Summary
In 4 collaborative trials, involving a varying number of hospital laboratories in
the Stockholm area, the coagulation activity of different test materials was estimated
with the one-stage prothrombin tests routinely used in the laboratories, viz. Normotest, Simplastin-A and Thrombotest. The test materials included different batches
of a lyophilized reference plasma, deep-frozen specimens of diluted and undiluted
normal plasmas, and fresh and deep-frozen specimens from patients on long-term oral
anticoagulant therapy.
Although a close relationship was found between different methods, Simplastin-A gave
consistently lower values than Normotest, the difference being proportional to the
estimated activity. The discrepancy was of about the same magnitude on all the test
materials, and was probably due to a divergence between the manufacturers’ procedures
used to set “normal percentage activity”, as well as to a varying ratio of measured
activity to plasma concentration. The extent of discrepancy may vary with the batch-to-batch
variation of thromboplastin reagents.
The close agreement between results obtained on different test materials suggests
that the investigated reference plasma could be used to calibrate the examined thromboplastin
reagents, and to compare the degree of hypocoagulability estimated by the examined
PIVKA-insensitive thromboplastin reagents.
The assigned coagulation activity of different batches of the reference plasma agreed
closely with experimentally obtained values. The stability of supplied batches was
satisfactory as judged from the reproducibility of repeated measurements. The variability
of test procedures was approximately the same on different test materials.
