Biochemical assessment of adequate levothyroxine replacement in primary hypothyroidism differs with different TSH assays: potential clinical implications.

Biochemical assessment of levothyroxine replacement may be dependent on the type of TSH assay. Laboratorians and clinicians should be aware that the lack of harmonisation between TSH methods and their assay-specific reference ranges may potentially lead to different patient management decisions. We suggest lot verification in laboratories should include processes to identify cumulative drift in assay performance.