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PubMed1988

Survey of prothrombin time in National External Quality Assessment Scheme exercises (1980-87).

National External Quality Assessment Scheme surveys on the prothrombin time test carried out in hospitals in the United Kingdom have been performed at regular intervals since 1972. Performance has been assessed by comparing observed variability between hospitals with that predicted by a statistical model. The model was based on results from 53 survey plasmas issued between 1980 and 1987. These showed a linear correlation between logarithms of mean and standard deviation of reported ratios. Precision improved until the human brain thromboplastin, Manchester Comparative Reagent, was withdrawn in January 1986. There then followed a pronounced overall deterioration which, by October 1987, had not corrected to the levels achieved by 1985. When the recent results from 1986-87 were analysed according to Quick test reagent only one reagent (ISI 1.1) showed an improvement in precision. Performance of the other Quick test reagents, all with higher ISI values, had not regained the standards of precision previously achieved by the human brain reagent.

Animals↗
PubMed1997

Prothrombin time and activated partial thromboplastin time can be performed on the first tube.

The current practice standard for coagulation studies on venous blood specifies the use of the second (or subsequent) tube for testing. Unless other tests are ordered, the first tube is discarded. This practice, derived from early experience using nondisposable materials, gained support from a report based on modern phlebotomy methods but inexperienced phlebotomists. For our study, paired blood specimens were collected by experienced phlebotomists from 175 outpatients whose physicians had ordered coagulation tests. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were performed on the first and second tubes. Similar values were obtained for PT and APTT. (PT: n = 174; mean = 15.36 seconds; mean difference = 0.10 seconds; y = 1.02x - 0.28; t = 0.24; P>.81; r = 0.995; APTT: n = 160; mean = 38.25 seconds; mean difference = 0.48 seconds; y = 1.03x - 0.71; t = 0.25; P=.80; r = 0.993.) For coagulation tests on specimens collected by experienced phlebotomists, the first tube yields accurate results and need not be discarded.

Blood Coagulation Tests↗
PubMed1997

Effect of bezafibrate on hypercoagulability assessed by fluorogenic prothrombin time in hyperlipidemic patients with non-insulin-dependent diabetes mellitus.

We investigated the usefulness of the fluorogenic prothrombin time (FPT) for detection of hypercoagulability and its association with hyperlipidemia in 19 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 10 healthy control subjects, compared with plasma levels of fibrinogen, plasminogen activator inhibitor-1 (PAI-1) and D-dimer. We also evaluated the effect of bezafibrate on hypercoagulability in 10 hyperlipidemic NIDDM patients. The plasma levels of FPT and fibrinogen were significantly higher in hyperlipidemic NIDDM patients than in normolipidemic NIDDM patients and controls. Plasma levels of PAI-1 and D-dimer were significantly higher in normolipidemic and hyperlipidemic NIDDM patients compared with controls. The FPT was correlated with the HbA1c, the body mass index, and levels of total cholesterol, fibrinogen and PAI-1. Six-months therapy with bezafibrate reduced the levels of FPT, triglycerides and basal insulin, but did not alter levels of fibrinogen, PAI-1 and D-dimer. Our results showed that the FPT was useful for detection of hypercoagulability and evaluation of the effect of drugs. The increased FPT in patients with NIDDM suggested that hypercoagulability was present in association with hyperlipidemia.

Aged↗
PubMedDate not supplied

One-stage prothrombin times and subcutaneous haemorrhagic speckling in lambs.

The one-stage prothromhin times of 100 lambs from ten different farms varied from 13 to 24 seconds with a mean of 16.6 seconds. The extent and severity of subcutaneous haemorrhagic speckling of carcases was assessed in 775 animals from the same farms and the prevalence of this lesion was similar to that found at the same works during the 1977/78 season. The means of both one-stage prothrombin times and speckling varied significantly between groups of lambs from different farms but there was no statistical association between the prevalence of speckling and the one-stage prothrombin times.

Journal Article↗
PubMed1994

Low predictive value of an elevated prothrombin time for bleeding on oral anticoagulation.

This study is a retrospective analysis of 39 consecutive patients who had a prothrombin time of over 25 seconds with respect to the bleeding complications. This study finds that the overall risk of bleeding is low, 2/39 (5.1%), that there is no statistical difference in the values of the patients who bled when compared to those who did not, and that patients who bled tended to have a clearly identifiable precipitating event.

Adult↗
PubMed1986

Stability of prothrombin times in sheep dosed with natural and synthetic anticoagulants.

Sheep were dosed with natural and synthetic anticoagulants to prolong prothrombin time (PT) in the one stage PT test. The stability of subsequent values of PT of up to 40 seconds was measured at various times over a 24 hour period in plasma and whole blood stored at 0, 20 and 30 degrees C, representing ideal to unsuitable conditions of sample preparation and storage. In contrast to cautions in the literature, the various treatments had little influence on PT. These findings should encourage the use of PT in field diagnosis and research in sheep by surmounting the tenet of the difficulty in effectively preserving blood samples for PT determinations.

Animals↗
PubMed1979

Quality control trials of prothrombin time: an assessment of the performance in serial studies.

A series of collaborative exercises on the one-stage prothrombin time test involving hospitals in Britain and overseas was performed between 1972 and 1977. The British Comparative Thromboplastin (BCT) and the lyophilised test plasmas were issued from the National (UK) Reference Laboratory for Anticoagulant Reagents and Control. Participants were asked to test the plasma samples with the BCT using the recommended technique. Variability of performance was assessed by the 'index of reliability' based on the plasma variance and error variance within each exercise. The results show that hospitals have attained higher precision in the later trials.

Humans↗
PubMed1996

Prothrombin time sensitivity and specificity to mild clotting factor deficiencies of the extrinsic pathway: evaluation of eight commercial thromboplastins.

Prothrombin-time (PT) sensitivity and specificity to mild clotting factor II, V, VII and X deficiencies have rarely been studied. We therefore carried out a prospective study, in 350 patients, of eight commercial thromboplastins (CTs) in their ability to detect mild clotting factor deficiencies, notably in factor VII. In each patient the factor II, V, VII and X clotting activities and PT performed with each CT were determined. For each CT, PT sensitivity and specificity in detecting factor deficiencies below 0.5 U/ml or below 0.4 U/ml were determined at various PTs, and then Receiver Operator Characteristic curves constructed. At optimum PT threshold level (sensitivity = specificity), exactitude varied from 0.64 to 0.74 (p < 0.01) and from 0.67 to 0.81 (p < 0.0001) in detecting deficiencies below 0.5 and 0.4 U/ml respectively. In conclusion, this study shows the limits of the PT test as performed with 8 CTs in patients with mild clotting factor deficiencies. The impact of such differences in sensitivity and specificity on monitoring certain patients subjects to decrease in coagulation factor, and, in particular, of those under low dose oral anticoagulant, remains to be determined.

Blood Coagulation Disorders↗
PubMed2006

A national field study of quality assessment of CoaguChek point-of-care testing prothrombin time monitors.

A system for quality assessment (QA) of the CoaguChek (Roche Diagnostics, Mannheim, Germany) point-of-care testing prothrombin time monitor has been developed by the European Concerted Action on Anticoagulation. Hitherto there has not been an adequate rapid method for CoaguChek QA. Sets of 5 certified international normalized ratio (INR) plasma samples were tested on 539 CoaguChek monitors by experienced staff at 9 Netherlands Thrombosis Centers and results compared with certified INR. A 15% or more deviation has been classified as significant deviation. Overall mean and certified INR values were similar, but 20.3% of participants showed a 15% or more deviation from the certified INR on at least 1 of the 5 QA plasma samples. Statistically significant differences in results with different lots of CoaguChek test strips were found. There is need for large scale QA of CoaguChek monitors. The importance of the 5 CoaguChek certified INR QA plasma samples being tested on a single occasion is demonstrated.

International Normalized Ratio↗
PubMed1995

Interpretation of serial measurements of international normalized ratio for prothrombin times in monitoring oral anticoagulant therapy.

Despite careful monitoring of oral anticoagulant treatment (OAT), some international normalized ratio (INR) for prothrombin time values will fall outside the therapeutic range. Considerable changes in serial INR results from OAT patients may be caused by random fluctuation alone, and, for statistical reasons, a fraction of the INR values will fall outside therapeutic range and interfere with dose adjustments. On the basis of therapeutic intervals and statistical evaluation of reference changes, we suggest and discuss an alternative method for interpretation of serial INR measurements. Retrospective evaluation of serial measurements of INR from OAT patients revealed an "overshooting" phenomenon. When a dose was adjusted on the basis of insignificant change in INR value, the subsequent INR value generally fell in the opposite direction. If a further change of dose was initiated because of the new INR value, a similar course in the opposite direction was observed. This "ping-pong" effect renders patients in a fluctuating state of anticoagulation and may introduce increased risk of complications. The suggested method provides an objective criterion for dose adjustments in OAT, which should reduce patients' risk.

Anticoagulants↗
PubMed2003

European Concerted Action on Anticoagulation (ECAA). An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors.

AIMS: The recommended method for the international sensitivity index (ISI) calibration of whole blood point of care testing (POCT) prothrombin time (PT) systems was originally described by Tripodi et al in 1993 but is too complex and demanding. The present European Concerted Action on Anticoagulation (ECAA) study aimed to assess the reliability of simpler ISI calibration using lyophilised plasma samples. METHODS: ISI calibrations using three different types of ECAA lyophilised plasma samples (artificially depleted, individual, and pooled coumarin) were compared with whole blood calibrations on CoaguChek Mini and TAS PT-NC POCT monitors at 10 centres. RESULTS: With CoaguChek Mini systems, lyophilised coumarin plasma samples (both single donation and pooled) gave ISI and international normalised ratio (INR) values comparable to whole blood. With artificially depleted plasma, ISI and INR values were too high. With TAS PT-NC systems, all three types of lyophilised plasma samples gave inaccurate ISI and unreliable INR results, similar to previous ECAA findings with fresh plasma calibrations. CONCLUSIONS: With CoaguChek Mini systems, ISI calibration can be simplified by the use of ECAA lyophilised plasma samples from coumarin treated patients. Further study is needed to devise a simpler calibration method for the TAS PT-NC system.

Adult↗
PubMed2003

Agreements between the prothrombin times of blood treated In Vitro with heparinase during cardiopulmonary bypass (CPB) and blood sampled after CPB and systemic protamine.

UNLABELLED: The prothrombin time (PT) is useful for identifying coagulation factor deficits after cardiopulmonary bypass (CPB). However, long processing times and the need for fresh frozen plasma (FFP) to be thawed cause delays in factor replacement. We hypothesized that, by treating with heparinase, blood sampled toward the end of CPB can provide PT results that help to determine the requirement for FFP after CPB. Laboratory delays can be eliminated with point-of-care monitors. We studied 158 adults undergoing nonemergent cardiac surgery. Blood taken before separation from CPB was mixed with heparinase, and PT was measured in the laboratory with a HemoTec timer. Agreements between these results and laboratory measurements of blood taken after systemic protamine were compared by using Bland and Altman plots with the threshold of +/-1.0 s. We found that the laboratory PT measurements during CPB versus after CPB were compara-ble, but the limits of agreement exceeded these thresholds. Similarly, there was unsatisfactory agreement between the HemoTec and laboratory PT results measured before, during, and after CPB. For each PT measured during CPB, the corresponding confidence interval for the postprotamine PT was calculated. During CPB, a laboratory PT of < or =16 s or > or =18 s suggests a > or =83% or > or =93% probability of not requiring or potentially requiring, respectively, FFP after CPB. We conclude that the majority of PT measurements obtained from blood taken before weaning from CPB and treated in vitro with heparinase was associated with a high probability of whether or not FFP would be needed after CPB. IMPLICATIONS: Coagulation dysfunction after cardiopulmonary bypass may contribute to bleeding. Obtaining coagulation tests and fresh frozen plasma requires time and delays treatment in patients who need fresh frozen plasma. We have devised a technique to provide early estimation of postbypass coagulation status.

Aged↗
PubMed1984

Falsely prolonged prothrombin time due to an inhibitor to human thromboplastin.

A patient with nephrotic syndrome of unknown aetiology was found to have a grossly prolonged prothrombin time in the absence of any other coagulation abnormality and with no clinical bleeding problem. Subsequent investigations showed his plasma contained an inhibitor-like substance, directed against human but not animal thromboplastin.

Humans↗
PubMed1985

Reliability and clinical impact of the normalization of the prothrombin times in oral anticoagulant control.

In 1983, the World Health Organization (WHO) published recommendations for normalization, in oral anticoagulant control, of the prothrombin time (PT). The common denominator is the International Sensitivity Index (ISI) of a thromboplastin, obtained by means of thromboplastin calibration. The common scale is that of the International Normalized Ratio (INR). The INR is the PT ratio (Formula: see text) which would have been found with the WHO primary international reference preparation (IRP) 67/40. The reliability of the INR depends on the extent of calibration precision, patient-specific influences, as well as inter-laboratory variation in the PT determination. Under well-controlled conditions the overall coefficient of variation (CV) of the INR is 11-13.5%, if thromboplastins of ISI congruent to 1 are used. For so-called low-sensitivity thromboplastins (ISI congruent to 2-2.5), the overall variation is larger due to a large between-laboratory variation of the measured PT-ratios. The user of thromboplastin will be provided with a chart or graph enabling him to convert the conventional terms used for expressing PTs into INRs. For quality assurance, and to prepare his own calibration chart if necessary, he should check normalization by means of control plasmas to which INRs have been assigned. There is sufficient clinical evidence to express optimal therapeutic ranges in terms of INR. Manufacturers should revise and adapt their inserts where necessary in order to conform to these requirements.

Administration, Oral↗