Long-term stability of relationships between reference materials for thromboplastins

Reference materials for thromboplastins are available from the World Health Organization (WHO) and the European Commission (EC). The long-term stability of the reference materials is an essential requirement and must be monitored. The relationship between two reference materials for rabbit thromboplastin, i.e. ERM-AD 149 (EC) and RBT/90 (WHO), has been monitored in the period 1996-2002. No significant trend with time was detected. In addition, the relationship between ERM-AD 149 and the reference material for bovine thromboplastin (i.e. OBT/79) has been determined in 1994 and in 2005 in multi-centre studies (n = 11 and n = 9, respectively). No significant changes were observed in the relationship between these reference materials when all results were included (5% significance level).