Tg must be tested in conjunction TgAB
Immunochemiluminometric assay (ICMA) for Antibody Negative Sera/FNAW
Radioimmunoassay (RIA) for Antibody Positive Sera/FNAW
IMA: Monday - Friday
RIA: Tuesday - Friday
IMA: 2 dys
RIA: 6 days
One 6mL RT (Min: 4 mL RT)
2 mL refrigerated serum or FNAW (Min: 1.0 mL)
Stored at 2 - 8°C until used; Stable if frozen at - 20°C. Studies indicate that Tg in serum is remarkably stable even at ambient temperature if there are no losses due to evaporation. Samples are usually stored at 2 - 8°C for up to one week. For long-term storage, freezing samples at -10 to -20°C is preferred. Repeat thawing and freezing of samples does not influence values if there are no losses due to evaporation.
The best qualitative result is obtained if the use of grossly hemolyzed or lipemic samples is avoided.
The NACB Guidelines state that any laboratory testing for Thyroglobulin MUST also determine the TgAb status of that patient’s sera. The new NACB guidelines also suggest that laboratories archive specimen left after serum Tg measurement for at least 6months. This allows for concurrent re-measurement of the past and current specimens in the same run - a maneuver that eliminates the between-run error and improved the clinical sensitivity of the test. Our lab stores Tg sera indefinitely. *(Thyroid 13:57-67, 2003)
REFERENCE RANGE FOR FNAW
REFERENCE RANGE FOR SERUM
84432 (Tg) 84432-59 (TGP = concurrent Tg re-measurement of a previous sample)
Thyroglobulin (Tg) is routinely measured with a immunochemiluminometric assay (ICMA). Because immunometric assay methodology underestimates serum Tg when TgAb is present, samples with detectable TgAb results are reflexed to the RIA method. (See USC Thyroglobulin Testing Strategy).
The RIA method measures both free and antibody-bound Tg and is minimally affected by TgAb. However, TgAb may interfere and result in falsely low or high Tg levels. TgAb levels may increase after radioiodine treatment and decrease after successful surgery. Total Tg is a useful tumour marker if TgAb levels remain constant.