Prothrombin time PT/PT-INR


Prothrombin time (PT) is a blood test that determines how long blood takes to clot. To screen for bleeding issues, a prothrombin time test might be utilised. PT is also used to determine whether blood clot prevention medication is effective. A PT test is also known as an INR test. The term INR (international normalised ratio) refers to a means of normalising the findings of prothrombin time tests, regardless of the testing method used. It enables your doctor to interpret results in the same way, even if they originate from multiple labs and test procedures. Clotting factors are required for blood to clot (coagulation). Prothrombin, also known as factor II, is a clotting agent produced by the liver. Vitamin K is required for the production of prothrombin and other clotting components. The prothrombin time test is essential because it determines the presence of five separate blood clotting factors (factors I, II, V, VII, and X). The following factors increase the prothrombin time. For patients on vitamin K antagonists, the preferred test is the international normalised ratio (INR) (VKA). It can also be used to measure a patient’s risk of bleeding or coagulation status. Because INR varies between patients, patients taking oral anticoagulants must monitor their INR to adjust their VKA doses. 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

The time in seconds required in plasma to form a clot in the presence of appropriate calcium and tissue thromboplastin concentrations by activating coagulation via the extrinsic pathway is measured as PT. The reference values for INR take into consideration device-related changes, reagent type, and sensitivity differences in the TF activator when measuring PT. The value of INR is dimensionless and varies from 2.0 to 3.0(J.A. Doerr, R.D. Wyatt, P.B. Hamilton,Investigation and Standardization of Prothrombin Times)

What is Prothrombin?

Prothrombin is a protein that is produced by the liver. It’s one of a group of compounds known as clotting (coagulation) factors. When you acquire a cut or another type of injury that causes bleeding, your clotting factors join forces to form a blood clot. Too little clotting factor can cause you to bleed excessively after an accident(.Shigetoshi Fujiyama MD, Takafumi Morishita MD, Osamu Hashiguchi).


Prothrombin is a glycoprotein (carbohydrate-protein complex) found in blood plasma that is required for blood clotting. A clotting factor known as factor X or prothrombinase converts prothrombin to thrombin; thrombin then proceeds to turn fibrinogen, which is also present in plasma, into fibrin, which, when combined with blood platelets, produces a clot (a process called coagulation). Under normal conditions, prothrombin is converted to thrombin only when tissues or the circulatory system, or both, are injured; thus, fibrin and blood clots are not generated except in reaction to bleeding. Hypoprothrombinemia, or a prothrombin deficit, is characterised by a proclivity for prolonged bleeding. It is commonly related to a deficiency in vitamin K, which is required for the formation of prothrombin in liver cells. In adults, the disease is most common in cases of obstructive jaundice, in which the passage of bile to the gut is disrupted—bile is required for vitamin K absorption in the intestine. It can also be caused by a general deterioration in the liver and intestinal cell activity, as well as an overdose of warfarin and other anticoagulants.

Prothrombin time

Prothrombin is a protein that is produced by the liver. Prothrombin aids in the clotting of blood. The “prothrombin time” (PT) is a unit of measurement used to determine how long it takes blood to clot. It is measured in seconds (such as 13.2 seconds). A normal PT suggests that there is an adequate supply of blood-clotting protein.

Test results explanation:

When the PT is high, the blood takes longer to coagulate (17 seconds, for example). This usually occurs when the liver does not produce enough blood-clotting proteins, causing the clotting process to take longer. A high PT usually indicates severe liver disease or cirrhosis. A high PT may suggest an increased risk of internal bleeding from the upper GI tract.

Why it is done?

Prothrombin time (PT) is measured to:

  • Find a cause for abnormal bleeding or bruising.
  • Check the effects of warfarin (Coumadin). You will have the test regularly to make sure you are taking the right dose.
  • Check for low levels of blood clotting factors. The lack of some clotting factors can cause bleeding disorders such as haemophilia, which is passed in families (inherited).
  • Check if it is safe to do a procedure or surgery that might cause bleeding.
  • Check how well the liver is working. Prothrombin levels are checked along with other liver tests, such as aspartate aminotransferase and alanine aminotransferase.
  • Check to see if the body is using up its clotting factors so quickly that the blood can’t clot and bleeding does not stop. This may mean the person has disseminated intravascular coagulation (DIC).

A needle is used by a health expert to draw a blood sample, usually from the arm. In rare situations, the health expert will draw a blood sample from your fingertip rather than your vein. The health expert will clean your hand, use a lancet to puncture the skin, and place a tiny tube on the puncture site to collect your blood for a finger stick blood test.


There is little danger in getting your blood drawn. The size of veins and arteries varies from person to person and from one side of the body to the other. It may be more difficult to obtain a blood sample from some persons than from others. Other minor dangers linked with having blood collected include:

Fainting or feeling dizzy

  • Hematoma (blood accumulating under the skin)
  • Multiple punctures to locate veins
  • Infection (a slight risk any time the skin is broken)

This test is often done on people who may have bleeding problems. Their risk of bleeding is slightly higher than for people without bleeding problems.

Normal Outcomes

The time it takes to complete a PT test is measured in seconds. The majority of the time, the results are presented in Indian rupees (INR) (international normalised ratio). If you are not using blood thinners like warfarin, the usual range for your PT values is:

Normal Results

PT is measured in seconds. Most of the time, results are given as what is called INR (international normalized ratio)(3).

If you are not taking blood-thinning medicines, such as warfarin, the normal range for your PT results is:

  • 11 to 13.5 seconds
  • INR of 0.8 to 1.1\

f you’re taking warfarin to avoid blood clots, your doctor will probably keep your INR between 2.0 and 3.0. Inquire with your provider about the best outcome for you. Normal value ranges may differ slightly between laboratories. Some labs employ various metrics or test various samples. Discuss the significance of your test results with your clinician.     (Ansell, J., Hirsh, J., Poller, L., Bussey, H., Jacobson, A., & Hylek, E. (2004.

What Do Abnormal Results Indicate?

If you are not using a blood-thinning medication, such as warfarin, an INR of more than 1.1 indicates that your blood is clotting more slowly than usual. This could be b::Bleeding disorders are a range of illnesses in which the body’s blood coagulation process fails.

 A disorder in which the proteins that govern blood clotting become overactive (disseminated idiopathic clotting)

What Abnormal Results Mean

If you are not taking blood-thinning medicines, such as warfarin, an INR result above 1.1 means your blood is clotting more slowly than normal. This may be due to(Poort, S. R., Rosendaal, F. R., Reitsma, P. H., & Bertina, R. M. (1996):

  • Bleeding disorders, a group of conditions in which there is a problem with the body’s blood clotting process.
  • Disorder in which the proteins that control blood clotting become overactive (disseminated intravascular coagulation).
  • Liver disease.
  • Low level of vitamin K.

If you’re taking warfarin to prevent clots, your doctor will probably keep your INR between 2.0 and 3.0:The desired amount may differ depending on why you are taking the blood thinner. Even if your INR remains between 2.0 and 3.0, you are more likely to experience bleeding issues.(Franchini, M., & Lippi, G. (2010).

What Do the Findings Imply?

The test will tell how long it took your blood to clot. What is typical varies depending on the lab, so see your doctor help understand what your statistics imply. A typical PT time ranges from 10 to 14 seconds. Higher than that indicates that your blood is taking longer than usual to clot, which could be a sign of a variety of diseases, including.( Owren, P. A., & Aas, K. (1951):

  • Bleeding or clotting disorder
  • Lack of vitamin K
  • Lack of clotting factors
  • Liver disease

Vitamin K and Prothrombin

Vitamin K is classified into two types: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). The former is primarily found in plant-based meals. The latter, on the other hand, is found in animal-sourced foods. Vitamin K1 is abundant in kale, mustard greens, spinach, and broccoli. Beef liver, pig chops, and chicken, on the other hand, are high in vitamin K2. Vitamin K2 is found in the highest concentrations in fatty foods and the liver. You can also acquire enough of this nutrient by eating bacon, duck breast, and chicken liver.