Measurement uncertainties and evaluation of test requests in terms of rational laboratory use in tumor markers and thyroid function tests

Aim: This study aimed to identify the inappropriate repeat testing and to evaluate the masurement uncertainties of thyroid function tests (TSH, fT3, fT4), thyroid autoantibodies (Anti-Tg, Anti-TPO), and tumor markers (AFP, CA 125, CA 15-3, CA 19-9, CEA, PSA, fPSA) in accordance with international criteria. Material and Method: The study was conducted using laboratory quality control data and test request data obtained from the hospital information system for the years 2023-2024. Measurement uncertainties were calculated according to the Nordtest approach, and the results were compared with %TEa limits (EFLM, Ricos, CLIA, RiLiBAK, RCPA). Inappropriate repeat tests were determined based on minimum retest intervals and analyzed by gender, age group, admission type, and requesting department. Results: The mean inappropriate repeat rates over two years ranged from 2-13% for tumor markers, 9-19% for thyroid autoantibodies and about 8% for thyroid function tests. Logistic regression analysis revealed that age group, admission type, and department had independent effects on inappropriate retesting (p<0.001). The rate of inappopriate requests was significantly higher in internal medicine departments, inpatients, and patients aged ≥65 years. Measurement uncertainty was highest for thyroid autoantibodies (25-29%), while tumor markers and thyroid function tests showed lower values (8-16% and 9-13%, respectively). Most tests demonstrated acceptable measurement uncertainty according to CLIA and RiLiBAK limits. Conclusion: Regular monitoring of measurement uncertainty supports the reliability of laboratory results and the accuracy of clinical decisions. Requesting tests in accordance with guidelines is essential for patient safety and the efficient use of healthcare resources. Keywords: Measurement uncertainty, rational laboratory use, inappropriate test repetition, thyroid function tests, tumor markers.