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PubMed2002

Point-of-care testing for prothrombin time, but not activated partial thromboplastin time, correlates with laboratory methods in patients receiving aprotinin or epsilon-aminocaproic acid while undergoing cardiac surgery.

Point-of-care testing (POCT) of coagulation parameters can help optimize transfusion practice in cardiac surgery. Antifibrinolytic agents may interfere with the laboratory and/or POCT coagulation assays. This randomized controlled study compared coagulation parameters obtained from a whole blood POCT coagulation device with a typical laboratory instrument in cardiac surgery patients receiving aprotinin, epsilon-aminocaproic acid, or normal saline before undergoing cardiopulmonary bypass. Aliquots of arterial blood samples from 42 patients were collected perioperatively, and their prothrombin times (PTs) and activated partial thromboplastin times (aPTTs) were measured by POCT and laboratory instrumentation. Linear regression and error analyses were used for the method comparison. For PT, the POCT device compared favorably with the laboratory method. For aPTT, the POCT device did not compare well with the laboratory method. Treatment with antifibrinolytic agents does not interfere with determination of PT.

Aminocaproic Acid↗
PubMed1997

Comparison of mean normal prothrombin time (PT) with PT of fresh normal pooled plasma or of a lyophilized control plasma (R82A) as denominator to express PT results: collaborative study of the International Federation of Clinical Chemistry. IFCC Working Group Standardization of Coagulation Tests.

The mean normal prothrombin time (MNPT) is currently recommended as the denominator term in the expression of PT ratio or International Normalized Ratio (INR) values. The PT of lyophilized normal control plasmas might also be used in calculating PT ratios, but the overall accuracy of this approach and its dependence on reagents and endpoint detectors have not been evaluated in detail. In an IFCC collaborative study involving 15 expert laboratories and 58 PT systems, the PT ratios of 30 apparently healthy subjects were expressed with the use of the MNPT, the PT of fresh normal pooled plasma (FNPP) obtained from the same apparently healthy subjects, or the PT of plasma R82A--a lyophilized normal pooled plasma prepared by the Verband der Deutschen Geräte-Hersteller for in-house calibration of a large amount of control plasma--as the denominator term. The total imprecision of the PT of plasma R82A averaged 2.16%. Mean PT ratios did not differ from 1.00 (mean 1.00, range 1.00-1.01) with the use of the MNPT as the denominator term. Mean PT ratios were > 1.00 with the FNPP-PT as the denominator term (1.02, 0.96-1.05), and differed according to endpoint detectors (P = 0.024). Mean PT ratios with plasma R82A-PT as the denominator term averaged 0.98 (range 0.91-1.06) with plain thromboplastins (n = 11), 1.02 (0.98-1.06) with combined thromboplastins (n = 3), and 0.93 (0.87-0.97) with recombinant thromboplastins (n = 2), but they differed according to the brand of plain or recombinant reagents (P = 0.00001), the endpoint detector (P < 0.0025), and the plasma citrate concentration (P < 0.0025). These findings underline the differences in the PT of lyophilized plasma R82A and the MNPT and PT of FNPP obtained from the same individuals and support the recommendation that the system-specific MNPT should be used as the ideal index of the normal PT in the calculation of INR values.

Female↗
PubMed1992

Reliance on prothrombin time ratios causes significant errors in anticoagulation therapy.

BACKGROUND: The intensity of warfarin anticoagulation in the United States may be inappropriate if the international normalized ratio (INR) is not used, or if the international sensitivity index (ISI) of the thromboplastin is outside the range of 2.2 to 2.6. METHODS: Fifty-three hospital laboratories provided data on the sensitivity of their thromboplastin and whether they reported INR values. Additional data on thromboplastin sensitivity were obtained from 140 laboratories involved in the Stroke Prevention in Atrial Fibrillation study. The three major manufacturers of thromboplastin confirmed the range of thromboplastin sensitivity reported by the laboratories. RESULTS: Of 53 laboratories surveyed, 16 (30%) could not provide ISI data and only 11 (21%) reported INR results. Unlabeled thromboplastin was being used by 20% to 24% of laboratories, and only 8% to 20% were using thromboplastins with an ISI of 2.2 to 2.6. At the time the three manufacturers were contacted, they reported marketing thromboplastins with ISI values from 1.2 to 2.8, but none of the thromboplastins at that time had ISI values between 2.2 and 2.6. CONCLUSION: Warfarin therapy in the United States is managed inappropriately because most laboratories do not report INRs and the variability in thromboplastin sensitivity produces misleading prothrombin time ratio results. Additionally, recent research may require reexamination if INR or ISI data were not provided.

Data Collection↗
PubMed1994

Use of lyophilized calibration plasmas and control blood for international normalized ratio calculation in external quality assessment of the prothrombin time.

In the Netherlands, most anticoagulant clinics (thrombosis centers) use the reagent Thrombotest with citrated venous blood for laboratory control of oral anticoagulant therapy. In a national external quality assessment scheme, artificial control blood samples were mailed to 160 participants. Each participant returned prothrombin times and international normalized ratio (INR) values for these blood samples. The author investigated whether local calibration with lyophilized plasmas could reduce the interlaboratory variation of the INR. Five lyophilized plasmas were mailed along with the control blood samples. Using a local calibration line determined with the lyophilized plasmas, the interlaboratory variation of INRs determined routinely could be reduced slightly from 5.8% to 7% coefficient of variation (CV) to 5.3% to 6.5% CV. In contrast, when a local calibration line was determined with four similar control blood samples, the interlaboratory variation of the INR was reduced substantially to 2.5% CV.

Calibration↗
PubMed2001

Prothrombin time inhibition detected with recombinant but not with conventional thromboplastins in two patients with high-titre IgM and moderate-titre IgA anticardiolipin antibodies.

We report two cases of high-titre IgM and moderate-titre IgA anticardiolipin antibodies (ACA) in whom prothrombin times (PT) derived using recombinant thromboplastins (rTP) were prolonged but were normal when measured with conventional thromboplastins. The anticoagulant nature of these antibodies cannot be categorized as the classical lupus type. We suggest that routine screening for the presence of antiphospholipid antibodies (APA) should be performed in patients who fall into this category.

Aged↗
PubMed1979

An automated amidolytic assay of thrombin generation: an alternative for the prothrombin-time test.

An automated method is presented for the determination of thrombin generation in plasma during activation by thromboplastin. The thrombin generated is allowed to split the chromogenic substrate Tol-Gly-Pro-Arg-pNA yielding p-nitroaniline. The increase in absorbance at 410 nm is recorded. This assay may serve as a specific, precise and fast alternative for the conventional clotting tests: "Prothrombin time" and "Thrombotest".

Amides↗
PubMed2002

Expression of recombinant rabbit tissue factor in Pichia pastoris, and its application in a prothrombin time reagent.

Tissue factor (TF), or thromboplastin, is a cell membrane-associated glycoprotein composed, in full length, of cytoplasmic, transmembrane, and extracellular domains. It functions as a cofactor in a complex with factor VII (FVII), generating activated factor VII (FVIIa) and initiating blood coagulation. The prothrombin time (PT) assay uses TF as the in vitro activator of coagulation under defined conditions, and it is primarily used to diagnose and manage the extrinsic-pathway factor defficiencies. To overcome the limitations of natural-source TF, we have expressed the mature full-length recombinant rabbit TF (rRTF) protein in Pichia pastoris. Isolation, by purification by immobilized metal-affinity chromatography, of full-length rRTF was facilitated by engineering a (His)(6) tail on its C-terminus, which maximizes the selection of rRTF with intact transmembrane and cytoplasmic domains, critical for proper activity. A PT reagent that incorporates this purified rRTF has performance characteristics similar to those of PT reagents made with natural TF as indicated in method comparison studies, and shows lot-to-lot consistency and reproducibility.

Animals↗
PubMed1994

Implications of use of low international sensitivity index thromboplastins in prothrombin time testing.

The recent introduction of thromboplastin reagents with low international sensitivity index (ISI) values into the US market for the purpose of generating a more precise international normalized ratio than high ISI thromboplastins could has necessitated an evaluation of the impact of the low ISI reagents on prothrombin time (PT) testing in general. In this study, PT testing with three thromboplastin reagents, one of which (presently used in our laboratory) has an ISI of 2.10 and the other two ISI values of 0.92 and 1.06, respectively, was performed on normal individuals, on quality control reference plasma specimens and single-factor-deficient plasma specimens, and on patients with liver disease, intravascular coagulation, and receiving oral anticoagulant therapy. We found that PTs of normal individuals determined by all three thromboplastins were virtually identical. The thromboplastins with a low ISI generated much longer PTs on abnormal reference plasma specimens than did the high ISI product. Low ISI reagents also produced longer PTs in all three groups of patients. However, the degree of prolongation was far greater for patients receiving warfarin than for the other two groups of patients. Conversion of the PT to an international normalized ratio minimized the discrepancy seen in the PT ratio in patients receiving oral anticoagulants. The two low ISI thromboplastins did not produce near-identical values of PT, PT ratio, or international normalized ratio on plasma specimens obtained from patients who received warfarin therapy. The critical value set for PT with a high ISI thromboplastin would not be adequate if the reagent is to be replaced with a low ISI product.

Administration, Oral↗
PubMed2006

Cranberry does not affect prothrombin time in male subjects on warfarin.

There have been case reports suggesting that cranberry beverages may interact with warfarin. To date, no research study has been conducted to examine the potential interaction of cranberry and warfarin. The current study is a randomized, placebo-controlled, double-blind, crossover study to investigate the effect of cranberry juice on prothrombin time as assessed by the international normalized ratio (INR). Seven subjects with atrial fibrillation on a stable dose of warfarin for 3 months were randomized to consume 250 mL of cranberry juice for 7 days, then placebo for 7 days, or vice versa. The washout period was 7 days. The prothrombin time/INR was measured at baseline, and on days 2, 4, 7, 10, 14, 16, 18, 21, and 24. Data were analyzed by the Student t test for paired values. The baseline INR was 2.28+/-0.54 for the cranberry group and 2.13+/-0.50 for the placebo group. For all test points, the INR did not change significantly from baseline. At day 7 on cranberry juice, the INR was 2.23+/-0.53 for cranberry first group and 2.16+/-0.40 for placebo first group. The mean differences between the cranberry and placebo groups were not statistically significant. Our results suggest no significant interaction between the daily consumption of 250 mL cranberry juice and warfarin. When counseling patients on dietary changes necessary during warfarin treatment, it does not seem necessary to eliminate daily cranberry juice consumption at amounts of 250 mL, but the INR should be followed up closely.

Aged↗
PubMedDate not supplied

Effect of intra amniotic saline and prostaglandin on fibrinolytic activity, prothrombin time and serum electrolytes -- a comparative study.

Effects of intra-amniotic instillation of hypertonic saline and prostaglandin F2 alpha for medical termination of pregnancy were studied. Fibrinolytic activity significantly increased at 4 hr and 24 hr after hypertonic saline but only at 24 hrs after prostaglandin. There was no significant change in prothrombin time after hypertonic saline but significant increase was observed after prostaglandin. In both the cases serum sodium level did not show any significant change. Serum potassium level significantly decreased at 24 hrs after hypertonic saline but no change was observed after prostaglandin.

Abortion, Induced↗
PubMed1981

Tentative protocol for the evaluation of coagulometers, based on one-stage prothrombin time.

Information on performance is invaluable to those who have to decide on the choice of an instrument. More interest is being shown in the use of coagulometers. Accordingly, a tentative protocol for the evaluation of coagulometers is presented for discussion. While it is based on the use of one-stage prothrombin time, principles of evaluation are laid down which should make it generally applicable. It is hoped that the tentative protocol will form the basis of a reference protocol and to this end comments are invited from users of coagulometers and suppliers. Comments for publication may be sent to the Editor of Clinical and Laboratory Haematology or to the Secretary of the Working Party.

Blood Coagulation Tests↗
PubMed1990

The dependence of the International Sensitivity Index on the coagulometer used to perform the prothrombin time.

This study was designed to detect any effect that different types of coagulation instrument may have on the International Sensitivity Index (ISI) of a thromboplastin. Manufacturers of commercial thromboplastins now calibrate their reagents against the World Health Organization international reference preparation to assign them an ISI. This enables the prothrombin time (PT) estimated with that reagent to be expressed as an International Normalised Ratio (INR). One batch of Thromborel S was calibrated against the Australasian Reference Thromboplastin (ART). The Thromborel S was used on three photo-optical instruments, the Automated Coagulation Laboratory (ACL) (Instrumentation Laboratory), the Cobas Fibro (Roche), and the Coag-a-Pet (General Diagnostics). PTs using ART were performed manually using the reference method. The ISIs calibrated in our laboratory when the ACL and Cobas Fibro were used were not significantly different at the 95% level, being 1.102 +/- 0.018 and 1.134 +/- 0.022 respectively. The ISI with the Coag-a-Pet of 1.223 +/- 0.023 was significantly different to that of the ACL and the Cobas Fibro at the 95% level. The flowcharts for a computer program to perform the necessary calculations are provided. The program allows for the entry and editing of data from the calibration procedure, and provides a mean normal PT and normal range, the ISI and 95% confidence limits of the calibration, and a chart for the conversion of the test PTs to INRs. The authors have made available an IBM compatible program for the calibration of thromboplastins.

Blood Coagulation Tests↗
PubMed2002

Reliability of point-of-care prothrombin time testing in a community clinic: a randomized crossover comparison with hospital laboratory testing.

The success in achieving therapeutic international normalized ratio (INR) targets in the control of warfarin using a whole-blood point-of-care testing (POCT) monitor (CoaguChek) in a community clinic was compared with hospital laboratory coagulometer prothrombin time (PT) testing in a randomized crossover study. Forty-six patients were randomized into two groups. At each visit, capillary blood was taken for the POCT monitor and venous blood for the laboratory coagulometer. In Group 1, for 6 months, dosage was based on the CoaguChek and for the second 6 months on the coagulometer. In the second group, the order was reversed. Dosages were determined using the dawn ac computer programme. Success was assessed by the percentage of time patients were maintained within the INR targets. Agreement between laboratory and monitor INR, and patient satisfaction were also assessed. Results with the POCT monitor compared well with the hospital coagulometer. Time in INR target range between the groups was similar, with 60.9% on the POCT monitor and 59.3% with the laboratory coagulometer in Group 1 and in Group 2, respectively, 64.3% and 63.4% with no significant difference in mean INR. An INR above 4.0 gave some discrepant results. International Sensitivity Index calibrations of the two test systems indicated that the INRs were dependable. Patient questionnaires showed greater satisfaction with community POCT monitoring.

Anticoagulants↗
PubMedDate not supplied

Reemergence of the International Normalized Ratio for the standardization of prothrombin time.

A survey of physicians demonstrated that half had knowledge of the International Normalized Ratio (INR) but none used the value for monitoring their patients because it was not available from the Coagulation Laboratory. The Laboratory then provided the INR value at a physician's request. A six month review of prothrombin time (PT) results showed that only the physicians from the Cardiology Clinic and the Hematology Clinic employed the INR for monitoring their patients. General Medical and Surgical, Vascular, and Orthopedic Clinics continued to use the PT in seconds. This dichotomy allowed the unique opportunity to compare variability of PT in patients followed by INR and those followed by PT in seconds. Inpatients on daily monitoring were used as the standard for close control. During a six month period, laboratory reports from all patients having regular PTs and/or INRs recorded were analyzed for mean level of PT maintained, variability between individual PTs in any given patient, and instances when the PT changed > or = 5 seconds (sec) or increased to > or = 30 sec. Physicians intended to keep the PTs between 16 and 19 sec (INR 2.0 to 3.0). Results showed statistically significantly lower values of PT, less variation in values of PT and a smaller fraction of patients with changes in PT of > or = 5 sec in the group followed by INR. This group was comparable to the inpatient group but significantly different from the outpatient group followed by PT in sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Monitoring↗