Evaluation of the Current State of Thyroid Hormone Testing in Human Serum—Results of the Free Thyroxine and Thyrotropin Interlaboratory Comparison Ashley Ribera, Otoe Sugahara, Tatiana Buchannan, Norma Vazquez, Alicia N. Lyle, Li Zhang, Uliana I. Danilenko, and Hubert W. Vesper