Thyroglobulin (Tg)​

Tg must be tested in conjunction TgAB

METHODOLOGY


Immunochemiluminometric assay (ICMA) for Antibody Negative Sera/FNAW
Radioimmunoassay (RIA) for Antibody Positive Sera/FNAW

 

PERFORMED  

IMA: Monday - Friday

RIA: Tuesday - Friday

REPORTED  

 

IMA: 2 dys

RIA: 6 days

COLLECT  

 

One 6mL RT (Min: 4 mL RT)

TRANSPORT  

 

2 mL refrigerated serum or FNAW (Min: 1.0 mL)

STABILITY  

 

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.

UNACCEPTABLE SPECIMENS  

 

The best qualitative result is obtained if the use of grossly hemolyzed or lipemic samples is avoided.

REMARKS

 

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  

 

<1.0 ng/mL

REFERENCE RANGE FOR SERUM 

   

CPT CODE(S)  
 

84432 (Tg)        84432-59 (TGP = concurrent Tg re-measurement of a previous sample)

INTERPRETIVE DATA

 

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.  

USC ENDOCRINE SERVICES LABORATORY
126 W. Del Mar Blvd 
Pasadena, CA 91105-2508
Phone: (855) 224-7111
Fax: (855) 224-7123

Email: endolab@usc.edu

The USC Endocrine Services Laboratory is licensed by the State of California, Department of Health Services, and accredited by the College of American Pathologists, and certified by Medicare according to the provisions of the U.S. Department of Health and Human Services Clinical Laboratory Improvement Act of 1988.

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