Abstract: A thromboplastin extract including an aqueous thromboplastin extract of a powdered thromboplastin source including a metal ion chelator. A thromboplastin reagent for use in blood coagulation tests, the thromboplastin reagent includes the extract and calcium ions, and may include one or more of a stabilizer and a preservative.A process for preparing a thromboplastin extract including extracting a powdered thromboplastin source in an aqueous solution having a metal ion chelator, and separating the powder in solution into sedimented powder and supernatant thromboplastin extract. The supernatant thromboplastin extract is mixed with calcium ions, and may be mixed with one or more of a stabilizer and a preservative, to prepare thromboplastin reagent.