Summary
In a collaborative trial of eleven laboratories which was performed mainly within
the framework of the European Community Bureau of Reference (BCR), a second reference
material for thromboplastin, rabbit, plain, was calibrated against its predecessor
RBT/79. This second reference material (coded CRM 149R) has a mean International Sensitivity
Index (ISI) of 1.343 with a standard error of the mean of 0.035. The standard error
of the ISI was determined by combination of the standard errors of the ISI of RBT/79
and the slope of the calibration line in this trial.
The BCR reference material for thromboplastin, human, plain (coded BCT/099) was also
included in this trial for assessment of the long-term stability of the relationship
with RBT/79. The results indicated that this relationship has not changed over a period
of 8 years. The interlaboratory variation of the slope of the relationship between
CRM 149R and RBT/79 was significantly lower than the variation of the slope of the
relationship between BCT/099 and RBT/79. In addition to the manual technique, a semi-automatic
coagulometer according to Schnitger & Gross was used to determine prothrombin times
with CRM 149R. The mean ISI of CRM 149R was not affected by replacement of the manual
technique by this particular coagulometer.
Two lyophilized plasmas were included in this trial. The mean slope of relationship
between RBT/79 and CRM 149R based on the two lyophilized plasmas was the same as the
corresponding slope based on fresh plasmas. Tlowever, the mean slope of relationship
between RBT/79 and BCT/099 based on the two lyophilized plasmas was 4.9% higher than
the mean slope based on fresh plasmas. Thus, the use of these lyophilized plasmas
induced a small but significant bias in the slope of relationship between these thromboplastins
of different species.
