The measurement of prothrombin time and INR is used as an initial screening test to detect deficiencies in one or more coagulation factors (factors I, II, V, VII, X) and monitor patients on anticoagulant therapy.
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Hemostasis involves many steps and the proper functioning of various clotting factors and other substances. Prothrombin Time (PT) assesses how well the clotting process is working. This test helps detect blood clotting disorders caused by either a deficiency or defective function of the clotting factors that make up the extrinsic system. These factors include fibrinogen (factor I), prothrombin (factor II), and factors V, VII, and X. If a patient's blood is deficient in one of these factors, the patient's PT (measured in seconds) will be higher than the control's PT (measured in seconds).
The PT is also used to monitor the effectiveness of anticoagulant therapy with warfarin (Coumadin). This drug interferes with producing vitamin K-dependent clotting factors, such as prothrombin. PT involves measuring the time it takes for a clot to form in a plasma sample after adding calcium and thromboplastin.
The World Health Organization recommends using the International Normalized Ratio (INR) to compare PT results between different laboratories. Diagnostiki Athinon results report both PT and INR.
Maintaining an INR between 2.0-3.0 (mild anticoagulation) is recommended for the prophylaxis and treatment of venous thrombosis and thromboembolic complications associated with atrial fibrillation, pulmonary embolism, the prophylaxis of systemic embolism after myocardial infarction, and bioprosthetic heart valves. A higher INR of 2.5-3.5 (intensive anticoagulation) is recommended in mechanical heart valve replacement and antiphospholipid 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 a warfarin overdose with subsequent bleeding, the antidote is vitamin K, which reverses the effect of warfarin within 12 to 24 hours.
Possible Interpretations of Pathological Values
- Increase: Afibrinogenemia, alcoholism, biliary obstruction, cancer, celiac disease, anticoagulants, cirrhosis, colitis, collagen disease, congestive heart failure, diarrhea (chronic), disseminated intravascular coagulation (DIC), dysfibrinogenemia, coagulation factor deficiency (I, II, V, VII, X), fever, fistulas, hemorrhagic disease of the newborn, liver disease (abscess, biopsy, deficiency, jaundice, infectious hepatitis), hypernephroma, hyperthyroidism, hypervitaminosis A, hypofibrinogenemia (<100 mg/dL), idiopathic familial hypoprothrombinemia, idiopathic myelofibrosis, increased fibrinolytic activity, jaundice (hemolytic, hepatocellular, obstructive), leukemia (acute), malabsorption, malnutrition, obstetric complications, pancreatic cancer, pancreatitis (chronic), polycythemia vera, premature infants, very high ambient temperature, prothrombin deficiency, Reye's syndrome, snakebite, steatorrhea, toxic shock syndrome, vitamin K deficiency, vomiting. Medications: Alcohol, allopurinol, aminosalicylic acid, amiodarone hydrochloride, anabolic steroids, antibiotics, bromelain, chenodiol, chloral hydrate, chlorpropamide, chymotrypsin, cimetidine, clofibrate, dextran, dextrothyroxine, diazoxide, diflunisal, disulfiram, diuretics, ethacrynic acid, fenoprofen, fluoroquinolone, fluoxetine, glucagon, hepatotoxic drugs, ibuprofen, indomethacin, influenza vaccine, mefenamic acid, methyldopa, methylphenidate, metronidazole, miconazole, monoamine oxidase inhibitors, nalidixic acid, naproxen, narcotics (long-term use), pentoxifylline, phenylbutazone, phenytoin, propafenone, pyrazolones, quinidine, quinine, ranitidine, salicylates, sulfinpyrazone, sulfonamides (long-acting), sulindac, tamoxifen, thyroid medications, tolbutamide, trimethoprim-sulfamethoxazole, warfarin
- Decrease: Arterial occlusion, deep vein thrombosis, edema, hereditary coumarin resistance, hyperlipidemia, hyperthyroidism, hypothyroidism, multiple myeloma, myocardial infarction, peripheral vascular disease, pulmonary embolism, spinal cord injury, thromboembolism (acute), graft rejection. 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 dosage)
Important Note
Laboratory test results are the most critical parameter for diagnosing and monitoring all pathological conditions. Between 70 to 80% of diagnostic decisions are based on laboratory tests. Correctly interpreting 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 analyzed based on each case and family history, clinical findings, and the results of other laboratory tests and information. Your 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 contact your doctor to ensure you receive the best possible medical care.
