As pointed out both of them are relatively useless information. Your body ONLY uses FT3.
Measuring FT4 is like determining how well your car runs by looking at the gas level in the fuel tank. Certainly you need gas in the tank in order to run well. But that doesn't mean the engine is operating well even if the tank is full.
Measuring TSH is like measuring the response of the Throttle of the car.
To determine if your engine is running well you need to measure at the very least the fuel flow at the engine and if it is getting enough among other things. That is what FT3 does.
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