Technical Strengths and Pitfalls of Serum Tg Measurement

Over the last decade, IMA methodology has largely replaced radioimmunoassays (RIA) for measuring serum Tg concentrations. IMA methods are favored by laboratories because they can be automated and require a shorter incubation to achieve maximal sensitivity, as compared with RIA [9,10]. Current Tg assays suffer from a number of technical limitations that negatively impact their clinical utility. These include (a) large between-method biases that preclude the use of different methods for serial monitoring of DTC patients; (b) suboptimal between-run precision across the long intervals generally used to monitor DTC patients (~12 months) that can mask clinically important changes; (c) inadequate sensitivity that compromises the early detection of recurrence; and (d) interferences by TgAb and

Figure 18.1 Serum Tg concentrations measured in 88 TgAb-negative normal euthyroid volunteers (TSH 0.5-2.5 mlU/L) using different methods. Method #1 = University of Southern California RIA, Los Angeles, CA, USA; method #2 = DSL RIA,Websster,Texas,USA; method #3 = Nichols Advantage ICMA, Nichols Institute Diagnostics ICMA, San Juan Capistrano, CA, USA; method #4 = CIS; method #5 = Access ICMA, Beckman-Coulter, Fullerton, CA, USA; method #6 = Immulite ICMA, Diagnostic Products Corporation, Los Angeles, CA, USA; method #7 = Brahms Kryptor, Berlin, Germany.The shaded area approximates the functional sensitivity. Median values are indicated.

Figure 18.1 Serum Tg concentrations measured in 88 TgAb-negative normal euthyroid volunteers (TSH 0.5-2.5 mlU/L) using different methods. Method #1 = University of Southern California RIA, Los Angeles, CA, USA; method #2 = DSL RIA,Websster,Texas,USA; method #3 = Nichols Advantage ICMA, Nichols Institute Diagnostics ICMA, San Juan Capistrano, CA, USA; method #4 = CIS; method #5 = Access ICMA, Beckman-Coulter, Fullerton, CA, USA; method #6 = Immulite ICMA, Diagnostic Products Corporation, Los Angeles, CA, USA; method #7 = Brahms Kryptor, Berlin, Germany.The shaded area approximates the functional sensitivity. Median values are indicated.

heterophilic antibodies (HAMA) that can lead to the reporting of falsely low or high serum Tg values [7,9,11-13].

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