Endocrine Abstracts

Background: Indirect methods is developed to estimate reference limits from patient data, i.e. data from a mix of sick and healthy people. The indirect methods use a large number of results. A prerequisite for the methods to work satisfactorily is that the proportion of patients is not too large (typically < 20-30%).

Methods: We used direct and indirect methods for estimating reference limits for TSH, FT4, FT3, total T4 and total T3. All analysis were done with Abbot Alinity. We used was refineR and RefLim in addition to the simple non-parametric percentile method. All patients who have had thyroid parameters analyzed at the Hormone Laboratory in Oslo from December 2021 to June 2023 was included (n=21 539).

Results: We analyzed the thyroid parameters by direct method form 140 healthy participants from the population based HUNT4 study in Norway. In the indirect method we first used our entire database (Hlu, n=21 539). Then a selection were we excluded any sample form hospitals, or were TSH<0.1mIU/l and >10, or positive on anti-TPO or TRAb and only the first measurement of a patient were included (HLc, n=3 366). To validate we included patient sample for the county of Innlandet, Norway, only analyzing samples received from GP`s and only one sample from each patient (IH, n=49 433).

Conclusion: In our Norwegian population it seems like the direct method using healthy individuals form a population based study, is not superior to using indirect methods form our own routine laboratory database.