Prothrombin time test

Thromboplastin A substance that triggers the coagulation cascade. Tissue factor is a naturally-occurring thromboplastin and is used in the prothrombin time test. 

Vitamin K status can be assessed by a functional test, called the "prothrombin time test," which involves measuring the lime required to form a blood clot. The test is performed as follows. A blood sample is withdrawn from a subject and immediately mixed with citric acid. Citric acid is a chelator, which means that it can form a tight complex with ions, such as calcium ions. The chelator prevents the interaction of calcium ions with the blood-clotting proteins and thus prevents these proteins from forming a blood clot in the sample. Calcium ions, it should be noted, are required for supporting the activity of several blood clotting proteins. The "citrated blood" is placed in a machine called a fibrometer. The fibrometer is used to detect increases in the viscosity of the blood over a period. 

Traditionally, vitamin K status has been measured by the prothrombin test, mentioned earlier. This method is not sensitive to mild vitamin K deficiency, as values acquired by the prothrombin hme test do not change until the concentration of prothrombin (in the blood sample) declines by 50% or greater. In one recent study, the normal value for the prothrombin time test was 12 seconds (Sokotl ct aL, 1997). 

Ts ao C, Swedlund J, Neofotistos D. Implications of use of low international sensitivity index thromboplastins in prothrombin time testing. Arch Pathol Lab Med 1994 118 1183-7. 

Prothrombin time test (PT) Laboratory test used to monitor the anticoagulant effect of warfarin prolonged when drug effect is adequate... 

During the next week, the patient was started on warfarin and her heparin was discontinued. Two months later, she returned after a severe nosebleed. Laboratory analysis revealed an INR (international normalized ratio, the system now used for reporting results of the prothrombin time test) of 7.0 (INR value in such a warfarin-treated patient should be 2.5-3.5). In order to prevent severe hemorrhage, the warfarin should be discontinued and this patient should be treated immediately with... 

The prothrombin time test (PT, Pro-Time, tissue factor induced coagulation time) is the most eommon method employed in clinical situations. It measures the time taken for a fibrin elot to form in a citrated plasma sample eontaining ealeium ions and tissue thromboplastin. The PT is usually reported as the International Normalised Ratio (INR). 

Administration of zafirlukast and aspirin increases plasma levels of zafirlukast, When zafirlukast is administered with warfarin, there is an increased effect of the anti coagulant. Administration of zafirlukast and theophylline or erythromycin may result in a decreased level of zafirlukast. Administration of montelukast with other drugs has not revealed any adverse responses. Administration of montelukast with aspirin and NSAIDs is avoided in patients with known aspirin sensitivity. Administration of zileuton with propranolol increases the activity or the propranolol with theophylline increases serum theophylline levels and with warfarin may increase prothrombin time (PT). A prothrombin blood test should be done regularly in the event dosages of warfarin need to be decreased. 

Table 32-3 summarizes laboratory results obtained on patients with three different causes of jaundice—hemolytic anemia (a prehepatic cause), hepatitis (a hepatic cause), and obstruction of the common bile duct (a posthepatic cause). Laboratory tests on blood (evaluation of the possibihty of a hemolytic anemia and measurement of prothrombin time) and on semm (eg, electrophoresis of proteins activities of the enzymes ALT, AST, and alkahne phosphatase) are also important in helping to distinguish between prehepatic, hepatic, and posthepatic causes of jaundice. 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Prior to initiating treatment with a LMWH, baseline laboratory tests should include PT (prothrombin time)/INR, aPTT, complete blood cell count (CBC), and serum creatinine. Monitor the CBC every 3 to 4 days during the first 2 weeks of therapy, and every 2 to 4 weeks with extended use.5 Use LMWHs cautiously in patients with renal impairment. Specific dosing recommendations for patients with a creatinine clearance (CrCl) less than 30 mL/minute are currently available for enoxaparin but lacking for other agents of the class (Table 7-3). Current guidelines recommend the use of UFH over LMWH in patients with severe renal dysfunction (CrCl less than 30 mL/minute).8... 

CYP. cytochrome P450 isoenzyme HIV, human immunodeficiency vims INR, International Normalized Ratio LFTs, liver function tests MAOI, monoamine oxidase inhibitor PT, prothrombin time TCA, tricyclic antidepressant. 

TC, lamivudine ABC, abacavir APV, amprenavir AST, aspartate aminotransferase ALT, alanine aminotransferase ATV, atazanavir CBC, complete blood cell count D/C, discontinue ddl, didano-sine d4T, stavudine EFV, efavirenz FTC, emtricitabine P1BV, hepatitis B virus F1CV, hepatitis C vims HIV, human immunodeficiency virus IDV, indinavir IV, intravenous LFT, liver function tests LPV/r, lopinavir + ritonavir NNRTI, nonnucleoside reverse transcriptase inhibitor NRTI, nucleoside reverse transcriptase inhibitor NVP, nevirapine PI, protease inhibitor PT, prothrombin time T.bili, total bilirubin TDF, tenofovir disoproxiI fumarate TPV, tipranavir ULN, upper limit of normal ZDV, zidovudine. 

Prothrombin time (PT) A measure of coagulation representing the amount of time required to form a blood clot after the addition of thromboplastin to the blood sample PT is also known as Quick s test. 

Preanalytical variables that affect global tests for coagulation such as prothrombin time (PT) and activated partial thromboplastin time (APTT) include the choice and concentration of anticoagulant, anticoagulant-to-blQod ratio, pH, concentration of divalent cations, hematocrit, and storage temperature, to mention a few. 

Pruritus, jaundice, palmar erythema, spider angiomata, hyperpigmentation Gynecomastia, reduced libido Ascites, edema, pleural effusion, and respiratory difficulties Malaise, anorexia, and weight loss Encephalopathy Laboratory tests Hypoalbuminemia Elevated prothrombin time Thrombocytopenia Elevated alkaline phosphatase... 

Routine liver assessment tests include alkaline phosphatase, bilirubin, aspartate transaminase, alanine transaminase, and y-glutamyl transpeptidase (GGT). Additional markers of hepatic synthetic activity include albumin and prothrombin time. The substances are typically elevated in chronic inflammatory liver diseases such as hepatitis C, but may be normal in others with resolved infectious processes. 

Current nutritional intake Complete blood cell count Serum electrolytes Sodium Potassium Chloride Bicarbonate Magnesium Phosphorous Calcium Serum glucose Serum albumin Markers for organ function Liver function tests Alkaline phosphatase Aspartate aminotransferase Alanine aminotransferase Total bilirubin Prothrombin time or International normalized ratio Renal function tests Blood urea nitrogen Creatinine Fluid balance Input Oral... 

Liver function tests Alkaline phosphatase Aspartate aminotransferase Alanine aminotransferase Total bilirubin Prothrombin time or International normalized ratio (as necessary)... 

Baseline laboratory tests should include complete blood cell count, prothrombin time, activated partial thromboplastin time, liver and renal function tests, and serum carcinoembryonic antigen (CEA). Serum CEA can serve as a marker for monitoring colorectal cancer response to treatment, but it is too insensitive and nonspecific to be used as a screening test for early-stage colorectal cancer. 

Oral contraceptives have also been reported to produce increases in sulfobromophthalein retention and other liver function tests, as well as in prothrombin time, clotting factors VII, VIII, IX, serum thyroxine, and protein-bound iodine (B8). In a group of 48 women the mean cholesterol value was 206 41 mg/100 ml while they were receiving a variety of oral contraceptives and 179 28 mg/100 ml when they were not receiving the drugs (W19). 

Monitoring Monitor prothrombin time or other suitable anticoagulation test if tigecycline is administered with warfarin. 

Monitoring Monitor renal function frequently during amphotericin B therapy. It is also advisable to monitor liver function, serum electrolytes (particularly magnesium and potassium), blood counts, and hemoglobin concentrations on a regular basis. Use laboratory test results as a guide to subsequent dose adjustments. Monitor complete blood count and prothrombin time as medically indicated. 

Adverse Reactions Diarrhea, nausea Eosinophilia, positive Coombs test, thrombocytosis, agranulocytosis, hemolytic anemia, leukopenia, thrombocytopenia, prolonged prothrombin time Elevation of hepatic enzymes Rash, anaphylactic reaction Phlebitis at injection site... 

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