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PubMed1999

Standardization of prothrombin time for laboratory control of oral anticoagulant therapy.

Laboratory monitoring of oral anticoagulants is mandatory to ensure efficacy and safety of therapy. The test of choice is the prothrombin time (PT), using thromboplastins, which vary markedly in respect of the defect induced by oral anticoagulants. Standardization is improved by the use of the WHO calibration model for thromboplastins. This system defines the International Sensitivity Index (ISI) of a reagent in relation to a reference material. This is then used together with a locally determined mean normal PT to derive the International Normalized Ratio (INR). There is an inverse relationship between sensitivity and ISI, the lower the ISI the greater is the sensitivity of the reagent. There are important practical advantages to using a sensitive reagent with ISI of 1.2 or less. The ISI system was originally designed for manual tests and in some cases the ISI is influenced by the use of coagulometers, which generally have the effect of lowering the ISI. For this reason the ISI should be assigned for the combination of reagent and endpoint detection system. A thromboplastin should not be used with techniques for which the ISI is unknown. In some instances there is variation between instruments of the same type, in which case a local calibration using plasma calibrants with assigned values can be considered. The precise requirements for such local calibrations are presently the subject of research in a number of centers. The INR/ISI system is increasingly being adopted in many countries for anticoagulant therapy. Some past difficulties leading to discrepancies between results with different reagents have now been resolved and the view that this is the best available system for standardization of the PT for monitoring oral anticoagulants is widely held.

Administration, Oral↗
PubMed2002

Prothrombin time quality assessment scheme in the Basque Country.

The Basque Country Quality Assessment Scheme on Oral Anticoagulant Treatment (PEEC-CAV) was first launched in 1984. This project combined prothrombin time (PT) quality controls and a new in-house standard reagent called Thromboplastin Bilbao (TBi). Originally, this reagent was of human origin, but in 1994, it was replaced by one derived from rabbit brain following WHO recommendations. Nine hospitals in the area collaborated in carrying out quality controls (a) to assess different systems of PT test performance in the Basque Country and (b) to evaluate TBi response in these controls. Evaluation over the period 1994-1999 yielded an INR coefficient of variation (CV) for the plasmas used in these controls of 8.29+/-4.18% using the laboratories' routine system (reagent and coagulometer), and 9.7+/-2.70% using TBi and the manual technique. These results were similar to those obtained in the CV of PT ratio with human brain thromboplastin from 1984 to 1988 (9.26+/-2.84%).

Animals↗
PubMedDate not supplied

Comparative study of a portable prothrombin time monitor employing three different systems in oral anticoagulant units.

The aim of this study was to evaluate the accuracy of the portable coagulometer CoaguChek (Roche Diagnostics) as a prothrombin time (PT) monitor, and to correlate capillary blood results with those of three different routine methods used for monitoring oral anticoagulant therapy (OAT): capillary, plasma and whole blood samples. Three hospitals participated in the study with a total of 235 patients on OAT. The international normalized ratio (INR) results obtained with CoaguChek were compared with those obtained using each of the routine methods. The study presents a good correlation between the PT monitor and the three methods studied: r = 0.9745 (hospital A), r = 0.9283 (hospital B), r = 0.9136 (hospital C). A simplified concordance test of the methods results in a nine-field comparison table showing concordances of 87.2, 85.7 and 68.4%, respectively. The absolute difference (mean +/- SD) between laboratory A and CoaguChek INRs was 0.0571 +/- 0.2042, with values of 0.04286 +/- 0.3906 for laboratory B and 0.6986 +/- 0.6170 for laboratory C. These results confirm that CoaguChek could be used as a new method for oral anticoagulant monitoring, and is in best agreement with the capillary blood PT system.

Humans↗
PubMed1983

Multicentre comparison of nine coagulometers and manual tilt-tube methods for prothrombin time performance.

This multicentre study compares in parallel nine commercial coagulometers and manual tilt-tube methods for their capacity to distinguish two pairs of lyophilized plasmas with slightly different prothrombin times (PTs). The study was based on the rationale that the more precise a method is, the better it is able to discriminate between plasmas with similar PTs. Good or excellent discrimination, as judged by higher Student t values, were achieved slightly more frequently by coagulometers than by manual methods, particularly when paris of plasmas with smaller PT differences were tested.

Anticoagulants↗
PubMed2000

Phytomenadione or menadiol in the management of an elevated international normalized ratio (prothrombin time).

AIM: To evaluate the efficacy of oral menadiol compared to intravenous phytomenadione when correcting coagulopathies associated with cholestasis. METHODS: A total of 26 patients with cholestasis and an international normalized ratio (prothrombin time) greater than 1.2, were randomized to receive either 20 mg o.d. for 3 days of oral menadiol (n=12), or 10 mg o.d. of intravenous phytomenadione (n=14) prior to endoscopic retrograde cholangeopancreatography. Liver function tests and international normalized ratio were measured daily for 3 days. RESULTS: Liver function tests and international normalized ratio were comparable between groups at entry into the study (P > 0.05), but serum albumin was significantly lower in the intravenous phytomenadione group following treatment (P < 0.05). A decrease in international normalized ratio occurred in both groups following administration of vitamin K (P < 0.05). Two patients in the intravenous group required fresh frozen plasma, as failure to normalize international normalized ratio was observed. No adverse drug reactions were observed in either group, and no patient required re-admission for bleeding during a 4-week follow-up period after cholangeopancreatography. CONCLUSION: Oral menadiol appears to be an effective alternative to intravenous phytomenadione in the correction of coagulopathies associated with obstructive liver disease. This simplifies the care of patients with deranged clotting times requiring cholangeopancreatography, particularly those to be managed as out-patients.

Aged↗
PubMed2003

European Concerted Action on Anticoagulation. Correction of displayed international normalized ratio on two point-of-care test whole-blood prothrombin time monitors (CoaguChek Mini and TAS PT-NC) by independent international sensitivity index calibration.

The international normalized ratio (INR) on two widely used point-of-care test (POCT) prothrombin time (PT) monitors (CoaguChek Mini and TAS PT-NC) differed considerably and also differed from the 'true' INR obtained on the same samples using a manual PT and the same species thromboplastin international reference preparation. Agreement between the displayed INR and difference from 'true' INR has been reassessed following an independent international sensitivity index (ISI) calibration of the two systems. The displayed INRs taken at seven centres were compared with 'true' INRs from the same blood donations and INRs based on the resulting ISI. The overall difference between the displayed INRs on the two monitor systems was reduced from 21.0% to 3.5%. The overall difference in mean INR of system A from the 'true' INR was reduced from 19.0% to 9.5% and of system B from 6.8% to 0.3%, but individual centre's results still showed considerable mean INR variability. Differences between overall displayed INR with the two monitor systems have been reduced by an independent multicentre calibration, and agreement with 'true' INR on the same blood samples improved. However, marked variability in mean INR at individual centres remained after ISI correction, which demonstrates the need for external quality control of individual POCT whole-blood PT monitors.

Anticoagulants↗
PubMed1994

French multicentric evaluation of recombinant tissue factor (recombiplastin) for determination of prothrombin time.

Recombiplastin, a recombinant a human tissue factor, elaborated by Ortho Diagnostic Systems, produced by Baculovirus and relipidated with highly purified phospholipids, was tested as a new reagent for determining prothrombin time (PT) in a French multicentric study. Its intralaboratory performances, including sensitivity, repeatability, reproducibility and stability, were explored to establish whether its use would reduce the interlaboratory dispersion of PT values, and therefore improve the standardization of oral anticoagulant treatment. The 9 university hospital hematology laboratories involved in this study used the same type of instrument (KC 10). For 10 consecutive days, they determined PTS on a normal plasma pool, plasma dilutions of 1/2, 1/3 and 1/8, 3 identical lyophilized calibrated plasmas, as well as plasmas from 20 normal subjects, 50 patients on oral anticoagulant therapy with Recombiplastin which has an International Sensitivity Index (ISI) of 1, and 2 commercial thromboplastin extracts (ISI #1 or 2). In the patients on anticoagulants, factors VII, X and V were measured when results were conflicting. The intra and interlaboratory reproducibilities of Recombiplastin, calculated on the basis of either PTS expressed in seconds, or of the International Normalized Ratio (INR), were good, with coefficients of variation (CV) similar to those observed with the 5 other reagents used by the different laboratories (2% < CV < 8%). The stability of Recombiplastin was excellent, with no variation in PT after 72 h of incubation at 37 degrees C. A normal PT of 12 s was obtained with Recombiplastin, similar to the values found for the reagents with ISI #2.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1997

Evaluation of bedside prothrombin time and activated partial thromboplastin time measurement by coagulation analyzer CoaguCheck Plus in various clinical settings.

In the present study CoaguCheck Plus (CCP), a coagulation test system using whole blood, was evaluated with respect to its comparability with widely distributed conventional routine coagulation assays. A correlation of r = 0.997 (p < 0.0001) was found between INR of CCP-prothrombin time (CCP-PT) and Thrombotest (KC-1 analyzer) in patients on oral anticoagulant therapy. A correlation of r = 0.899 (p < 0.001) between CCP-aPTT and Actin ES aPTT (STA analyzer) was found in heparinized patients. Impaired hepatic hepatic coagulation factor synthesis in liver cirrhosis patients was detected by CCP-PT with a sensitivity of 0.75 and by Normotest (STA analyzer) with a sensitivity of 0.92. Those patients with normal CCP-PT values and liver disease had, only mild reductions (> 30% of normals) in coagulation factors II, V, VII or X. CCP-aPTT was also performed in patients with a deficiency in the so called endogenous coagulation factors VIII, IX, XI and XII. CCP-aPTT showed a sensitivity similar to that of Actin FS aPTT in the detection even of mild deficiencies in factors VIII, IX and XII; factor XI deficiency was however detected only in patients with severe (< 12% of normals) disease; lupus anticoagulants were detected with a high sensitivity.

Blood Coagulation Tests↗
PubMed2002

European Concerted Action on Anticoagulation--comparison of fresh plasma and whole blood multicentre ISI calibrations of CoaguChek Mini and TAS PT-NC whole blood prothrombin time point-of-care monitors.

A procedure for using citrated fresh plasmas for International Sensitivity Index (ISI) calibration of two types of whole blood point-of-care test (POCT) prothrombin time (PT) monitor systems has been assessed in a multicentre study. The CoaguChek Mini and TAS PT-NC systems gave higher ISI with whole blood samples than with fresh plasma calibrations. However. there was good agreement between whole blood and fresh plasma monitor system International Normalised Ratio (INR) and the reference INR of target samples. Reliable INR can therefore be obtained with both whole blood and plasma samples on these two POCT systems based on their respective ISI. With the CoaguChek Mini system, the plasma calibration ISI can also be used to derive reliable INR with whole blood PT results. This was not possible with the TAS PT-NC system.

Animals↗
PubMed2002

European Concerted Action on Anticoagulation. Evaluation of a method for International Sensitivity Index calibration of two point-of-care prothrombin time (PT) monitoring systems (CoaguChek Mini and TAS PT-NC) with fresh plasmas based on whole-blood equivalent PT.

BACKGROUND: The International Sensitivity Index (ISI) calibration of whole-blood prothrombin time (PT) monitors for point-of-care testing (POCT) described by Tripodi et al. (Thromb Haemost 1993;70:921-4) has been shown to be dependable but is too complex and demanding. The use of plasma would simplify calibration of whole-blood POCT PT monitors, but important differences may exist between the ISI for whole blood and plasma calibrations. METHODS: In a 10-center calibration study of two POCT whole-blood monitoring systems (CoaguChek Mini and TAS PT-NC), we characterized the relationship between the log PT for whole blood and fresh plasma with use of single lots of test strips/cards. This relationship (linear) was used to correct the difference between the whole-blood and plasma ISI. The reliability of the correction with different lots of test strips/cards was assessed at three centers. The linear relationship was used to correct the difference in the whole-blood and plasma ISI with four other lots of TAS PT-NC cards and with two additional lots of CoaguChek Mini test strips. RESULTS: The correction decreased the ISI difference from 13.3% to 0.9% for the TAS PT-NC and from 5.7% to 0.6% for the CoaguChek Mini. In assessments at three centers, which included different lots of test strips/cards, the mean ISI difference was markedly decreased with the TAS PT-NC but not with the CoaguChek Mini, for which the mean ISI difference increased slightly. CONCLUSIONS: The proposed correction resolves the discrepancy between whole-blood and fresh plasma ISI calibrations with TAS PT-NC test cards. The CoaguChek Mini systems could be calibrated without this correction.

Animals↗