External Multicenter Validation of the APTTO Model for Prolonged APTT Using Clot Waveform Analysis

Inclusion Criteria: 1. Patients of any age (pediatric and adult populations) undergoing coagulation testing with: \- Prolonged activated partial thromboplastin time (APTT), defined as an APTT ratio ≥ 1.25. \- Normal prothrombin time (PT), according to local laboratory reference ranges. 2. Availability of clot waveform analysis (CWA) data obtained during routine APTT testing using: * Optical coagulation analyzers (ACL TOP platform). * Silica-based APTT reagent (SynthASil®). 3. Completion of the standard laboratory evaluation for prolonged APTT as part of routine clinical care, when clinically indicated. 4. Samples collected and processed in accordance with the standardized preanalytical protocol defined in the study SOP. 5. Patients evaluated in either: * Preoperative assessment, or * Routine clinical practice (non-preoperative setting). Exclusion Criteria: 1. Prolonged prothrombin time (PT) or combined prolongation of PT and APTT. 2- Inadequate preanalytical conditions, defined as non-compliance with the study SOP, including but not limited to: * Incorrect blood-to-anticoagulant ratio. * Delayed plasma processing beyond protocol-defined time limits. * Inadequate centrifugation or plasma quality. 3\. Absence of required CWA data or unavailable clot waveform images. 4\. Samples in which APTT values are outside the measurable range of the analyzer, preventing extraction of CWA-derived parameters. 5- Patients with missing essential clinical or laboratory data required for application of the APTTO models.