In feline hyperthyroidism, what is the most commonly used initial screening test?

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Multiple Choice

In feline hyperthyroidism, what is the most commonly used initial screening test?

Measuring serum total T4 (TT4) is the usual first step when screening for feline hyperthyroidism. In most hyperthyroid cats, the overactive thyroid tissue produces more T4, so TT4 levels rise and show up on a standard, widely available test. This makes TT4 a practical, cost-effective screening tool that can quickly confirm the diagnosis in many cases. If TT4 is elevated, that strongly supports hyperthyroidism. If TT4 is normal but clinical suspicion remains high, the next step is often to assess Free T4 by equilibrium dialysis, which is more sensitive and can detect cases that TT4 misses—though it’s more costly and less readily available. T3 concentration isn’t as reliable for screening, and TSH testing isn’t routinely used as an initial screen due to assay limitations and the way TSH behaves in hyperthyroidism.

Measuring serum total T4 (TT4) is the usual first step when screening for feline hyperthyroidism. In most hyperthyroid cats, the overactive thyroid tissue produces more T4, so TT4 levels rise and show up on a standard, widely available test. This makes TT4 a practical, cost-effective screening tool that can quickly confirm the diagnosis in many cases.

If TT4 is elevated, that strongly supports hyperthyroidism. If TT4 is normal but clinical suspicion remains high, the next step is often to assess Free T4 by equilibrium dialysis, which is more sensitive and can detect cases that TT4 misses—though it’s more costly and less readily available. T3 concentration isn’t as reliable for screening, and TSH testing isn’t routinely used as an initial screen due to assay limitations and the way TSH behaves in hyperthyroidism.

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