Heparin: Heparin works to inhibit the blood clotting reactions caused by thrombin and fibrin by
inactivating these proteins.
Warfarin: Warfarin functions as a vitamin K antagonist. Vitamin K functions to regulate the
production of the cofactors, and warfarin functions to prevent vitamin K from performing this
function.
Why do The prothrombin time (PT) is used, often along with a partial
thromboplastin time?
Prothrombin Time (PT) and Partial Thromboplastin Time (PTT) are commonly used coagulation
tests that provide valuable information about the functioning of different pathways within the
coagulation cascade. Healthcare providers often order these tests together or in conjunction for
several reasons:
Comprehensive Assessment of Coagulation Cascade:
The PT primarily assesses the extrinsic and common pathways of the coagulation cascade, while the
PTT focuses on the intrinsic and common pathways. By ordering both tests, healthcare professionals
can obtain a more comprehensive evaluation of the entire coagulation process.
Identification of Specific Coagulation Deficiencies:
Different clotting factors are involved in the intrinsic and extrinsic pathways. By combining PT and
PTT, healthcare providers can pinpoint specific deficiencies or abnormalities in the clotting factors,
helping to diagnose and differentiate between various bleeding disorders.
Monitoring Anticoagulant Therapy:
PT is used to monitor anticoagulant therapy, particularly with vitamin K antagonists such as
warfarin. The International Normalized Ratio (INR), derived from the PT, is used to standardize
results and facilitate consistent monitoring.
PTT is more sensitive to heparin, an anticoagulant used in different clinical settings. When
monitoring patients on heparin therapy, PTT is often used to assess therapeutic levels.
Screening for Coagulation Disorders:
PT and PTT are essential components of the coagulation profile, which is routinely used to screen for
coagulation disorders. These tests help identify abnormalities that may contribute to bleeding or
thrombotic tendencies.
Preoperative and Perioperative Assessment:
Prior to surgical procedures, healthcare providers may order PT and PTT to assess a patient's risk of
bleeding or clotting during and after surgery. This information helps guide decisions about
perioperative management, including the use of anticoagulant medications.
Evaluation of Liver Function:
Since many coagulation factors are produced in the liver, PT is often used as a marker of liver
function. Liver diseases that affect the synthesis of clotting factors can result in prolonged PT.
Hematologic Disorders:
PT and PTT are valuable in diagnosing and monitoring various hematologic disorders, including
hemophilia and von Willebrand disease.
In summary, the combination of PT and PTT allows healthcare providers to assess different aspects
of the coagulation cascade, identify specific coagulation factor deficiencies, monitor anticoagulant
therapy, screen for coagulation disorders, and evaluate the overall hemostatic balance. The
information obtained from these tests helps guide clinical decision-making, especially in the context
of bleeding or thrombotic disorders.
The PT test evaluates how well all of the coagulation factors in the extrinsic and common
pathways of the coagulation cascade work together. Included are: factors I (Fibrinogen), II
(Prothrombin), V, VII and X.
The PT/INR may be done at the same time as a PTT, which evaluates the clotting factors that are
part of the intrinsic and common pathways: XII, XI, IX, VIII, X, V, II (prothrombin), and I
(fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HK).
Precautions:
In the case of insufficient mixing a clot could be formed in the sample [3]. Underfilled tubes or
prolonged storage before testing may lead to a decrease of coagulation factor activities or altered
impression of the anticoagulant effect in a monitoring situation [4–7].
The recommended 3.2% (105– 109 mmol/L) citrate tubes are used