in vitro Partial Thromboplastin Time (PTT)
The determination of the partial thromboplastin time (PTT) indicates delays in the coagulation time of recalcified plasma treated with a medical device. The coagulation time is described in seconds.
In the partial thromboplastin time assay phospholipids (e.g. cephalin) are used as main reagent and activating substances such as kaolin or celite to trigger coagulation. the phospholipids replace the platelet factor-3 and reduce the coagulation period of human or animal plasma in the presence of a defined calcium ion concentration.
For the in vitro testing of thrombogenic properties of medical devices the test is used without the activating reagent as the medical device is tested for its ability to act as the coagulation activating component.2
The PTT tests are performed in accordance with the ISO guidelines 10993-13, 10993-41 and 10993-124 or ASTM F2382 – 182 and ASTM F619-205 at Eurofins BioPharma Product Testing Munich GmbH.
Procedure
Plasma is gained from citrated fresh whole blood samples or fresh frozen plasma (FFP) is used. The plasma is incubated with the test item. The coagulation ability is re-established by the addition of calcium and the time until clot-formation occures is measured. Thrombogenic properties of the test material lead to shorter PTT, while anticoagulants like heparin lead to prolonged PTT.1,2
ISO vs. ASTM testing
References
- ISO 10993-4: “Selection of tests for interactions with blood”
- ASTM F2382 – 18: “Standard Test Method for Assessment of Circulating Blood-Contacting Medical Device Materials on Partial Thromboplastin Time (PTT)”
- ISO 10993-1: “Evaluation and testing within a risk management process”
- ISO 10993-12: “Sample preparation and reference materials”
- ASTM F 619 – 20: “Standard Practice for Extraction of Materials used in Medical Devices”
- Winter WE, Flax SD, Harris NS. Coagulation Testing in the Core Laboratory. Lab Med. 2017 Nov 8;48(4):295-313. doi: 10.1093/labmed/lmx050.
