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PubMed1995

Evaluation of a prothrombin time optimized for the dog on plasmas with defined coagulation factor deficiency due to coumarin intoxication.

The sensitivity of the standard prothrombin time (PT) was low when measured on 56 plasmas with a reduced activity of the coagulation factors mainly of the prothrombin complex (factors II, VII and/or X) taken from eight dogs at different times of vitamin K1 therapy after coumarin intoxication. This was demonstrable by use of three different Ca-thromboplastins. With the standard test only plasmas with an excessive decrease of coagulation factor activity (sum of activity decrease of the single factors in relation to the respective reference range [SAD] > 100%) were detectable with sufficient reliability. In contrast, by using a method optimized for dogs (1:20 sample predilution, fibrinogen substitution) and respecting the species specific features of coagulation physiology, pathological PT-values were measured in up to 70% of the samples (dependent on the Ca-thromboplastin) with slight reductions of single factor activity (SAD: 11-25%). Significant differences concerning the sensitivity were seen additionally between the different Ca-thromboplastins. Human placenta thromboplastin in particular, but also rabbit brain thromboplastin, were more sensitive than a preparation of recombinant human tissue factor. The correlation between the PT and the SAD was closer when using the optimized method (r = 0.919-0.954) compared to the standard test (r = 0.771-0.862). In contrast to the standard test, the PT optimized for dogs is, therefore, a reliable screening test to recognize a slight reduction in prothrombin complex. It is especially suitable for monitoring of vitamin K1 therapy after coumarin intoxication.

Animals↗
PubMed2001

Use of EDTA samples for prothrombin time measurement in patients receiving oral anticoagulants.

BACKGROUND AND OBJECTIVES: Oral anticoagulant therapy is commonly called for in health care. Hitherto sampling for prothrombin time (PT) has been measured on blood collected into a coagulation tube and diluted in citrate solution. Blood samples anticoagulated with EDTA are used for hematologic tests and the same sample could also be available for PT. DESIGN AND METHODS: We studied 107 patients on oral anticoagulant therapy. Samples were taken by from both coagulation tubes (citrate) and EDTA tubes. The PT from both samples was measured with an ACL 7000 analyzer and reported in seconds and as an international normalized ratio (INR). The regression equation between citrate and EDTA samples was calculated in both units. We studied the clinical significance of INR results from both sample types and compared the effect of different combined thromboplastin reagents on the correlation equation between citrate and EDTA samples. RESULTS: The regression equation for PT by Owren's PT reagent from citrate (y) and EDTA (x) plasma was y = 1.11 x -0.24 INR, R(2)= 0.99. We observed no clinically significant difference between INR results from citrate and EDTA samples using the regression equation for INR calculation from EDTA samples. ISI depends on sample type (dilution, anticoagulant) and the difference is 0.117, 10%. We calculated ISI for EDTA samples and no clinically significant difference was seen between citrate and EDTA INR results. INTERPRETATION AND CONCLUSIONS: A good correlation was observed between INR results with citrate and EDTA samples from patients receiving oral anticoagulants using Owren's PT reagent with the same citrate calibration. Using the regression equation (INR or sec) for analysis of INR results from EDTA samples is clinically acceptable and offers the possibility of using EDTA samples for PT measurement with citrate calibrators. Reagent international sensitivity index (ISI) values for citrate and EDTA samples differ from each other. ISI determination for EDTA samples requires mathematical calculation of EDTA ISI as in the present study or EDTA-based ISI calibrators. The regression equation for INR from citrate and EDTA samples depended on the reagent used, not only on sample dilution or anticoagulant.

Administration, Oral↗
PubMed2001

[Relationship between prothrombin time international normalized ratio and thrombo test (%)].

OBJECTIVES: The optimal therapeutic range for laboratory evaluation of oral anticoagulant therapy is now defined by the prothrombin time international normalized ratio (PT-INR). However, the thrombo test (TT), an alternative method to measure intensity of anticoagulation, is also currently used throughout Japan. The relationship between PT-INR and TT (%) has yet to be clarified. This study investigated the relationship between PT-INR and TT (%). METHODS: The PT-INR and TT (%) were simultaneously measured of 505 consecutive samples from patients treated with warfarin in our hospital. Fourteen functions were used for regression analyses: a fractional function (Y = a/X + b), a square root function (Y = aX0.5 + b), a natural logarithmic function (Y = a.lnX + b), a power series function (Y = aXb), a quotient function (Y = abX), and polynomial functions [Y = anXn + an - 1Xn - 1 +......+ a1X1 + b, (1 < or = n < or = 9)]. The results were confirmed by the same methods in 383 samples and 296 samples from another two laboratories. RESULTS: The power series function showed the most significant (p < 0.0001) and highest adjusted R2 (0.858) correlation, with a regression formula of TT (%) = e4.48 (PT-INR)-2.09 in our laboratory. Using the same analyses, the power series function also showed the most significant and highest adjusted R2 in samples from the other two laboratories. CONCLUSIONS: This study showed that a power series function is the most appropriate for expressing the relationship between PT-INR and TT (%) among the 14 functions. The function between PT-INR and TT (%) is mainly derived from the relationship between TT (%) and TT (sec). Both internal validity and external validity confirmed the relationship between PT-INR and TT (%).

Aged↗
PubMed2005

The administration of N-acetylcysteine causes a decrease in prothrombin time in patients with paracetamol overdose but without evidence of liver impairment.

OBJECTIVE: To explore the effect of intravenous N-acetylcysteine (NAC) on the prothrombin time (PT) in patients with paracetamol overdose and persistent normal liver profile. MATERIALS AND METHODS: This retrospective case series study examined all admissions with a diagnosis of paracetamol poisoning in a tertiary hospital between 1989 and 2002. Patients were included if they had ever received NAC infusion, had no biochemical evidence of liver damage, and had more than two measurements of PT. Patients who had also ingested other drugs were excluded. RESULTS: Of 65 admissions wtih paracetamol poisoning, 18 patients (10 men) met the inclusion criteria. The median age was 29 years, and the median quantity of paracetamol ingested was 186 mg/kg. The mean number of PT measurements per patient was 4.8. The baseline PT (as a percentage) 8.6 h after paracetamol ingestion was 89.6%. During NAC infusion the PT fell in all patients (range, 4.8-53.4% relative to baseline; P < 0.0001) at 14 h. The PT was less than 60% in 28% of the patients. Eight hours after the initiation of NAC there was a 16% fall in PT (range, 4.3-34%; P < 0.0001). At the end of NAC infusion all PTs returned to values close to baseline. Nine patients were hospitalized. CONCLUSIONS: In patients with paracetamol overdose without evidence of liver damage a marked decrease in PT often occurs, which seems to be due to the overload of NAC infused at the beginning of treatment. This particular feature should be noted in clinical practice guidelines as a potentially misleading indicator of the development of severe liver dysfunction.

Acetaminophen↗
PubMed1980

Prothrombin time standardization and temperature problems.

The reaction temperature is crucial for enzymatic reactions. Difficulties in controlling the temperature in the tilt test tube technique for the prothrombin time test are illustrated. An improved detailed description of the technique is suggested for standardization purposes. Mixing of the specimen with the reagent should be done in the water bath. The test tubes should be immersed deeply into the bath. Recording of the temperature in the reaction mixture is recommended. When using plastic test tubes the temperature problems may be greater than with glass test tubes. Some heat denaturation of coagulation enzymes may take place at 37 degrees C. Lowering the temperature of the reaction to 30 degrees C and perhaps photometric recording of the coagulation should be included in a suggested future optimized reference method.

Evaluation Studies as Topic↗
PubMed1993

Evaluation of a portable prothrombin time monitor for home use by patients who require long-term oral anticoagulant therapy.

BACKGROUND: The anticoagulant activity of warfarin sodium is monitored by the prothrombin time (PT). The introduction of a portable PT monitor has raised the possibility that patients could reduce the inconvenience of anticoagulant therapy by measuring their PT at home. We performed this study to determine the feasibility and accuracy of home use of the portable PT monitor. METHODS: A prospective cohort study was performed in consecutive eligible patients who required long-term anticoagulant therapy. Patients performed multiple measurements of their PT at home by means of the portable monitor and at their usual laboratory within a 4-hour interval. The accuracy of the portable monitor was evaluated by two criteria for agreement. Standard agreement was achieved if the portable monitor and laboratory results were both either within or outside the patient's targeted therapeutic range or if the two results were within 0.4 international normalized ratio units of each other. Expanded agreement was achieved if both the portable monitor and laboratory results were within +/- 0.4 international normalized ratio units of the targeted therapeutic range. RESULTS: Forty patients (19 men and 21 women, aged 25 to 74 years) were followed up for 6 to 24 months by means of the portable PT monitor. The mean level of agreement achieved per patient was 83% (95% confidence interval, 79% to 87%) by the standard criteria and 96% (95% confidence interval, 94% to 98%) by the expanded criteria. Twenty-seven patients (68%) and 39 patients (98%) achieved more than 80% agreement by the standard and the expanded criteria, respectively. Questionnaire results revealed that 97% of the patients preferred using the portable monitor to measure their PT. CONCLUSIONS: Patients receiving long-term anticoagulant therapy achieved a high rate of clinically important agreement between self-measurements of the PT with the use of a portable monitor and laboratory PT results. Patients strongly preferred using the portable monitor to measure their PT levels. The use of the portable monitor as the primary method for measuring the PT can be recommended in selected patients receiving long-term anticoagulant treatment.

Administration, Oral↗
PubMed1995

Complications of warfarin therapy monitored by the International Normalized Ratio versus the prothrombin time ratio.

The objective of our study was to determine the rates of bleeding complications and thromboembolic events in patients receiving oral anticoagulant therapy monitored with the prothrombin time (PT) ratio versus therapy monitored with the International Normalized Ratio (INR) using a retrospective time-series study design. Over 650 patients enrolled in a large anticoagulation clinic were studied during two time periods corresponding to the use of the PT ratio versus the INR to guide anticoagulant therapy, with over 400 patient-years of follow-up for each time period. The rate of bleeding complications using the PT ratio to guide therapy was 6.7% (1.2% major, 5.5% minor) per patient-year, compared with 2.9% (0% major, 2.9% minor) using the INR (p = 0.02). The rate of thromboembolic complications was 1.0% using the PT ratio, compared with 0.2% using the INR (p = NS). Therapy monitored with the INR required 19.8 visits per year, compared with 20.7 visits per year using the PT ratio. We conclude that the INR should be used to monitor oral anticoagulant therapy in an effort to reduce bleeding complications while maintaining an acceptable rate of thromboembolic events.

Drug Monitoring↗
PubMed1994

On-site prothrombin time, activated partial thromboplastin time, and platelet count. A comparison between whole blood and laboratory assays with coagulation factor analysis in patients presenting for cardiac surgery.

BACKGROUND: Although available hemostasis assays from institutional laboratories permit an analytical approach to diagnosis and treatment of coagulation disorders following cardiopulmonary bypass, their clinical utility has been limited by delays in obtaining results. The development of instrumentation for on-site testing allows rapid return of results. This study was designed to compare whole blood (WB) results obtained from on-site coagulation assays with values provided by our institutional laboratory (LAB). METHODS: After Institutional Human Studies Committee approval, 362 patients presenting for cardiac surgery requiring cardiopulmonary bypass were enrolled in this study. Prothrombin time (PT), activated partial thromboplastin time (aPTT), and platelet count (PLT) assays were performed in both WB and LAB systems. PT, aPTT, and PLT measurements were compared between WB and LAB assays using blood specimens obtained from at least two time points for each patient. Normal range values for both PT and aPTT methods were determined by using measurements from a normal reference population. Coagulation factor levels were measured in a subset of patients to characterize the response of PT and aPTT assays to individual and multiple factor levels. To employ Bayes' theorem and calculate predictive indexes (e.g., sensitivity, specificity), the disease or factor deficiency was determined using factor levels. Predictive indexes were used to evaluate the ability of PT and aPTT assays to identify factor deficiency. RESULTS: PLT counts were similar between systems. Linear regression and bias analysis demonstrated similar results for WB and LAB PT and discordant results for aPTT measurements. Both PT assays had a similar normal range, whereas a wider distribution of results was evident for the WB aPTT normal range. Although statistically greater slopes for factor:aPTT regressions were observed for the WB system, WB aPTT correlated better with factor V and with factor V, VIII, and XII levels (multivariate linear regression). Diagnostic performance for factor levels less than 0.3 and 0.4 U/ml was similar for both WB and laboratory PT and aPTT assays. WB and LAB PT and aPTT assays performed similarly in detecting factor deficiency in the period after cardiopulmonary bypass. CONCLUSIONS: WB PT and PLT values correlate well with those obtained from the LAB. The discrepancy between measurement systems in aPTT values is probably a reflection of both different normal ranges and responsiveness to factor deficiency. These WB assays provide coagulation results that can accurately identify patients with quantitative deficiencies in platelets and coagulation factors.

Adult↗
PubMed1992

Recombinant tissue factor as substitute for conventional thromboplastin in the prothrombin time test.

Relipidated recombinant tissue factor (r-TF) has been assessed in comparison with conventional rabbit brain thromboplastin (Manchester Reagent) for its suitability for measurement of prothrombin time (PT). The International Sensitivity Index (ISI) of r-TF calibrated against the International Reference Preparation BCT/253 (human plain) was found to be 0.96 and 1.12 with instrumental and manual techniques. Our study of plasmas from patients with congenital deficiencies of clotting factors covering a wide range of severity demonstrates that r-TF is able to detect even minor deficiencies of factors involved in the extrinsic and common coagulation pathways. Patients with liver diseases were correctly diagnosed with a prevalence of abnormal results comparable for both reagents. Between-assay reproducibility expressed as coefficient of variation was 2.3% and 3.9% at normal and abnormal PT levels. In conclusion, our evaluation shows that relipidated r-TF possesses the necessary requisites of sensitivity, diagnostic accuracy and reproducibility which make it a suitable candidate for PT determination both for monitoring oral anticoagulant therapy and diagnosing congenital and acquired clotting factor deficiencies. Moreover, being a highly defined reagent it may constitute a step forward in the standardization of PT testing.

Anticoagulants↗
PubMed2001

The need for routine pre-operative coagulation screening tests (prothrombin time PT/partial thromboplastin time PTT) for healthy children undergoing elective tonsillectomy and/or adenoidectomy.

In some medical centers, the routine pre-operative evaluation of healthy children undergoing elective tonsillectomy and/or adenoidectomy (T and A) includes coagulation screening tests (PT, prothrombin Time; PTT, partial thromboplastin time; and INR, international normalized ratio). In this retrospective study, we determined whether there is a positive correlation between prolonged PT/PTT/INR tests in healthy children, with no prior medical history of coagulation problems, and bleeding during surgery and/or bleeding in the month following surgery. We reviewed the records of 416 elective T and A surgeries performed at the Soroka University Medical Center in Beer-Sheva, Israel, over the course of 1999. One hundred and twenty-one (29.1%) patients had preoperative prolonged PT values but only four (3.3%) of these patients experienced light bleeding during surgery. Seven (5.8%) of the 121 patients with prolonged PT tests experienced bleeding episodes during the 1st month subsequent to the surgery. Of the 65 (15.6%) patients who had prolonged pre-operative INR values, only three (4.6%) experienced light bleeding during surgery. Two (3.1%) patients with prolonged INR values experienced light bleeding during the 1st month subsequent to surgery. Sixty-one (14.7%) patients had prolonged first preoperative PTT values, only five of whom (8.2%) experienced light bleeding during surgery. Two (3.3%) of the 61 with prolonged PTT values experienced light bleeding during the 1st month subsequent to surgery. We therefore concluded that pre-operative coagulation screening tests provide low sensitivity and low bleeding predictive value. As such, routine coagulation tests before T &A are not indicated unless a medical history of bleeding tendency is suspected.

Adenoidectomy↗
PubMed2001

Evaluation of a point-of-care coagulation analyzer for measurement of prothrombin time, activated partial thromboplastin time, and activated clotting time in dogs.

OBJECTIVE: To evaluate a point-of-care coagulation analyzer (PCCA) in dogs with coagulopathies and healthy dogs. ANIMALS: 27 healthy and 32 diseased dogs with and without evidence of bleeding. PROCEDURE: Prothrombin time (PT), activated partial thromboplastin time (aPTT), and activated clotting time (ACT) were determined, using a PCCA and standard methods. RESULTS: Using the PCCA, mean (+/- SD) PT of citrated whole blood (CWB) from healthy dogs was 14.5+/-1.2 seconds, whereas PT of nonanticoagulated whole blood (NAWB) was 10.4+/-0.5 seconds. Activated partial thromboplastin time using CWB was 86.4+/-6.9 seconds, whereas aPTT was 71.2+/-6.7 seconds using NAWB. Reference ranges for PT and aPTT using CWB were 12.2 to 16.8 seconds and 72.5 to 100.3 seconds, respectively. Activated clotting time in NAWB was 71+/-11.8 seconds. Agreement with standard PT and aPTT methods using citrated plasma was good (overall agreement was 93% for PT and 87.5% for aPTT in CWB). Comparing CWB by the PCCA and conventional coagulation methods using citrated plasma, sensitivity and specificity were 85.7 and 95.5% for PT and 100 and 82.9% for aPTT, respectively. Overall agreement between the PCCA using NAWB and the clinical laboratory was 73% for PT and 88% for aPTT. Using NAWB for the PCCA and citrated plasma for conventional methods, sensitivity and specificity was 85.7 and 68.4% for PT and 86.7 and 88.9% for aPTT, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The PCCA detected intrinsic, extrinsic, and common pathway abnormalities in a similar fashion to clinical laboratory tests.

Animals↗