A blood test measuring clotting time via the intrinsic pathway, normally 25-35 seconds. It monitors heparin therapy and screens for clotting factor deficiencies like hemophilia.
Named for thromboplastin, a tissue extract that initiates clotting, with 'partial' indicating incomplete thromboplastin (lacking tissue factor). Developed in the 1950s to complement prothrombin time testing.
The PTT tests a completely different clotting pathway than PT - it's like having two separate emergency response systems for bleeding! Hemophiliacs have normal PT but prolonged PTT, showing how specific these pathways are.
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