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Prothrombin Time (PT, INR)

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The measurement of prothrombin time and INR is used as an initial screening test to detect deficiencies of one or more coagulation factors (Factors I, II, V, VII, X) as well as to monitor patients on anticoagulation.

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The hemostatic process involves many steps and the proper functioning of a wide variety of coagulation factors and other substances. Prothrombin Time (PT) is used to evaluate how well the coagulation process works. This test is useful in detecting blood clotting disorders caused by either deficiency or defective function of the coagulation factors that make up the extrinsic system. These factors include fibrinogen (factor I), prothrombin (factor II) and factors V, VII, and X. If the patient's blood is deficient in one of these factors, the patient's PT (measured in seconds) will be higher than the control PT (measured in seconds).

PT is also used to monitor the efficacy of anticoagulant therapy with warfarin (Coumadin). This drug interferes with the production of vitamin K-dependent coagulants, such as prothrombin. PT involves measuring the time it takes for a clot to form in a plasma sample after the addition of calcium and thromboplastin.

In order to compare the results of PT between different laboratories, the World Health Organization recommends the use of International Normalized Ratio (INR). Diagnostiki Athinon’s report includes both PT and INR results.

Maintaining an INR between 2.0-3.0 (mild anticoagulant therapy) is recommended for the prophylaxis and treatment of venous thrombosis and thromboembolic complications associated with vaginal fibrillation, pulmonary embolism, prophylaxis of systemic and post-infarct embolism heart valves. A higher INR 2.5-3.5 (intensive anticoagulation) is recommended for mechanical heart valve replacement and for antiphospholipidemic syndrome.

The frequency of testing to achieve and maintain the recommended INR level is based on the patient's clinical condition. In the case of warfarin overdose with subsequent bleeding, the antidote is vitamin K, which reverses the action of warfarin in 12 to 24 hours.

Possible Interpretations of Pathological Values
  • Increase: Aninogenemia, alcoholism, biliary obstruction, cancer, celiac disease, anticoagulation, cirrhosis, colitis, collagen disease, congestive heart failure, diarrhea (chronic), diffuse intravascular coagulation (DIC), DIC, V , VII, X), fever, syringe, neonatal hemorrhagic disease, hepatic disease (abscess, biopsy, deficiency, jaundice, infectious hepatitis), hyperinfluence, hyperthyroidism, hypervitaminosis A, hypovitogenemia (hypokinogenemia) (<100 mg / l) myelofibrosis, increased fiber doloric activity, jaundice (hemolytic, hepatocellular, obstructive), leukemia (acute), malabsorption, malnutrition, obstetric complications, pancreatic cancer, pancreatitis (chronic), genuine polycythemia, high polycythemia, premature cerebral palsy, snake bite, stearorrhea, toxic shock syndrome, vitamin K deficiency, vomiting.Medications: Alcohol, allopurinol, aminosalicylic acid, amiodarone HCl, anabolic steroids, antibiotics, bromelain, chinodioli, chloral hydrate, chlorpropamide, chymotrypsin, cimetidine, clofibrate, dextran, dextrothyroxine, diazoxide, diflunisal, disulfiram, diuretics, ethacrynic acid, fenoprofen, fluoroquinolone , fluoxetine, glucagon, hepatotoxic drugs, ibuprofen, indomethacin, influenza virus vaccine, mephenamic acid, methyldopa, methylphenidate, metronidazole, miconazole, monoamine oxidase inhibitors naproxen, drug (extended use), pentoxifylline, phenylbutazone, phenytoin, propafenone, pyrazolones, quinidine, quinine, ranitidine, salicylates, sulfinpyrazone, sulfonamides (long acting), sulindac, tamoxifen, thyroid drugs, tolbutamide, trimethoprim-sulfamethoxazole, warfarin
  • Decrease: Arterial obstruction, deep vein thrombosis, edema, hereditary resistance to coumarin, hyperlipidemia, hyperthyroidism, hypothyroidism, multiple myeloma, myocardial infarction, peripheral vascular disease. Medications: Steroids, alcohol, aminoglutethimide, antacids, antihistamines, barbiturates, carbamazepine, chloral hydrate, chlordiazepoxide, cholestyramine, diuretics, glutethimide, griseofulvin, haloperidol, meprobamate, nafcillin, oral contraceptives, paraldehyde, primidone, ranitidine, rifampicin, sucralfate, trazodone, vitamin C, warfarin (low dose)
Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.

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