022.

By the way, it is safe to assume that, while only one respondent chose answer 6, “We don’t test for LAC,” most of us who don’t perform LAC profile testing simply chose not to answer. Many acute care facilities prefer to send out LAC profiles to experienced reference facilities as the profiles demand both technical and interpretive expertise.

As always, we invite your comments on LAC testing, antiphospholipid syndrome, or any related topic.