Prothrombin Time With INR, Sodium Citrate Whole Blood

The prothrombin time is usually done when there are bleeding manifestations or symptoms of inappropriate blood clots. The prothrombin time (PT) measures the extrinsic pathway of coagulation. Prothrombin time along with activated partial thromboplastin time (aPTT) helps to diagnose the cause of bleeding or inappropriate blood clots. Coagulation factors are proteins which are involved in hemostasis (i.e helps to stop bleeding by forming blood clot, whenever there is injury). As soon as there is injury in the body and it bleeds, the coagulation factors get activated in an order and helps in forming a stable clot which stops the bleeding. This process occurs naturally in the body. If there is deficiency or insufficient quantity of any of the coagulation factor, the natural hemostasis is disturbed. If there is less or no coagulation factor it results in excess bleeding and if there is too much it leads to excess clotting. The international normalized ratio (INR) is calculated from PT. The INR and Prothrombin time helps in monitoring the effect of anticoagulants like warfarin. The INR also helps in adjusting the dosage of warfarin. Warfarin helps in inhibiting formation of excess blood clots and maintains normal hemostasis. Warfarin has a role in deep vein thrombosis (DVT), pulmonary embolism (PE), atrial fibrillation etc. The Prothrombin time evaluates the coagulation factors of extrinsic pathway like factors VII, X, V, II and I (fibrinogen). The prothrombin time along with thrombin time helps in evaluating the coagulation factors of common pathway like factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HK). The prothrombin time alone is not useful for the diagnosis of a condition causing bleeding disorders and for the investigations may be needed. The other test include aPTT, thrombin time, platelet count, fibrinogen test, coagulation factor tests. Causes of prolonged PT: 1. Administration of oral anticoagulant drugs (Vitamin K antagonists) 2. The presence of a direct acting inhibitor of factor Xa 3. Liver disease, particularly obstructive jaundice 4. Vitamin K deficiency 5. Disseminated intravascular coagulation 6. Rarely, a previously undiagnosed factor VII, X, V or prothrombin deficiency or defect. Interference in PT and INR: Alcohol, antibiotics, aspirin, cimetidine, thrombin Inhibitors (Increased PT). Barbiturates, oral contraceptives, hormone-replacement therapy (HRT), and vitamin K (Decreased PT). Note: With prothrombin, FX or factor V deficiency the aPTT will also be prolonged.

1. Other than warfarin, what causes prolonged prthrombin time?

Vitamin K deficiency, Liver disease, Hematocrit >55%, Disseminated intravascular coagulopathy, Dysfibrinogenemia, deficiency of extrinsic clotting factor deficiencies (factors II, V, VII, X, fibrinogen), thrombin and factor X inhibitors, gross lipemia of sample, elevated bilirubin, lupus anticoagulants etc, will prolong the prothrombin time.

2. Is the Prothrombin time-INR useful for patients with liver disease?

In persons with a stable chronic liver disease, the Prothrombin time-INR is generally increased (as the clotting factors production is decreased). But if the disease is unstable, the Prothrombin time-INR will not be reliable.