Aim: Laboratory results have an important effect on the clinical decision-making process. For this reason, the analysis and reporting quality of the tests is extremely important. Measurement uncertainty is the quantitative expression of the quality of test results. It is also possible to improve the quality of the results by identifying uncertainties and possible sources of errors. The aim of our study is to calculate the uncertainty of total prostate specific antigen (tPSA) and free prostate specific antigen (fPSA) which play an important role in prostate cancer screening and diagnosis tests, according to the Nordest techincal report 537 and comparing these values to the % total allowed error (% TEa) values of The Royal College of Pathologists of Australasia and the Wisconsin State Laboratory of Hygiene (WLSH).

Materials and Methods: fPSA and tPSA tests are analyzed by electro-chemiluminescence method on a Cobas e601 analyzer(Roche Diagnostics GmbH, Mannheim, Germany). The measurement uncertainty of the tests was calculated according to Nordest technical report 537.

Results: The internal quality control uncertainty values of tPSA and fPSA tests are 4.25% and 3.00%, external quality uncertainty values are 5,62 % and 5,83 % and extended uncertainty values are 14,1% and 13,1% (at 95% confidence interval), respectively. TEa value of RCPA for fPSA and tPSA is 15 % and TEa value of WLSH is %30.

Conclusion: The measurement uncertainty calculated for fPSA and tPSA tests in our laboratory is below the targeted %TEa value. Calculation of measurement uncertainty is even more important for tests that assess clinical decision limits in diagnosis and intervention. Clinical laboratories should calculate the measurement uncertainty of tests and the relevant clinicians should be informed about the obtained data.