Prothrombin index (PTI) – what is it and how to calculate (formula)

1 19 - 21One of the indicators of a coagulogram is PTI or prothrombin complex, the essence of which is an analysis of the time during which plasma coagulates in human blood.

Subsequently, the obtained indicators are substituted into the formula, and the percentage is expressed.

Normal PTI values ​​show from 78 to 142% according to the Quick’s method, or from 95 to 105% when investigated by other methods.

Determination of the PTI level is a multiplication of the prothrombin time (PT) of the patient individually, by 100% PT of the normal plasma coagulation index. Prothrombin time is the period from the moment when thromboplastin and calcium cells are added to the blood until the moment when a thrombus forms.

PTI shows the activity of blood clotting. A drop in indicators indicates poor clotting, this leads to hemorrhages. An increase in his marks indicates the tendency of the circulatory system to form blood clots, which is fraught with serious illness, or even death.

What is prothrombin itself?

protrombin - 23Prothrombin is a special protein found in the blood and formed in the liver under the influence of vitamin K.

In the case of an insufficient amount of vitamin K, the prothrombin values ​​fall.

Prothrombin is the parent of thrombin, which affects blood clots. This protein directly affects the increase or decrease in blood clotting.

In order to investigate PTI, it is necessary to observe the plasma coagulation rate, for each person in a personal manner, since the indicator depends on the person. The ratio of time between these two values ​​will be the prothrombin index.

If PTI is investigated by the Quick method, then the functioning of prothrombin is detected according to the schedule. This graph gives more accuracy, due to the fact that it is built on the basis of the marks of the results of studies of plasma clotting in dilutions of different concentrations.

mno 3 - 25

Quick analysis results are displayed as a graph

PTI always consists in the analysis of a coagulogram – which is a comprehensive study of blood clotting.

What is the purpose of donating blood for the study of this protein?

Drawing conclusions from the results of such an analysis, a qualified physician can determine:

  • sdayut krov na issledovanie belka - 27Possible heart attack, or pre-stroke condition,
  • The appearance of blood clots, with varicose veins,
  • Does a specific organism need vitamin K,
  • Are there any abnormalities in the liver,
  • What is the state of the blood levels responsible for clotting,

This analysis is especially necessary in case of imminent surgical intervention. Since doctors need to take into account such features, and know the recovery time from injuries.

The pti readings indicate a disorder in blood clotting, which leads to bleeding, or the formation of blood clots. The last two factors can lead to serious complications.

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When is an IPT blood test prescribed?

There are a lot of factors, in the presence of which the doctor can send you for an IPT examination.

Among which:

  • Autoimmune diseases
  • hronicheskie otkloneniya pecheni - 29Chronic liver abnormalities
  • Detection of thromboembolism,
  • With hepatitis,
  • With the death of liver cells (cirrhosis),
  • Oncological diseases,
  • In the event of an upcoming operation,
  • In case of varicose veins,
  • When coagulation abnormalities occur,
  • Checking the effectiveness of therapy,
  • In post-infarction or after a stroke,
  • and other pathologies.

It is imperative that PTI should be monitored regularly for those with heart valve implants, because in these cases its level is increased, which increases the risk of blood clots. And also with cardiovascular pathologies. A coagulogram (including PTI) will help control all these processes.

Normal indicators of PTI

The values ​​of this protein are noted as a percentage. The rates vary, depending on the method of determination. According to Quick, normal levels are from 78 to 142 percent, while according to other studies, from 95 to 105 percent.

The ambiguity of the indicators is associated with the different sensitivity of the reagents; in laboratories of different types, different ones are used. PTI is considered an outdated indicator, and almost not used in modern medicine. It was replaced by the INR (International Normalized Ratio).

Back in 1983, the Ministry of Health introduced this value in order to get the same PT results from different laboratories with different reagents. The INR is not affected by the conditions created by the laboratory, the INR rate shows from 0,82-1,18 for the adult category of people, and from 2 to 3 for anticoagulant therapy.

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Norm for women

As such, there are no differences in the results of levels between women and men. The rates are standard for both sexes.

PTI rate during pregnancy

norma pti pri beremennosti - 31With increased attention, time should be given to the analysis of the coagulogram, and in particular PTI during gestation. All expectant mothers must undergo this procedure. The risk of bleeding or progression of thrombosis during childbirth is determined based on this analysis. With indications, the PTI level is below 80%, is low – as a result of which coagulants are prescribed, so as not to lose a lot of blood during childbirth. If the percentage of concentration is 100, then the therapy is directed in the opposite direction.

Do not skimp on analyzes – this will help save the life of both you and your unborn child. Deciphering the analysis by a qualified doctor is a matter of five minutes. And this will significantly speed up the treatment process.

What affects the low rates of the prothrombin index?

Abnormalities are not good signs and may indicate the presence of various pathologies.

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Its level is reduced possibly for the following reasons:

  • Low presence of vitamin K in the body, which affects blood clotting,
  • In the case of pancreatic cancer,
  • Pancreatic pathology,
  • Chronic blood clotting pathology,
  • Treatment with indirect anticoagulants,
  • When a protein metabolism disorder occurs,
  • Blood oversaturation with heparin,
  • In case of acute leukemia,
  • and other pathologies.

What does PTI grow from?

Several factors contribute to hypercoagulability – a PTI indicator that is significantly higher than the norm.

These include:

  • Congenital coagulation abnormalities,
  • Excess erythrocytes
  • Last months of pregnancy
  • With thrombosis,
  • Cancer tumors
  • With prolonged use of hormonal contraceptives, barbiturates, corticosteroids.

Formula for calculating PTI

The prothrombin index has its own calculation formula:

formula - 33 formula - 33

Normal Indicator Levels and INR Formula

The INR (International Normalized Ratio) gives us the rate of thrombus formation. Norm marks vary, being in direct dependence on characteristics (Table 1):


SituationIndicators of the norm
For the normal course of surgical procedures+0,85
In the presence of chronic atrial fibrillation, thromboembolism of the pulmonary artery and taking “Warfarin”+2,0
After aortic valve and mitral valve implantation, respectively2,5-3,0, 2,5-3,5
With pathologies of the heart valves, and in the case of prevention of thromboembolism+2,0
After surgery, with thrombosis of blood vessels and veins+2,0
With vascular pathologies, or infarction conditions+3,0

For an ordinary person who does not use drugs, the normal mark cannot exceed 1,25.

INR calculation formula

To calculate the INR, there is also a formula:

formula 2 - 37 formula 2 - 37

How to pass the correct coagulogram?

Taking a coagulogram, like any other analysis, to obtain an absolutely accurate result, there are recommendations:

  • Come to the test exclusively on an empty stomach, stop taking food at least 8 hours before the test,
  • If you want to drink, you are allowed to use only clean drinking water without gas. Before delivery, you need to drink 200-250 ml of water (1 glass),
  • No later than a day, do not smoke cigarettes, or quit this habit no later than 2 hours,
  • Don’t worry before donating blood. Coagulability can increase from stressful conditions, and experiences,
  • When using any medication, you need to notify your doctor.


Therapy of certain pathologies and diseases will require a blood clotting result of PTI. They can determine possible hemorrhage, or the formation of blood clots, and prevent many unpleasant diseases. That is why the analysis of the coagulogram, which includes PTI, is used both in therapy and in surgery.

Physicians around the world changed the PTI level to INR, its value is stable, and does not depend on any factors like PTI. Monitoring the indicators of this index will help you to protect yourself in advance from possible blood clots in blood vessels, or hemorrhages.

If symptoms are detected, or if indicators are directly detected that deviate from the norm, in one direction or another, consult a doctor. In this case, treatment cannot be postponed, since PTI is not a separate disease, and its increased blood count only indicates various pathologies and diseases.

Tatyana Jakowenko

Editor-in-chief of the Detonic online magazine, cardiologist Yakovenko-Plahotnaya Tatyana. Author of more than 950 scientific articles, including in foreign medical journals. He has been working as a cardiologist in a clinical hospital for over 12 years. He owns modern methods of diagnosis and treatment of cardiovascular diseases and implements them in his professional activities. For example, it uses methods of resuscitation of the heart, decoding of ECG, functional tests, cyclic ergometry and knows echocardiography very well.

For 10 years, she has been an active participant in numerous medical symposia and workshops for doctors - families, therapists and cardiologists. He has many publications on a healthy lifestyle, diagnosis and treatment of heart and vascular diseases.

He regularly monitors new publications of European and American cardiology journals, writes scientific articles, prepares reports at scientific conferences and participates in European cardiology congresses.