scholarly journals Monitoring Oral Anticoagulant Therapy by the Prothrombin Time: Reporting the Coagulation Activity or the International Normalized Ratio?

1994 ◽  
Vol 24 (1) ◽  
pp. 1-3
Author(s):  
A.M.H.P. van den Besselaar
Keyword(s):  
Prothrombin Time ◽  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Oral Anticoagulant Therapy ◽  
International Normalized Ratio ◽  
Coagulation Activity

scholarly journals Preanalytical Variables and Off-Site Blood Collection: Influences on the Results of the Prothrombin Time/International Normalized Ratio Test and Implications for Monitoring of Oral Anticoagulant Therapy

2005 ◽  
Vol 51 (3) ◽  
pp. 561-568 ◽  
Author(s):  
Johanna HH van Geest-Daalderop ◽  
André B Mulder ◽  
Leandra JM Boonman-de Winter ◽  
Martha MCL Hoekstra ◽  
Anton MHP van den Besselaar
Keyword(s):  
Prothrombin Time ◽  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Room Temperature ◽  
Oral Anticoagulant Therapy ◽  
International Normalized Ratio ◽  
Blood Collection ◽  
Ratio Test ◽  
Mechanical Agitation ◽  
The Impact

Abstract Background: The quality of oral anticoagulant therapy management with coumarin derivatives requires reliable results for the prothrombin time/International Normalized Ratio (PT/INR). We assessed the effect on PT/INR of preanalytical variables, including ones related to off-site blood collection and transportation to a laboratory. Methods: Four laboratories with different combinations of blood collection systems, thromboplastin reagents, and coagulation meters participated. The simulated preanalytical variables included time between blood collection and PT/INR determinations on samples stored at room temperature, at 4–6 °C, and at 37 °C; mechanical agitation at room temperature, at 4–6 °C, and at 37 °C; time between centrifugation and PT/INR determination; and times and temperatures of centrifugation. For variables that affected results, the effect of the variable was classified as moderate when <25% of samples showed a change >10% or as large if >25% of samples showed such a change. Results: During the first 6 h after blood collection, INR changed by >10% in <25% of samples (moderate effect) when blood samples were stored at room temperature, 4–6 °C, or 37 °C with or without mechanical agitation and independent of the time of centrifugation after blood collection. With one combination of materials and preanalytical conditions, a 24-h delay at room temperature or 4–6 °C had a large effect, i.e., changes >10% in >25% of samples. In all laboratories, a 24-h delay at 37 °C or with mechanical agitation had a large effect. We observed no clinically or statistically relevant INR differences among studied centrifugation conditions (centrifugation temperature, 20 °C or no temperature control; centrifugation time, 5 or 10 min). Conclusions: We recommend a maximum of 6 h between blood collection and PT/INR determination. The impact of a 24-h delay should be investigated for each combination of materials and conditions.

Relationship Between Total Prothrombin, Native Prothrombin and the International Normalized Ratio (INR)

1992 ◽  
Vol 68 (02) ◽  
pp. 160-164 ◽  
Author(s):  
P J Braun ◽  
K M Szewczyk
Keyword(s):  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Inverse Relationship ◽  
Low Dose ◽  
Oral Anticoagulant Therapy ◽  
International Normalized Ratio ◽  
Antigen Assay ◽  
Dose Oral ◽  
Anticoagulated Patients ◽  
Sensitive Method

SummaryPlasma levels of total prothrombin and fully-carboxylated (native) prothrombin were compared with results of prothrombin time (PT) assays for patients undergoing oral anticoagulant therapy. Mean concentrations of total and native prothrombin in non-anticoagulated patients were 119 ± 13 µg/ml and 118 ± 22 µg/ml, respectively. In anticoagulated patients, INR values ranged as high as 9, and levels of total prothrombin and native prothrombin decreased with increasing INR to minimum values of 40 µg/ml and 5 µg/ml, respectively. Des-carboxy-prothrombin increased with INR, to a maximum of 60 µg/ml. The strongest correlation was observed between native prothrombin and the reciprocal of the INR (1/INR) (r = 0.89, slope = 122 µg/ml, n = 200). These results indicated that native prothrombin varied over a wider range and was more closely related to INR values than either total or des-carboxy-prothrombin. Levels of native prothrombin were decreased 2-fold from normal levels at INR = 2, indicating that the native prothrombin antigen assay may be a sensitive method for monitoring low-dose oral anticoagulant therapy. The inverse relationship between concentration of native prothrombin and INR may help in identification of appropriate therapeutic ranges for oral anticoagulant therapy.

scholarly journals Comparison of the native prothrombin antigen and the prothrombin time for monitoring oral anticoagulant therapy

Blood ◽  
1984 ◽  
Vol 64 (2) ◽  
pp. 445-451 ◽  
Author(s):  
B Furie ◽  
HA Liebman ◽  
RA Blanchard ◽  
MS Coleman ◽  
SF Kruger ◽  
...  
Keyword(s):  
Prothrombin Time ◽  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Warfarin Therapy ◽  
Oral Anticoagulant Therapy ◽  
Bleeding Complications ◽  
Thromboembolic Complications ◽  
Serum Samples ◽  
Time Index ◽  
Patients At Risk

Abstract We have measured the fully carboxylated (native) prothrombin antigen and the undercarboxylated (abnormal) prothrombin antigen in patients treated with sodium warfarin using specific immunoassays to evaluate a new approach for monitoring oral anticoagulant therapy. Plasma and serum samples (391) were assayed for the prothrombin time, native prothrombin antigen, and abnormal prothrombin antigen. The results were correlated with the presence of bleeding or thromboembolic complications at the time of phlebotomy. The native prothrombin antigen correlated with the occurrence of complications in 95% of samples. Of 13 samples from patients with bleeding complications, 13/13 (100%) had a native prothrombin of 12 micrograms/mL or lower. Of seven samples from patients with thromboembolic complications, 6/7 (86%) had a native prothrombin of 24 micrograms/mL or greater. By comparison, a prothrombin time index of 1.5 to 2.5, 1.5 to 2.2, 1.5 to 2.0, or 1.3 to 1.8 identified 6/20 (30%), 9/20 (45%), 11/20 (55%), or 12/20 (60%) patients at risk, respectively. Although the prothrombin time index did correlate with the presence of bleeding complications, the native prothrombin antigen correlated closely with the presence of bleeding and thromboembolic complications. According to these results, the native prothrombin antigen, maintained in a range of 12 to 24 micrograms/mL by regular adjustment of the warfarin dosage, may be associated with a reduced risk of complications due to excessive or insufficient warfarin therapy. On the basis of these preliminary data, we recommend that the native prothrombin antigen be considered to monitor warfarin therapy.

ASHP therapeutic position statement on the use of the International Normalized Ratio system to monitor oral anticoagulant therapy

1995 ◽  
Vol 52 (5) ◽  
pp. 529-531 ◽  
Keyword(s):  
Clinical Trials ◽  
Patient Outcomes ◽  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Oral Anticoagulant Therapy ◽  
International Normalized Ratio ◽  
Position Statement ◽  
International Agreement ◽  
Warfarin Dosing ◽  
Improve Patient

Summary The INR system of standardizing PT measurements can minimize variability between laboratories, PT reagents, and instruments. The INR system can also facilitate international agreement on therapeutic ranges and allow direct comparison of clinical trials. This should provide greater uniformity in the management of oral anticoagulant therapy and ultimately may improve patient outcomes. ASHP supports the use of the INR system on the basis of studies demonstrating that this system permits warfarin dosing that is less dependent on the variability of thromboplastin reagent sensitivity.

Oral Anticoagulant Therapy Control: Evidence that INR Expression Improves the Inter-Laboratory Comparability of Results - The Bologna Oral Anticoagulant Control Exercise

1987 ◽  
Vol 58 (03) ◽  
pp. 905-910 ◽  
Author(s):  
G Palareti ◽  
S Coccheri ◽  
M Poggi ◽  
M Bonetti ◽  
V Cervi ◽  
...  
Keyword(s):  
Anticoagulant Therapy ◽  
Oral Anticoagulant ◽  
Oral Anticoagulant Therapy ◽  
Normal Subjects ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Therapy Control ◽  
Educational Value ◽  
International Reference ◽  
Interlaboratory Variability

SummaryThe aims of the present study were: l) interlaboratory normalization of prothrombin time (PT) testing for anticoagulant therapy control through calibration of customary thromboplastins against international reference materials, and 2) “on field” validation of the advantages offered by expression of results as International Normalized Ratio (INR) as opposedto percentage activity. PT tests were carried out over 8 days on the same normal subjects (16) and patients on oral an ticoagulants (48) in the 9 laboratories of the Bologna area. The use of customary thromboplastins and coagulometers was maintained in all labs throughout the study. The main results were: 1) the interlaboratory CV of the prothrombin ratios obtained for each sample with all customary thromboplastins (5 different brands) was 15%, but was reduced to levels of 5.8 to 8.9 when using constant thromboplastin brands and batches; 2) the International Sensitivity Index (ISI) values obtained in the different labs were only slightly influenced by the use of different coagulometers; 3) comparable ISI values were obtained through direct calibration with the international reference material and through intermediate calibration with a locally selected standard; 4) use of INR values instead of percentage activity greatly reduced interlaboratory variability and significantly improved uniformity of anticoagulation level measurements. thus reducing the possibility of erroneous prescriptions. The Bologna exercise is therefore of educational value for laboratory and community doctors of the area in understanding and accepting the INR system.

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