The prothrombin time or PT is a blood test that evaluates the blood’s ability to clot, that is, the time needed to stop bleeding, for example. Thus, the prothrombin time test is used whenever bleeding or frequent bruising appears to try to find the cause of the problem, as well as when there is suspicion of liver problems, and the dosage of TGO, TGP and GGT is also requested, for example.
Prothrombin, also known as clotting factor II, is a protein produced by the liver and when activated promotes the conversion of fibrinogen into fibrin, which, together with platelets, forms a layer that prevents bleeding. Thus, prothrombin is an essential factor for blood clotting to take place. Understand how clotting happens.
Reference values
The prothrombin time reference value for a healthy person should vary between 10 and 14 seconds, which may vary from laboratory to laboratory according to the reagent used and laboratory equipment used for analysis.
In addition to the TP, the INR, which aims to standardize the result worldwide, which allows for a more accurate assessment of the development of diseases and the effect of the use of anticoagulant drugs, for example. Thus, the value of the INR for healthy people should vary between 0.8 and 1. However, in the case of using oral anticoagulants, the value should be between 2 and 3, depending on the disease that led to the need for treatment with this type of medication.
How to calculate INR
The calculation of the INR, also called the RNI, is done by the laboratory, taking into account the reagents used. To calculate the INR, the following factors are needed:
- prothrombin time (PT);
- Mean normal prothrombin time (NMRPT);
- International Sensitivity Index (ISI), which is provided by the manufacturer of each lot of thromboplastin reagent.
The calculation of the INR is done following the following formula: INR = (TP/TMPN) ISI.
what does the result mean
The result of the prothrombin time test can be altered due to different causes, so whenever there are changes, the doctor can order new tests to be able to identify the correct cause and start treatment. Some of the most common causes include:
high prothrombin time
This result indicates that if a cut does occur, the bleeding will take longer to stop, with some of the most common causes including:
- Use of anticoagulants;
- Change in intestinal flora;
- Poorly balanced diet;
- Liver diseases;
- Vitamin K deficiency;
- Coagulation problems such as hemophilia;
In addition, some medications such as antibiotics, corticosteroids and diuretics can also change the value of the exam, so it is advisable to inform the doctor about all the medication being used.
low prothrombin time
When the prothrombin value is lower, it means that clotting happens very fast. So, although bleeding is rarer and stops quickly, there is a greater risk of clot formation that can lead to a heart attack or stroke.
Some of the causes that can cause this change include:
- Use of vitamin K supplements;
- Excessive consumption of foods with vitamin K, such as spinach, broccoli or liver;
- Use of estrogen-containing pills, such as birth control pills.
In these cases, it may be necessary to start using anticoagulants or heparin injections until the cause of the change is identified. After that, the doctor will recommend the most appropriate treatment.
