How is PT INR calculated?
The INR is derived from prothrombin time (PT) which is calculated as a ratio of the patient’s PT to a control PT standardized for the potency of the thromboplastin reagent developed by the World Health Organization (WHO) using the following formula: INR = Patient PT ÷ Control PT.
Is PT ratio same as INR?
A prothrombin time (PT) is a test used to help detect and diagnose a bleeding disorder or excessive clotting disorder; the international normalized ratio (INR) is calculated from a PT result and is used to monitor how well the blood-thinning medication (anticoagulant) warfarin (Coumadin®) is working to prevent blood …
How is ISI calculated?
The slope of the line is calculated and this represents the ISI. So if the ISI of the Reference Thromboplastin is 1.1 and the ISI derived from the slope is 1.14, the ISI of the Test Thromboplastin is 1.1 x 1.14 = 1.25.
What is a normal PT INR range?
In healthy people an INR of 1.1 or below is considered normal. An INR range of 2.0 to 3.0 is generally an effective therapeutic range for people taking warfarin for disorders such as atrial fibrillation or a blood clot in the leg or lung.
Why we add ISI in the INR formula?
The international normalized ratio (INR)/international sensitivity index (ISI) system was introduced to standardize PT variation with the use of different thromboplastin reagents. The ISI of each thromboplastin represents a responsiveness to the reduction of coagulation factors.
What does a PT INR of 1.0 mean?
A result of 1.0, up to 1.5, is therefore normal. A low INR result means your blood is ‘not thin enough’ or coagulates too easily and puts you at risk of developing a blood clot. A high INR result means your blood coagulates too slowly and you risk bleeding.
What is the formula to calculate INR?
The INR uses the ISI to equate all thromboplastins to the reference thromboplastin through the following equation: INR = (patient PT/mean normal PT) ISI. Thus, the INR can be calculated using the working prothrombin time ratio once the ISI of the thromboplastin is known.
What is the normal range of PT and INR?
Normal values. The normal PT ranges from ten to thirteen seconds. As INR is a ratio, the general population will have a value of about 1. After taking into consideration the differences across the general population, the INR ranges between 0.8 and 1.2 among them.
What is the difference between INR and PT?
PT and INR are both measures of how long it takes your blood to clot, expressed in two different ways. PT stands for prothrombin time. It is a measure in seconds of how long it takes your blood to clot. The results of the PT test vary depending on the laboratory, the test chemicals used in different laboratories and the method used to test blood.
What do your PT, PTT, and INR results mean?
PT/PTT are laboratory tests that measure the clotting time (how long it takes blood to clot.) PT/PTT are blood tests and INR is a ratio calculated from the PT. At least a dozen blood proteins, or blood clotting factors, are needed to clot blood and stop bleeding (coagulation).