Objective: In the clinical laboratories, the same test could be analyzed by more than one assay system or analyzer due to various requirements. This may cause a problem in patient monitoring. In our laboratory, stat TSH testing has been recently implemented in the stat biochemistry laboratory for meet emergency request meanwhile routin analyses have been carried out in the endocrine laboratory. This study was aimed to investigate the concordance between test results generated by different asssay systems or analyzers, and to define whether the differences are in the acceptable limits or not.

Materials and Methods: Fifthy three sera remaining from the routine analyses were used for the method comparison study; of which TSH concentrations ranged from 0.029 µIU/ml to 165.0 µIU/ml. After analyzed by Siemens Immulite 2000 XPi (instrument 1) in the endocrine laboratory, the samples were analyzed by the other Siemens Immulite 2000 XPi (instrument 2) in the endocrine laboratory and the Abbott Architect i2000 at the stat biochemistry laboratory on the same day. The concordance between the results were evaluated by a regression analysis and Bland-Altman graphics by means of MedCalc statistics software.

Results: Strong correlations between the TSH results obtained from the three analyzers were obtained; the systematic difference between Siemens Immulite 2000 XPi analyzers was 4.7%, and the systematic difference between Siemens Immulite 2000 XPi (instrument 1)-Abbott Architect i2000 was 22.8%, and finally it was 23.1% between Siemens Immulite 2000 XPi (instrument 2)-Abbott Architect i2000. The TSH results generated by Abbott Architect i2000 were lower then those generated by Siemens Immulite 2000 XPi.

Conclusion: Due to the high systematic diferences, higher than total allowable error, obtained between Abbott Arhitect and Siemens Imulite systems, we assume the use of two diferrent systems at the same time for the same test may cause problems in patientsÕ monitoring. If the use of two different system at the same time is obligatory, clinicians should be informed about this situation. The name of the analyzer or the system which generates the results should be involved on the laboratory reports. In addition, our findings demonstrated that in case of a new method to be used in the laboratory, there is a need for a comparison to the already existing method by means of patient based samples and also for a standardization between methods.