Laboratory Identification of Lupus Anticoagulant (LA) Using Different Activated Partial Thromboplastin Time (APTT) Assays.

INTRODUCTION: The International Society of Thrombosis and Hemostasis (ISTH) guidelines suggest a three-step evaluation for the detection of lupus anticoagulant (LA), including screening, mixing, and confirmation. According to the guidelines, the LA assay based on activated partial thromboplastin time (APTT) should include an initial screening step followed by a confirmatory step that uses a higher concentration of phospholipids in either bilayer or hexagonal form. For the activator, the guidelines recommend using silica, though ellagic acid is also an option. In this context, HemosIL Silica Clotting Time (SCT, Instrumentation Laboratory) is the only assay that fully complies with the guidelines. However, there are other assays available using different reagents, such as Dade Actin FSL/FS (Siemens Healthcare Diagnostics) and PTT-LA/Staclot LA (Diagnostica Stago), and the relevance of these differences in LA detection is not known.

METHODS: This study compared the performance of the three platforms.

RESULTS: Out of 136 samples, the majority were from females (82%) with a median age of 41 years (IQR 32-50); 44 (32%) had a history of thrombosis, and 28 (21%) were on anticoagulants. PTT-LA/Staclot LA had the highest sensitivity (100%) and specificity (100%). There was an almost perfect agreement between PTT-LA/Staclot LA and Dade Actin FSL/FS (kappa 0.812). HemosIL SCT sensitivity was 100% and the specificity was 74%, which was increased to 99% by increasing the phospholipid concentration of the screening step.

CONCLUSION: We observed a good agreement between PTT-LA/Staclot LA and Dade Actin FSL/FS, and fair to moderate agreement with HemosIL SCT, whose performance improved with increasing phospholipid concentration. These results demonstrate that all three assays are comparable for APTT-LA detection.