Measures of Coagulation
last authored: Feb 2010, David LaPierre
last reviewed:
Introduction
Coagulation, an integral part of hemostais, is a complex function depending on multiple things.
Platelet Counts
Platelet counts are usually done using an automated counter using anticoagulated blood. Readings well outside the reference range - 130 to 300 x 109/L - need to be verified manually to ensure artifactual clumping hasn't occurred.
Pseudo-thrombocytopenia can be mimicked by clumping, usually due to EDTA. A manual differential and count may be useful, as can using citrate as an anticoagulant.
increased
- reactive: bleeding, iron deficiency, infection, neoplasm
- primary myeloproliferative disorder
decreased
- pseudothrombocytopenia
- destruction (immune, other)
- marrow failure
- sequestration
INR
Partial Thromboplastin Time (PTT)
Partial Thromboplastim Time is a measure of intrinsic and common clotting pathways. Plasma clotting after addition of kaolin, cephalin, and calcium ions is measured in seconds.
Prolonged PTT can be due to problems with factor V, VIII, IX, X, XI, or XII, prothrombin, or fibrinogen.
Prothrombin Time (PT)
Prothrombin time measures the extrinsic and common coagulation pathways. Clotting of plasma is induced by addition of tissue thromboplastin and calcium ions, and is measured in seconds.
Prolonged PT can result from deficiency/dysfunction of factor V, factor VII, factor X, prothrombin, or fibrinogen. PT is also used as a test of liver function
Dade PTT
Bleeding Time
Bleeding time measures the time taken for a standardized skin puncture to stop bleeding. It assesses platelet response to limited vascular injury. The reference depends on the specific test and varies from 2-9 minutes.
Resources and References
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