Interlaboratory Oral Anticoagulant Quality Assessment by the Netherlands Federation of Thrombosis Services

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%).

Photodynamic treatment of pooled coumarin plasma for external quality assessment of the prothrombin time

AIMS

To determine the conditions of photodynamic inactivation of vesicular stomatitis virus (VSV) added to pooled coumarin plasma and the effects of the photodynamic treatment on the prothrombin times and international normalised ratio (INR) in a Netherlands national external quality assessment scheme.

METHODS

Pooled coumarin plasma samples were illuminated with visible light in the presence of 1 microM methylene blue. Inactivation conditions for VSV in pooled coumarin plasma were determined using an end point dilution assay. Plasma illuminated for 20 minutes was mixed with red blood cells and mailed to participants of the Netherlands external quality assessment (EQA) scheme. Prothrombin times and INRs were determined with various thromboplastin reagents.

RESULTS

Photodynamic treatment using 1 microM methylene blue and 700 W/m2 caused 4.7 log inactivation of VSV in pooled coumarin plasma. Fibrinogen and coagulation factors II, V, VII, and X were decreased slightly by the treatment. These conditions caused prolongation of the prothrombin time in EQA surveys. The magnitude of the effect was different for various thromboplastin reagents. The increase of the INR was negligible when measured with the Thrombotest reagent. With other reagents, an approximately 5-16% increase of the INR was observed. Interlaboratory variation of the INR was not affected by photodynamic treatment.

CONCLUSIONS

Photodynamic treatment of pooled coumarin plasma is very effective for the inactivation of some enveloped viruses such as VSV, but has only a limited effect on the prothrombin time and INR. Photodynamic treatment can be used to improve the viral safety of coumarin plasma for EQA of the prothrombin time and INR.

Field study of lyophilised plasmas for local prothrombin time calibration in The Netherlands

AIM

To assess the effect of a lyophilised calibrant plasma procedure on the international normalised ratio (INR) and its interlaboratory variation.

METHODS

INR equivalent values were assigned to five lyophilised plasmas (one from normal donors and four from coumarin treated patients) by a reference laboratory using three calibrated thromboplastin reagents. The calibrant plasmas and five artificial control blood specimens were mailed to 44 Dutch laboratories for prothrombin time (PT) determination. The assigned INR values were used to calculate calibration lines for each participant laboratory. The calibration lines were then used to translate the PT of the control specimens to INR.

RESULTS

For all lyophilised plasmas and control blood samples, there were significant differences between INR values determined with the three thromboplastin reagents. These differences could not be explained by inaccuracy of the international sensitivity index or mean normal PT of the reagents and must, therefore, have been induced by the preparation procedures for the lyophilised plasmas and control blood samples. The interlaboratory variation of the INR obtained with the calibrant plasma procedure had a coefficient of variation (CV) ranging between 2.1% and 7.3% and tended to be lower than the interlaboratory variation found with the usual methods (3.0-12.2% CV). There was a good agreement between the mean INRs obtained with the calibrant procedure and those obtained using the normal methods.

CONCLUSIONS

The present study highlights the limitations of some lyophilised plasmas and control blood samples. It is not possible to assign a single INR value to each of these lyophilised plasmas and control specimens that is valid for all thromboplastin reagents. Nevertheless, by using reagent specific INR equivalent values for the calibrant plasma procedure, the interlaboratory variation could be reduced.

Measured menstrual blood loss in women with a bleeding disorder or using oral anticoagulant therapy

Bleeding disorders in women are associated with a high incidence of menorrhagia, but few objective data exist. Whether oral anticoagulant therapy in women is also associated with a higher incidence of menorrhagia is unknown. We measured menstrual blood loss in six women with various congenital or acquired bleeding disorders and in 11 women treated with oral anticoagulant therapy. Mean menstrual blood loss in women with a bleeding disorder was 219 ml (range, 60 to 568 ml); five women had menorrhagia. In women treated with oral anticoagulant therapy, mean menstrual blood loss was 98 ml (range, 9 to 239 ml), and five women had menorrhagia. Of the six women with normal menstrual blood losses, two had losses in the high normal range (60 to 80 ml). No correlation existed between anticoagulant state and menstrual blood loss. The data support the close association between bleeding disorders and menorrhagia and suggest that oral anticoagulants increase menstrual blood loss.