Atellica IM Thyroglobulin (Tg)

The Atellica IM Thyroglobulin (Tg) assay is an in vitro diagnostic test that quantitatively measures thyroglobulin in human serum and plasma using the Atellica IM Analyzer. It is intended as an aid in monitoring differentiated thyroid cancer patients who have undergone thyroidectomy with or without radioiodine ablation.

Both the candidate and predicate use chemiluminescent sandwich immunoassays with fully automated operation. The candidate uses mouse monoclonal anti-human Tg antibody labeled with acridinium ester for detection and biotinylated capture antibody on streptavidin-coated paramagnetic particles. Key differences include: candidate assay range 0.050–150 ng/mL versus predicate 0.1–500 ng/mL; candidate requires 100 µL sample versus predicate 40 µL; candidate uses 2 calibration levels versus predicate 6 levels; candidate shows no hook effect up to 80,000 ng/mL versus predicate at least 40,000 ng/mL. Both are standardized to BCR CRM 457.

Performance validated using CLSI protocols: EP17-A2 (detection capability), EP05-A3 (precision and reproducibility), EP06-ed2 (linearity), EP09c-ed3 (specimen equivalence), EP07-ed3 (interference and cross-reactivity), and EP28-A3c (reference intervals). Clinical sensitivity and specificity determined per CLSI EP12-A2.

The assay is substantially equivalent because it employs the same sandwich immunoassay technology and chemiluminescent detection principle as the predicate, measures the same analyte (thyroglobulin) in the same specimen types (serum and plasma), and demonstrates comparable analytical performance with detection limits (LoB 0.039, LoD 0.044, LoQ 0.050 ng/mL) within acceptable ranges of the predicate. Clinical data show 98.2% sensitivity and 99.8% negative predictive value at the 0.2 ng/mL clinical cut-off, supporting equivalent clinical utility for monitoring thyroid cancer patients. Differences in sample volume, calibration levels, and hook effect threshold do not alter the fundamental intended use or clinical purpose.