Is there a need to constitute laboratory- and/or region-specific reference ranges for the screening of thyroid disorders?
Dora Horvath1, Erzsebet Toldy2,3, Zoltan Locsei1, Rita Nagy1, Gabor L Kovacs3,5 & Istvan Szabolcs4
Usually, the first laboratory marker for thyroid disorders is TSH. FT4 and FT3 must not be measured unless TSH is out of the reference range. However, the reference range for TSH (and for free thyroid hormones) given by the manufacturers of immunoassays may be not completely valid for screening in iodine-deficient areas and among hospitalized patients either.
Aim: Our aim was to constitute specific TSH, FT4, FT3 reference ranges for the population of our moderately iodine deficient western-Hungarian area, to use them for ambulatory and hospitalized patients by comparing to the manufacturers reference ranges (TSH: 0.44.0 mU/l, FT4: 919, FT3: 2.75.9 pmol/l) to analyze the difference of the number of free hormone estimations needed and also the difference in the expenses.
Methods: To calculate TSH, FT4, and FT3 reference ranges in the disease-free population living in our area, sera of 151 healthy blood donors (without positive personal and familiar thyroid anamnesis) were used. 25 639 thyroid tests on the Architect i2000 analyzer (Abbott) from 14 918 out-patients and 1874 hospitalized patients seen in 2008 were analyzed retrospectively.
Results: In our disease-free population the reference range for TSH is 0.344.32 mU/l, for FT4 9.417.7 and FT3 3.46.3 pmol/l. Among hospitalized patients the reference ranges are wider (TSH: 0.275.9, FT4: 9.621.91, FT3: 1.58.3). By using these reference ranges instead of that of the manufacturers, the need for free hormone tests would have been less by 5082 measurements. (fT4: −1928. fT3: −3158). That would have reduced the expense by 20%, (>4400 € saving per year) without affecting the diagnostic accuracy of the method.
Conclusion: It is well known that the distribution of TSH in the normal population is influenced by the iodine intake. Our results show that is worth and costeffective to use area- and laboratory-specific reference ranges for evaluation of in vitro thyroid tests.