T4 (Total Thyroxine)

LABOKLIN Service ID: 137


Material

serum or heparin plasma 0.5 ml resp. 0.4 ml (small mammals)

Method

CLIA

Duration

1 day

Remark

  • Canine: Most frequently used to diagnose hypothyroidism. Caution: A low T4 serum concentration is not necessarily associated with hypothyroidism. TSH is required for further assessment. In addition, rT3 can help differentiate non-thyroidal causes.
  • Monitoring canine hypothyroidism: Blood sampling 4-6 hours after thyroxine administration. Monitor every 2-4 weeks until adequate control of hypothyroidism is achieved. Then every 3-6 months. Aim for a T4 concentration in the middle to upper reference range.
  • Feline: Most frequently used to diagnose hyperthyroidism. Increased T4 serum concentrations indicate hyperthyroidism.
  • Monitoring feline hyperthyroidism: Monitor every 2-4 weeks until euthyroidism is achieved. Then every 3-6 months. Aim for middle reference range. Very low T4 levels should be avoided.
  • Birds and reptiles: Values are physiologically often very low below the detection limit of the test system used); in this case,determination of fT4 is recommended.
  • Horse: If (very rarely occurring) hypothyroidism is suspected, determination of T4 and T3 with a subsequent TRH stimulation test is recommended.