PT INR Normal Values


If you are on anticoagulant medications or showing signs of bleeding problems, it is important that you know the PT INR normal values so you can compare, monitor and determine whether your prescription is working or if indeed you have bleeding problems.

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What is PT INR?

Prothrombin plays a vital role in blood coagulation and is also an important indicator of bleeding issues. Prothrombin time or PT is the test used to check if there are problems in bleeding, especially if the patient is taking the anticoagulant, Warfarin. In order for the prothrombin time to have a standardized calculation, the International Normalized Ratio or INR was made. The INR is the ratio of the prothrombin time of the patient and the prothrombin time normal mean. The PT INR values are the essential parameters that help in monitoringthe effectivenessof anticoagulant medications and confirm whether an individual has blood coagulation disorders or not.

Prothrombin time

Before the health care provider gets the blood sample for the PT test, he or she would confirm if you have taken any medication that can influence the result of the test. If you are on anticoagulant treatment, you should have your blood sample extracted before taking the medication for that day. The laboratory technician would then get a blood specimen either from a vein in your arm by the use of a needle or by a fingerstick. The laboratory would then measure how long it takes for the plasma to clot.

International normalized ratio

The PT varies from one laboratory to another, depending on the instruments and the thromboplastin reagents used. In order to offset the resulting variations, the World Health Organization and the International Committee on Thrombosis and Haemostasis came up with a system of presenting PT results that can be used even when comparing results of tests performed by different laboratories.  This system allows for the standardization of results by calculating the International Normalized Ratio.  This way, no matter how many different laboratories checked your PT INR, you should be able to get the same result.  You would then be able to monitor and compare your results to the PT INR normal values.

The following figures are considered to be PT INRnormal values depending on your condition. Your medications will be adjusted so that the appropriate PT INR values can be obtained.

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  • 2 to 3 – for VTE prevention (venous thromboembolism)
  • 2 to 3 – for VTE, valvular heart disease and pulmonary embolus treatment
  • 3 to 4.5 – for arterial thromboembolism, recurrent systemic embolism and mechanical heart valves treatment

Your PT INR values should be screened as often as needed in order for the health care provider to keep track of the effectiveness of the anticoagulant therapy or any improvements or changes in your condition especially if you have observedbleeding problems. When the results are within the PT INR normal values, then you are considered safe from too much bleeding tendencies, however, constant monitoring is still needed. If the PT INR values suddenly go up or are prolonged, there is something amiss in your body.You may be suffering from diseases or disorders such as Vitamin K deficiency, Disseminated Intravascular Coagulation, Bile Duct Obstruction, orFactor I, II, V, VII and X deficiency.

Factors that can affect PT INR normal values

There are certain things that can affect the PT INR results. Medications such as antibiotics, oral contraceptives, and barbiturates can affect the values of the prothrombin time and international normalized ratio. Consuming foods such as soybeans, green tea, beef, pork liver and foods rich in vitamin K can make the results go out of range of the PT INR normal values as well. Drinking alcohol also changes the result of the test. Therefore, thorough medical history should be taken so that the interpretation of the PT INR results is accurate.

When is PT INR Required?

The PT INR test is generally required if you are on anticoagulant therapy as this is the tool used in monitoring your condition and how effective the medication is performing.  The test checks whether the treatment you are on sufficiently maintains the PT INR normal values appropriate for you.  There is no set frequency as to when and how often the screening should be done; it is up to the physician’s discretion as long as it is assured that your PT is high enough but without resulting to bruising or bleeding problems.

However, gender and age may influence how frequent the test is required.  Conditions that have become progressive or chronic, or has improved or deteriorated, may also require more frequent screenings.

Individuals who show signs of bleeding problems are also required to have the PT INR test. It is also common for patients who need surgery to be ordered the test to ascertain that there are no clotting problems during and after the invasive procedure.

If you fall into any of the above groups of people, you should know the PT INR normal values right for you and be able to compare and monitor your results so that the necessary steps can be done should something goes amiss.

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