Summary
In order to study the analytical performance of different commercial kits for determination
of plasminogen activator inhibitor (PAI) activity we distributed eight selected split
samples to 11 European laboratories experienced with haemostasis testing. Three different
laboratories were involved in the production of data from each of the commercial kits
tested. A considerable variation of PAI activity results reported from the laboratories
testing the same commercial kits was observed. The range of reported results could
in individual samples exceed the median value indicating an interlaboratory variation
of more than 100%.
When we harmonized the results reported from different kits in different laboratories
by means of an international standard from National Institute for Biological Standards
and Control (NIBSC) we still observed that the results produced by some kits deviated
systematically from results produced by other kits. Also, the harmonized results were
used to estimate the overall coefficient of variation (CV) of PAI activity determined
in various laboratories by different kits. We observed an inverse correlation between
the PAI activity level and the CV with a CV of about 10Q% for low PAI activity levels
and a CV of about 16% for high PAI activity levels. The high imprecision of the kits
in the low concentration range of PAI activity indicates that unspecific factors in
plasma may interfere with determination of active PAI. This was confirmed by the evaluation
of the results from one of the plasma samples, which was PAI-1 depleted. The laboratories
involved in the testing reported for this sample a mean value of 6.1 IU/ml.
In conclusion, the currently available kits for determination of PAI activity are
not accurate for measurement of PAI-1 in plasma, and the kits give imprecise results
particularly at low activity levels.
