Week-to-week variation of scintigraphic (semi-)quantitative thyroid variables in 14 healthy experimental cats

Although scintigraphy is an important tool for the assessment of thyroid function in cats, time variation of commonly used thyroid variables has not been investigated to this day. The aim of this study was to investigate whether a week-to-week variation of scintigraphic variables exists in healthy cats of a magnitude that is clinically relevant, as this could lead to misinterpretation of results. Fourteen adult, healthy, experimental cats were included in the study. At 3 time points, with 7-day intervals, the cats underwent a thyroid pertechnetate scan and blood samples were collected. The scintigraphic variables calculated were the thyroid to salivary gland ratio (T/S), thyroid to background ratio (T/B), percentage technetium uptake in the thyroid glands (%TcU_T) and additionally percentage technetium uptake in the salivary glands (%TcU_SG). Two thyroid hormones, total thyroxine (TT₄) and thyroid stimulating hormone (TSH), were included in the analysis. All scintigraphic variables, with the exception of the %TcU_T and T/B_neck ratio, were within the normal reference ranges reported in literature. No clinically relevant week-to-week variation was observed for any of the variables included in this study.