Functional Sensitivity and Dilution for Serum Thyroglobulin Measurement in Differentiated Thyroid Carcinoma

Abstract

There  are  many  factors  that affect  the  performance  of  serum  thyroglobulin  (Tg)

measurement such as functional  sensitivity,  defined as the concentration  that results in a 20% coefficient  of  variation, interference  from  thyroglobulin  autoantibodies (TgAb)  and high Tg level in which appropriate dilution is required. The protocol for serum thyroglobulin measurement is needed for effective laboratory processing. Here, we evaluated functional sensitivity of Tg, TgAb and thyroid stimulating hormone (TSH) according to the National Academy  of  Biochemistry  (NACB)  using  electrochemiluminescence  immunoassay. The functional  sensitivity of Tg, TgAb and TSH were 0.11 ng/mL, 28.3 IU/mL and 0.014  µIU/mL,

respectively. We found 20.9 percent of the 1,426 cases were TgAb-positve when 30 IU/mL were

used as a cut-off level. There was a linearity of Tg level versus undiluted signal until the signal reach at 5,079,926  relative light units (RLU) (r2  = 0.98)  for 343 records. In case of high Tg level, we recommend 1:10 dilution for sample with undiluted signal below 5,000,000  RLU and

1:100  dilution  for  undiluted  signal  above  5,000,000   RLU.  Although  the  Tg  levels  of

1:10 and 1:100 dilutions were significantly different (mean difference = 4.2%) in 45 samples but the values were not exceeding  the total allowable error (TEa of Tg = 21.9%). This study proposed functional sensitivity and dilution protocol for serum thyroglobulin measurement based on the laboratory performance which can be used as a guide or reference source for laboratory services.