PTT (activated partial thromboplastin time) is the rate of formation of a blood clot in a plasma sample after adding calcium chloride and other reagents to it. This indicator is determined as part of the study of the hemostasis system and reflects the characteristics of the internal pathway and the general cascade of the coagulation process. PTT test is necessary in the diagnosis of hemophilia, deep hypofibrinogenemia, dysfibrinogenemia, disorders of fibrin monomer polymerization, to assess the effectiveness of treatment with direct anticoagulants, as well as in preparation for surgery. Blood sampling for analysis is performed from a vein. The study is carried out by the method of detecting lateral light scattering, determining the percentage at the endpoint. Normally, the values obtained are in the range from 21 to 36.5 seconds. The timing of the analysis is no more than 1 working day.
PTT (partial thromboplastin time) is one of the basic indicators of the hemostasis system. Its definition has important diagnostic and prognostic value in many areas of clinical practice. If a vessel is damaged in the body, the process of blood clotting and stopping bleeding starts. It consists of three stages: the damaged vessel spasms, a clot forms from platelets, a coagulation cascade is triggered in the blood plasma – a chain of reactions during which coagulation factors are activated one after another, and a stable thrombus is formed.
PTT is the main indicator of the coagulation cascade, internal and general (final) coagulation pathways. During the laboratory test, a reagent is injected into the blood plasma, triggering the sequential formation of coagulation factors, after the incubation period, calcium chloride and partial thromboplastin are added to the mixture – the natural process of coagulation along the internal pathway is simulated. Based on the rate of reactions, an increased risk of bleeding (high rates) or thrombosis (low rates) is determined.
The biomaterial for PTT test is venous blood. The clotting time of platelet-free plasma with a reagent containing phospholipids is most often determined using an automatic analyzer. PTT test is a fundamental study of the hemostasis system. The results are in demand in many areas of clinical practice. In hematology, they are used to diagnose and monitor diseases based on blood clotting disorders: thrombosis, hemophilia, etc. Evaluation of the hemostasis system is important in situations involving large blood loss, therefore, these tests are used in surgery and traumatology in preparation for operations, in obstetrics and gynecology in preparation for childbirth and to detect antiphospholipid syndrome. The data of this analysis are used in many areas where the assessment of the hemostasis system is important: in cardiology, phlebology, oncology, endocrinology.
Indications and contraindications
A blood test for PTT is indicated for symptoms that indicate a violation of blood clotting. With a decrease in the speed of this process, subcutaneous hematomas are often formed, prolonged bleeding is observed: nasal, menstrual, post-traumatic. With an increase in the index, vascular asterisks and nodes on the legs, bruises (due to the fragility of the vessels), weakness and drowsiness occur. The study is prescribed for the diagnosis of hemophilia, deep hypofibrinogenemia, dysfibrinogenemia, DIC syndrome, deep vein thrombosis, pulmonary embolism, myocardial infarction, kidney or intestine. The analysis is also carried out during the treatment of these diseases, especially if anticoagulant therapy with heparin and its low-molecular forms is used.
The PTT test is performed as part of a comprehensive study of the hemostasis system (coagulogram) as part of screening during pregnancy, in the presence of risk factors for thrombosis or hemophilia (heredity). The analysis is indicated when preparing patients for operations, invasive diagnostic procedures, childbirth – for any processes accompanied by the risk of blood loss. In women of childbearing age, it is carried out to establish the causes of infertility, miscarriage if antiphospholipid syndrome is suspected.
Although the PTT indicators within the reference values indicate normal coagulatory function of the blood along the internal and general pathway, they do not exclude a moderate deficiency of clotting factors or a moderate presence of process inhibitors (for example, lupus anticoagulant). With severe blood clotting disorders, a blood test is contraindicated, since there is a high risk of bleeding during blood collection. Also, the procedure is not performed in patients with psychomotor agitation, severe arterial hypotension or anemia.
The advantage of this test is its high accuracy: in laboratory conditions, it is possible to recreate the natural process of blood clotting and identify violations of its speed. However, an isolated interpretation of the results is unacceptable, since they do not allow to fully assess the features of coagulation. In clinical practice, PTT analysis is performed in conjunction with the study of INR, D-dimer, prothrombin time, prothrombin index, fibrinogen.
Preparation for analysis and material collection
When determining the PTT, venous blood is examined. Special preparation for the sampling procedure is not required. It is carried out, as a rule, in the morning, on an empty stomach. The last meal should be done in 12 hours, at the very least, the break can be from 6 to 4 hours. Clean water is allowed to drink. Within 30 minutes before taking blood, it is necessary to limit physical activity and the influence of stress factors, exclude smoking. Some medications may affect the result, so you need to warn your doctor or laboratory assistant about taking them.
Blood is taken by puncture from the ulnar vein and placed in a test tube with a solution of sodium citrate, after which the biomaterial and anticoagulant are gently mixed, excluding shaking. An indispensable condition for obtaining the correct result of the study is the exact ratio of the amount of blood taken and the anticoagulant – it should be 9:1. No more than 6 hours may pass from the moment of blood collection to the examination. In the laboratory, platelets are removed from the blood by centrifugation. Then phospholipids and a kaolin suspension (contact activator) are added to the test tube, and a chain of reactions involving coagulation factors is triggered in response. After a certain time, calcium chloride is injected and the time for which the clot was formed is determined. In the standard operating mode of the laboratory, the results of the analysis can be found out the next day, in emergency situations – 2 hours after blood collection.
Normal values
A normal PTT for adults and children is considered to be an indicator in the range from 21 to 36.5 seconds. Higher values are observed during the newborn period – from 22 to 40 seconds (in premature babies – from 27 to 42 seconds). The reference values may vary depending on the reagents used and the features of the automatic analyzer, therefore, for greater reliability, they should be determined by the results form of the laboratory that performed the analysis. If the data obtained fall within the normal range, this indicates the adequate functioning of the coagulation mechanism along the internal and general pathway, but a moderate lack of any clotting factor or a moderate presence of lupus anticoagulant is not excluded.
Minor deviations from the norm are detected if there are impurities of heparin or other direct anticoagulants in the blood sample, for example, in cases when solutions with these substances are used for the treatment of test tubes and cannulas. The result can be affected by the consumption of fatty foods and smoking on the eve of taking the material. A slight decrease in PTT is observed in the last trimester of pregnancy as part of the natural adaptation of the woman’s body to delivery, as well as during menstruation.
Raising the level
The reasons for the increase in PTT indicators are diseases with congenital or acquired deficiency of clotting factors. These include: Willebrand’s disease, Hageman’s disease, hemophilia (A, B and C), leukemia, phases 2 and 3 of DIC syndrome, antiphospholipid syndrome. The increase in coagulation time may be due to vitamin K deficiency caused by extreme diet, malabsorption syndrome, kwashiorkor, alimentary dystrophy, prolonged use of antibiotics, dysbiosis. Liver diseases also lead to the inability of the body to synthesize blood clotting factors, which is manifested by an increase in the test parameters.
The reason for the increase in PTT indicators may be the presence of nonspecific coagulation inhibitors in the blood, such as lupus anticoagulant, anticardiolipin antibodies, antibodies to phospholipids. In patients with hemophilia, antibodies against factor VIII are produced against the background of long-term therapy, the activity of which is expressed by an increase in the final values of the test.
Lowering the level
The reason for the decrease in PTT indicators is the body’s tendency to thrombosis, which indicates the presence of thrombosis or thromboembolism – gradual or rapid blockage of medium and large vessels by a blood clot. Also, the shortening of the coagulation time occurs in phase 1 of the DIC syndrome, especially in children, and with an increase in factor VIII as a result of an inflammatory reaction in the body, chronic disease, pathology of the kidneys, liver, oncological neoplasm. The reason for the decrease in PTT indicators may be a tissue thromboplastin that got into the blood sample with an incorrectly performed venipuncture.
Treatment of abnormalities
PTT test is used in many areas of clinical practice. Its results help to evaluate the functions of the blood coagulation system, diagnose diseases associated with a violation of the coagulation process, and monitor heparin therapy. Timely detection of deviations allows you to shorten the time and increase the effectiveness of treatment. With the results of the study, it is worth contacting the attending physician who issued the referral for analysis, or to the therapist to determine further tactics. You can correct physiological deviations from the norm yourself by reducing the consumption of fatty foods and giving up smoking.
