Prothrombin time

The prothrombin time (PT), as proposed by Quick, is the most commonly performed coagulation function test. It is used to monitor oral anticoagulant therapy and also as a preoperative screening test to warn of possible bleeding risk in patients with a personal or family history of bleeding (Table 36-2). Measured clotting times are extremely dependent on the animal and tissue source and the quality of the thromboplastin used. Variability can be expected because of the assay s dependence on the number of tissue factor molecules and the quantity of 

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The international normalized ratio (INR) is a method to standardize repotting of the prothrombin time, using the formula, INR = (PTpatie t/PTcontroi)ISI, where PT indicates the prothrombin times (for the patient and the laboratory control), and ISI indicates the international sensitivity index, a value that varies, depending upon the thromboplastin reagent and laboratory instrument used to initiate and detect clot formation, respectively. 

Prothrombin time (PT) is a coagulation assay, which measures the time for plasma to clot upon activation by thromboplastin (a mixture of tissue factor and phospholipids). 

Proteosomal Degradation Prothrombin Time Protocadherins Protocidal Drugs... 

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. 

Before administering the first dose of warfarin, die nurse questions the patient about all drags taken during the previous 2 to 3 weeks (if the patient was recendy admitted to the hospital). If the patient took any drug before admission, the nurse notifies the primary healdi care provider before the first dose is administered. Usually, the prothrombin time (PT) is ordered and die international normalized ratio (INR) determined before tiierapy is started. The first dose of warfarin is not given until blood for a baseline PT/ INR is drawn. The dosage is individualized based on die results of the PT or die INR. 

DISPLAY 44-1 Understanding Prothrombin Time and International Normalized Ratio... 

D. checks to see that blood has been drawn for a baseline prothrombin time... 

The nurse monitors the prothrombin time (PT) during therapy. Optimal PT for warfarin therapy is... 

Hematological Effects. Leukocytosis and decreased platelet counts were reported in a group of subjects shortly after they ingested an unknown amount of endosulfan (Blanco-Coronado et al. 1992). One subject from that study, who eventually died, had prolonged partial thromboplastin time and prothrombin time with thrombocytopenia, and decreased fibrinogen two days after being admitted to the hospital. Elevated white cell count was also observed in an additional case of fatal acute poisoning with... 

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. 

Anticoagulant or heparin use <48 h before onset with elevated partial-thromboplastin time Prothrombin time >15 s Platelet count <100,000/mm ... 

Check complete blood count, prothrombin time, international normalization ratio, activated partial thromboplastin time, fibrinogen levels... 

HIT, heparin-induced thrombocytopenia INR, International Normalized Ratio LMWHs, low-molecular-weight heparins PT, prothrombin time UFH, unfractionated heparin. 

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... 

FIGURE 7-9. Initiation of warfarin therapy. INR, International Normalized Ratio PT, prothrombin time. (Reproduced from Haines ST, Zeolla M, Witt DM. Venous thromboembolism. In DiPiro JT, Talbert RL, Yee GC, et al, (eds.) Pharmacotherapy A Pathophysiologic Approach. 6th ed. New York McGraw-Hill 2005 391, with permission.)... 

Prothrombin time (PT) and calculated International Normalized Ratio (INR)... 

Monitor the following serial laboratories for comparison to baseline values every 6 hours in the first 24 hours and daily thereafter until normalized sodium, serum creatinine, blood urea nitrogen, serum lactate, glucose, bilirubin, hemoglobin, hematocrit, platelets, prothrombin time, partial thromboplastin time, arterial blood gases, and pH. 

Elevated prothrombin time (PT) and International Normalized Ratio (INR) are coagulation derangements that indicate loss of synthetic capacity in the liver and correlate with functional loss of hepatocytes. 

ALT, alanine aminotransferase AST, aspartate aminotransferase GGT, gamma-glutamyl transferase INR, international normalized ratio LDH, lactate dehydrogenase PT, prothrombin time. 

Blood urea nitrogen 10 mg/dL (3.6 mmol/L), prothrombin time 12 seconds... 

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. 

Application of topical salicylates can lead to systemic effects, especially if the product is applied liberally. Repeated application and occlusion with a wrap or bandage also can increase systemic concentrations.41 Salicylate-containing counterirritants should be used with caution in patients in whom systemic salicylates are contraindicated, such as patients with severe asthma or aspirin allergy.42 Topical salicylates have been reported to increase prothrombin time in patients on warfarin and should be used with caution in patients on oral anticoagulants.43... 

Prothrombin time PT is performed by adding thromboplastin (tissue) factor and calcium to citrate-anticoagulated plasma, recalcifying the plasma, and measuring the clotting time. The major utility of PT is to measure the activity of the vitamin K-dependent factors II, VII, and X. The PT is used in evaluation of liver disease, to monitor warfarin anticoagulant effect, and to assess vitamin K deficiency. 

Metronidazole Nausea/vomiting Metallic taste Refrain from using alcoholic beverages potential for disulfiram-like reaction Substrate for CYP2C9 and inhibitor of CYP2C9, 3A3/4 and 3A5-7 potential interactions may include warfarin (enhanced prothrombin time) and lithium (increased concentrations)... 

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. 

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