Prolonged activated partial thromboplastin time (APTT) is a frequent laboratory finding that may reflect a broad spectrum of underlying conditions, ranging from benign laboratory abnormalities to clinically relevant hemostatic disorders. Clot waveform analysis (CWA), automatically generated during routine APTT testing by optical coagulation analyzers, provides additional quantitative and qualitative information on clot formation dynamics.
The APTTO model is a previously developed two-step predictive algorithm based on CWA features designed to estimate the probability of a pathological cause of prolonged APTT and to differentiate lupus anticoagulant from intrinsic pathway factor deficiency or von Willebrand disease. Internal validation has demonstrated good discrimination and calibration.
This multicenter observational study aims to perform an external validation of the APTTO model in independent patient cohorts, assessing its discrimination, calibration, and decision-analytic performance without model updating.
Optical coagulation analyzers (ACL TOP platform).
Silica-based APTT reagent (SynthASil®).
Completion of the standard laboratory evaluation for prolonged APTT as part of routine clinical care, when clinically indicated.
Samples collected and processed in accordance with the standardized preanalytical protocol defined in the study SOP.
Prolonged prothrombin time (PT) or combined prolongation of PT and APTT.
Incorrect blood-to-anticoagulant ratio.
Delayed plasma processing beyond protocol-defined time limits.
Inadequate centrifugation or plasma quality.