Purpose <p>Rapid coagulation function evaluation is critical in clinical diagnosis. Traditional coagulation analyzers cannot be well applied to point-of-care testing (POCT), because whole blood requires tedious preprocessing such as centrifugation. This work proposes a vertical transmittance turbidimetry method targeting whole blood direct coagulation measurement, so as to resolve the on-site testing bottlenecks of conventional devices.</p> Methods <p>A prototype integrated with a high-sensitivity photoelectric amplifier, PID thermostatic system and customized three-layer sandwich micro-reactor was constructed. Core detection is realized by capturing optical changes caused by the physiological characteristic of clot retraction during blood coagulation. Porcine whole blood was adopted for thrombin time (TT) measurement, and TT reagents were added to activate the coagulation process. Real-time transmittance signals were processed via high-order polynomial fitting, and TT values were determined from the inflection points of transmittance derivative curves.</p> Results <p>Optoelectronic characterization verifies excellent system stability with RSD &lt; 3% and high linearity of <i>R</i>² = 0.9999. The average measured TT of porcine blood is 61.08&#xa0;s, with a coefficient of variation (CV) of 9.06%, which far outperforms the industrial standard limit of 15%.</p> Conclusion <p>Centrifugation pretreatment is completely eliminated in the proposed system. Featuring compact layout and high testing precision, the vertical transmittance turbidimetry technique based on clot retraction provides a cost-effective solution for direct whole-blood POCT coagulation detection.</p>