Photodynamic treatment of pooled coumarin plasma for external quality assessment of the prothrombin time.
OBJECTIVE
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.
van den Besselaar
A M
AM
Haemostasis and Thrombosis Research Centre, Leiden University Medical Centre, The Netherlands. Abesselaar@hematology.azl.nl
Moor
A C
AC
D003374:Coumarins / Q000097:blood*; D006801:Humans; D007201:Indicator Dilution Techniques; D019934:International Normalized Ratio / Q000592:standards*; D008751:Methylene Blue / Q000494:pharmacology; D010778:Photochemotherapy; D011517:Prothrombin Time; D011785:Quality Assurance, Health Care; D018353:Rhabdoviridae Infections / Q000517:prevention & control; D014721:Vesicular stomatitis Indiana virus / Q000187:drug effects*; D014775:Virus Activation / Q000187:drug effects
D003374:Coumarins; D008751:Methylene Blue