Computerized monitoring of potentially interfering medication in thyroid function diagnostics.

Objective: Many drugs are known to affect the results of laboratory tests. This may cause problems in the interpretation of clinical laboratory data and lead to wrong diagnoses, unnecessary further tests and additional costs. A computerized monitoring system of potential drug effects on laboratory tests was developed in Turku University Central Hospital. In the present study the incidence and nature of potentially interfering drug effects in thyroid function diagnostics was examined in order to ease the clinical implementation of the system.

Methods: Computerized medication data of 754 hospital in-patients whose thyroid function was tested were combined with a knowledge base of drug effects on laboratory tests. All medications that potentially affected the levels of serum thyrotropin or free thyroxin in study patients were detected.

Results: 40% (292 of 735) of the patients tested for thyrotropin and 32% (107 of 333) of the patients tested for free thyroxin received potentially interfering medication during the tests. The most common potentially interfering medication was acetylsalicylic acid, but the daily dose was usually low, 100 mg.

Conclusions: The coincidence of potentially interfering medication and thyroid function tests was substantial. On-line hints of drug effects on thyroid function tests might offer valuable decision support to clinicians, but further development of the system is needed to regulate the prevalence of warnings into a clinically optimal level.