A modified method of prothrombin time/International Normalised Ratio determination in capillary blood and monitoring oral anticoagulant therapy.
BACKGROUND
Oral anticoagulant therapy is monitored by a prothrombin time (PT) assay. The PT is standardised by the International Normalised Ratio (INR). The purpose of this study was to work out a modified method of PT/INR measurement in capillary blood for monitoring anticoagulation treatment.


METHODS
Healthy donors, subjects with high or low haematocrit values, and oral anticoagulant-treated patients were included in the study. Plasma and capillary blood PT/INRs were determined by the standard Quick clotting assay, by the modified approach and with the CoaguChek S analyser.


RESULTS
The performance characteristics of the developed method were accuracy, due to taking into account whole capillary blood haematocrit values, and precision, due to a decrease in the viscosity of the analysed samples. Implementation of the modified method showed that it is possible to use PT values of normal plasma for capillary blood INR calculation. The developed method allowed the determination of PT in capillary blood within the haematocrit value range from 0.15 up to 0.7. For capillary blood, the results of the modified method closely correlated with PT/INR values determined by the reference Quick method in venous plasma (r=0.99) and with the CoaguChek S analyser (r=0.97).


CONCLUSIONS
The modified method of capillary blood PT/INR determination could be recommended for oral anticoagulant therapy monitoring.
Berkovsky
Aron
A
Institute of Blood Transfusion, Scientific Research Centre of Haematology, Moscow, Russia. aron@blood.ru
Sergeeva
Elena V
EV
Suvorov
Alexander V
AV
Uljavova
Irina S
IS
Kachalova
Natali D
ND
Klimovich
Ljudmila G
LG
Samsonova
Natali N
NN
Kozlov
Albert A
AA
D000284:Administration, Oral; D000925:Anticoagulants / Q000008:administration & dosage; D001777:Blood Coagulation / Q000187:drug effects; D002196:Capillaries / Q000502:physiology; D016903:Drug Monitoring / Q000379:methods* / Q000592:standards; D006400:Hematocrit; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods* / Q000592:standards*; D011517:Prothrombin Time / Q000379:methods* / Q000592:standards*; D012016:Reference Values
D000925:Anticoagulants