Purpose: A parameter associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed to the measurand is defined as measurement uncertainty (U). Measurement uncertainty is very important for the clinician to provide medical judgement, diagnosis and treatment. The aim of this study was to determine the measurement uncertainty of fT4, fT3 and TSH parameters in our laboratory.

Material and Methods: In this study, measurement uncertainty calculation was done using Nordtest guide model. Standard, combined and expanded uncertainty values were calculated with this model.

Results: Expanded uncertainty was calculated 17.93% for TSH. We found measurement uncertainty of fT4 and fT3 were % 8.83 and %9.13, respectively. Expanded uncertainty of fT4 was found to be higher when compared to %TEa values of Westgard.

Conclusion: All changes may affect the uncertainty in the laboratory. Therefore, it must be constantly monitored and uncertainty estimates should be improved by adding more data.