Different patterns of activated partial thromboplastin time (APTT) clot waveforms predicting the presence of lupus anticoagulant.

INTRODUCTION: Atypical peak pattern in second derivative curve of clot wave of Activated Partial Thromboplastin Time (APTT) was known to be associated with presence of Lupus Anticoagulant (LA), but clinical significance of other abnormal patterns was uncertain. METHOD: We retrospectively reviewed second derivative curves of clot waves of 271 samples with prolonged APTT (> 50 sec). These were approximated by fifth-order functions using polynomial regression analysis, and Principal Component Analysis (PCA) was performed to classify these functions. RESULTS: PCA analysis could separate a cluster of abnormal waveforms from that of normal pattern. Abnormal waveforms could be classified into atypical peak pattern, S-shaped pattern and Left Bundle Branch Block (LBBB)-like pattern, which formed discrete clusters on the PCA plot. While only a small proportion of cases with normal pattern were positive for LA (8/202 cases), all of these abnormal patterns were associated with LA (5/23, 9/27, 4/19 cases, respectively). DISCUSSION: Our analysis demonstrated that as well as atypical peak pattern, S-shaped and LBBB-like patterns could predict the presence of LA in cases with prolonged APTT.