Clinical assays are very important for the diagnosis and management of clinical disorders. Each assay system consists of a specific method to detect and/or quantify a substance of interest in the clinical specimen. However, clinical assays can be unfavorably influenced by non-specific activities concomitantly present in the specimen, which may mislead clinical decisions. Thus, it is very important to know how each assay works, and how and when the assay is non-specifically influenced. Here, we report three cases shown clinical data of thyroid function influenced by new type of assay interference.