What is the parameter that is tested to be 13.4? Thyroid function test consists of several parameters, such as TSH, T3, T4, and others. So you should specify what the 13.4 is. If it is TSH, it means that you are hypothyroid and you should increase your levothyroxinine level. If it is T3 or T4, and it is higher than normal, you should instead decrease your levothyroxinine level.