Differences in serum thyroglobulin measurements by 3 commercial immunoradiometric assay kits and laboratory standardization using Certified Reference Material 457 (CRM-457).

BACKGROUND

Serum thyroglobulin (Tg) is essential in the follow-up of patients with differentiated thyroid carcinoma (DTC). However, interchangeability and standardization between Tg assays have not yet been achieved, even with the development of an international Tg standard (Certified Reference Material 457 [CRM-457]).

METHODS

Serum Tg from 30 DTC patients and serially diluted CRM-457 were measured using 3 different immunoradiometric assays (IRMA-1, IRMA-2, IRMA-3). The intraclass correlation coefficient (ICC) method was used to describe the concordance of each IRMA to CRM-457.

RESULTS

The serum Tg measured by 3 different IRMAs correlated well (r > .85, p < .0001), but clinically relevant discrepancies were found in 13.3% of patients. IRMA-3, which claims to be standardized to CRM-457, showed the best ICC (p(1) = .98) for the CRM-457.

CONCLUSIONS

Hospitals caring for patients with DTC should either set their own cutoffs for IRMAs for Tg based on their patient pools, or adopt IRMAs standardized to CRM-457 and calibrate their laboratory using CRM-457.