A comparison between capillary and venous blood international normalized ratio determinations in a portable prothrombin time device.

The CoaguChek PT system is a portable point-of-care device for prothrombin time testing that can be used with capillary and venous whole blood. This system had been calibrated by the manufacturer in terms of the international normalized ratio (INR) for monitoring oral anticoagulant therapy. The purpose of the present study was to compare capillary blood with venous blood INRs from healthy volunteers and patients treated with oral anticoagulants using the same CoaguChek PT system. Two different CoaguChek PT strip formulations [international sensitivity index (ISI), 1.5 and 1.1] were used in separate test series. The differences between capillary and venous blood INRs were statistically significant (P < 0.001) but the magnitude of the differences was small. The mean relative deviations of the INR were 5.8 and 2.8% for the strips with ISI 1.5 and 1.1, respectively. These deviations are clinically acceptable. It is concluded that capillary blood can be replaced by venous blood for the calibration of the CoaguChek PT system.

Influence of plasma volumetric errors on the prothrombin time ratio and International Sensitivity Index.

The International Sensitivity Index (ISI) for prothrombin time systems depends on the thromboplastin manufacturer's recommended method for use. The purpose of the present study was to investigate the influence of small deviations from the recommended sample volume on the prothrombin time ratio and ISI. Four commercial reagents were studied; three with low ISI and one with high ISI. The effects of volumetric errors on the ISI were used to assess the associated effects on the International Normalized Ratio (INR). The effect of 10% volume error on the INR was not greater than 5%. The effects with the three low-ISI reagents were slightly greater than those with the high-ISI reagent. It is recommended that each laboratory should check the volumes of sample and reagent used for the prothrombin time test.

Preparation of lyophilized partial thromboplastin time reagent composed of synthetic phospholipids: usefulness for monitoring heparin therapy.

To contribute to the development of a reference reagent for monitoring heparin therapy, a lyophilized partial thromboplastin time (PTT) reagent was prepared from synthetic dioleoylphosphatidylcholine, dioleoylphosphatidylserine, and dioleoylphosphatidylethanolamine, with colloidal silica as activator. The reagent, coded 91/558, was contained in sealed glass ampoules; it deteriorated in a heat degradation experiment, but its activity remained constant for at least 4 years when stored at -70 degrees C. Within- and between-run precision with this reagent complied with the requirements proposed by the International Committee for Standardization in Haematology (ICSH) Panel on PTT. The response of this reagent and of two other reagents to heparin added to pooled normal plasma was nonlinear. Citrated samples from 58 patients receiving intravenous heparin and from 24 apparently healthy volunteers were tested with reagent 91/558, with Automated APTT (Organon Teknika), with Manchester APTT reagent, with an antifactor Xa assay, and with an anti-factor IIa assay. The correlation of APTT with anti-Xa and anti-IIa activity was poor. The best correlation was observed between reagent 91/558 and the Organon Teknika reagent. Correlations were improved when individual patients' samples were replaced by pooled plasmas from heparinized patients, in whom the effect of oral anticoagulation was minimal. These results suggest that preparation of a lyophilized synthetic phospholipid reagent is feasible for use in monitoring heparin therapy.

Accelerated degradation test of lyophilized recombinant tissue factor-liposome preparations.

Accelerated degradation experiments were performed to assess the heat stability of lyophilized recombinant tissue factor-liposome preparations from two different manufacturers. When stored at 4 degrees C, these preparations did not show a significant change of the prothrombin time (PT). Two preparations (coded rTF-2 and rTF-a) showed a progressive prolongation of the PT on storage at 30 degrees C, 37 degrees C, and 44 degrees C. The third preparation showed an initial decrease of the PT at 37 degrees C and 44 degrees C followed by a progressive prolongation. Although none of the three preparations was absolutely stable at 30 degrees C, 37 degrees C and 44 degrees C, rTF-2 had the advantage that its PT-ratio (and hence its International Sensitivity Index) did not change under the conditions used in this study. The PT-ratio with a reference material for rabbit brain tissue factor (CRM149S) stored under similar conditions, did not change either.

Enzymatic elimination of heparin from plasma for activated partial thromboplastin time and prothrombin time testing.

The prolongation of the APTT and PT by heparin can be neutralized by treating the plasma with heparinase or with certain anion-exchangers. The purpose of the present study was to assess the effectiveness of a new commercial heparinase reagent. Heparinase (Hepzyme) for the removal of heparin from plasma was compared with ECTEOLA-cellulose treatment. In ex vivo heparin samples, shorter APTT values were obtained with heparinase than with ECTEOLA-cellulose, suggesting that the former treatment is more effective for the removal of heparin from plasma. Heparinase (Hepzyme) treatment may be used to improve INR assessment in patients treated with heparin and oral anticoagulants concomitantly.

Monitoring heparin therapy: relationships between the activated partial thromboplastin time and heparin assays based on ex-vivo heparin samples.

Five different APTT-reagents, two amidolytic anti-IIa assays, one amidolytic anti-Xa assay, and one coagulometric anti-Xa/anti-IIa assay were used to assess the effect of heparin in patients treated for venous thromboembolic disease. Good correlations were observed between log-transformed APTTs determined with the various reagents (correlation coefficients: 0.92-0.96). Nevertheless there were important differences in the slopes of the lines of relationship between the APTT reagents. Good correlations were observed between the anti-Xa and anti-IIa assay results (correlation coefficients: 0.92-0.97). However, the amidolytic anti-Xa activity was significantly higher (p less than 0.001) than the two amidolytic anti-IIa activities. Less good correlations were observed between the log-transformed APTTs and the anti-Xa or anti-IIa activities (correlation coefficients: 0.64-0.78). The correlations were improved by transforming the APTT into APTT-ratio, i.e. the ratio of the patient's APTT to the same patient's APTT after removal of heparin from the plasma sample by means of ECTEOLA-cellulose treatment. The correlation coefficients of log (APTT-ratio) with anti-Xa or anti-IIa ranged from 0.76 to 0.87. For both APTT and amidolytic heparin assay, the response to in vitro heparin was different from the response to ex vivo heparin. Therefore, equivalent therapeutic ranges should be assessed by using ex vivo samples rather than in vitro heparin. Because of the response differences between the APTT reagents, it is not adequate to define a therapeutic range for heparin therapy without specification of the reagent.

Monitoring heparin therapy by the activated partial thromboplastin time--the effect of pre-analytical conditions.

Blood and plasma specimens from patients receiving heparin were collected and stored under various conditions. The effect of these conditions on the activated partial thromboplastin time (APTT) was assessed. Four APTT reagents were used. Blood samples centrifuged at 600 X g gave slightly shorter APTTs than samples centrifuged at 940 X g and 2200 X g. Storage of uncentrifuged citrated-blood at room temperature resulted in 15-29% shortening of the APTT, depending on the reagent used. Storage of the same blood samples at 4 degrees C resulted in 6-19% lengthening of the APTT. The presence of HEPES-buffer in citrated-blood shortened the APTT of heparinized patient specimens, but not of normal specimens. When blood was collected in a mixture of citric acid, theophylline, adenosine and dipyridamole (CTAD-mixture), storage at room temperature induced 0-11% decrease of the APTT, depending on the reagent used. Storage of CTAD-blood at 4 degrees C resulted in 7-19% lengthening of the APTT. Shortening of the APTT could be explained by release of platelet factor 4 (PF4). Release of PF4 could be inhibited by CTAD-mixture. These data suggest that storage of CTAD-blood at room temperature is the best pre-analytical condition for reliable monitoring of heparin therapy by the APTT.