Rasmussen S.H., Andersen H.H. and Kjelgaard-Hansen M.
This letter is written to raise awareness that there may be no clear benefit in the combined measurement of serum total T4 (tT4) and free T4 (fT4) in dogs and cats suspected of hav- ing hypo- and hyperthyroidism, respectively, in a general clinical setting. The availability of practical automated methods for measuring both tT4 and fT4 (eg, IMMULITE 2000 T41,2 and IMMULITE 2000 free T43) has established these biomarkers as standard analytes in the routine thyroid func- tion profile in dogs and cats. However, as both variables have near-identical diagnostic profiles for general detection of thyroid dysfunction, we were questioning whether combined measurement actually has the potential to contribute significantly to the diagnostic workup of clinical patients by increasing diagnostic accuracy compared with single analyte assessment.