Prothrombin Time (PT) & International Normalize Ration (INR)

Prothrombin Time (PT) & International Normalize Ratio (INR)

Introduction

An INR is useful in monitoring the impact of anticoagulant (“blood thinning”) medicines, such as Warfarin(Coumadin). Patients with atrial fibrillation often take anticoagulant medications to protect against clots that can cause strokes. While taking Warfarin, patients have regular blood tests to monitor their INR. Just as patients know their blood pressure numbers, they also should know their Warfarin (Coumadin) dosage and their INR.

This standarization system was introduced by World Health Organization (WHO) in 1983 to provide a common basis for the interpretation of the PT result independent of the sensivity of the thromboplastin reagen which tends to vary from one manufacturer to another

Normal Result Of Prothombin Time

Although there is some variation depending on the source of the thromboplastin used in the test. (For this reason, laboratories report a normal control value along with patient results.) A prothrombin time within this range indicates that the patient has normal amounts of clotting factors VII and X.

The Normal Prothrombin Time (PT) is 11-15 seconds

Abnormal Results Of Prothombin Time

A prolonged PT time is considered abnormal. The prothrombin time will be prolonged if the concentration of any of the tested factors is 10% or more below normal plasma values. A prolonged prothrombin time indicates a deficiency in any of factors VII, X, V, prothrombin, or fibrinogen.

It may mean that the patient has a vitamin K deficiency, a liver disease, or disseminated intravascular coagulation (DIC). The prothrombin time of patients receiving warfarin therapy will also be prolonged-usually in the range of one and one half to two times the normal PT time. A PT time that exceeds approximately two and a half times the control value (usually 30 seconds or longer) is grounds for concern, as abnormal bleeding may occur.

Formula

INR = Patient PT / Mean Of Normal Patient Range

Interpretation (INR)

• 1.0 : For Healthy People,
• 2.0 - 3.0 : For patients on anticoagulants, or patients with atrial fibrillation,
• 3.0 - 4.0 : For patients with mechanical heart valves.
• > 4.0 : Indicate that blood is clotting too slowly (High Risk For Uncontrolled Bleeding)

The Ideal INR must be individualized for each patient

While the INR reporting format may improve the management of anti-coagulanted patient, the INR inapproriate in three subsets, such as :

1. The System was designed for patient who are stabilized on oral anticoagulant therapy and is not appropriate for those patient who have recently begun their treatment.
2. Patient with liver disease should not be monitored by the INR since they frequently lack circulating factors
3. Patient who are being routinely screened for clotting factors deficiencies.

Food & Drug Effects

Do not take any prescription or nonprescription medicines without first talking to the doctor who tracks your INR test results. Foods high in vitamin K, a natural blood-clotting factor, can alter an INR. Broccoli, lettuce, spinach and liver are all high in vitamin K. Doctors usually encourage patients to include these nutritious foods in a healthy diet. It is important, however, to consume a consistent amount of these foods and not drastically change eating habits. It is important to have follow up blood tests as scheduled by your doctor and to know your Warfarin (Coumadin) dosage and INR.

Many Food & Drugs Can Change The INR such as :
Aspirin, Ibuprofen, Antibiotics, Vitamin K, Brocolli, Lettuce, Spinach, and Birth Control Pills/Progesterone-Estrogen Combination Pills.

Want More Tips, Tricks, & Informations About Internal Medicine? Click Here To Subscribe To Our Newsletter. Totally FREE.