Analytical and diagnostic accuracy of “second generation” assays for thyrotrophin receptor antibodies with radioactive and chemiluminescent tracers

Abstract

Aims: To investigate the analytical and diagnostic accuracy of thyrotrophin (TSH) receptor antibody assays using recombinant human TSH receptors. Methods: Sera from 68 patients with Graves' disease, 23 patients with autoimmune thyroiditis, and 119 healthy controls were evaluated in four different laboratories using both radioactive and chemiluminescent tracers. Functional sensitivity, interlaboratory precision, optimal cutoff values for Graves' disease, and the correlation between the two methods were evaluated. Results: Functional sensitivity was 0.98 IU/litre for both assays. Interlaboratory precision, expressed as per cent coefficient of variation over a wide range of antibody concentrations, varied from 5.7% to 15.1% for the radioligand, and from 6.6% to 19.9% for the chemiluminescence assay. The two methods (radioactive and chemiluminescent) were closely correlated. All the sera from untreated or relapsing patients with Graves' disease gave TSH receptor antibody values above 2.1 IU/litre, whereas in none of the healthy controls did values exceed 2.5 IU/litre. Receiver operating curve analysis allowed an optimal cutoff point to be defined at 1.99 IU/litre, according to a sensitivity of 100% and specificity of 99.1%. Conclusions: These data show the high analytical and diagnostic accuracy of the human TSH receptor assays, both with radioactive and chemiluminescent tracers, when both functional sensitivity and interlaboratory reproducibility are considered. These two methods could be proposed as first line diagnostic markers for Graves' disease.

Accuracy of receptor-based methods for detection of thyrotropin-receptor autoantibodies: a new automated third-generation immunoassay shows higher analytical and clinical sensitivity for the differential diagnosis of hyperthyroidism

“…The aim of the present study was to evaluate the analytical sensitivity and precision and the diagnostic accuracy of a new fully automated system for the measurement of TRAb. Our results clearly show nd not determined that the analytical (functional) sensitivity of the RAD 120 system (0.4 IU/l) was higher than the mean of the secondgeneration (1.4 IU/l) [15,19,22,23], manual third-generation (1.1 IU/l) [26,30] and other automated third-generation assays (0.8 IU/l ) [32,37], probably because of the high analytical precision of the new system (Table 3). Within the last two decades huge efforts have been made to improve the first-generation methods for the measurement of TRAb, based on competitive binding of patients' TRAb and labelled bovine TSH to a soluble porcine TSHR [2].…”

“…The positivity thresholds of these two methods were different from that of the automated method. The Lumitest method showed an optimal threshold value of 1.99 IU/l [23], while the value proposed by the manufacturer (Radim) for the manual third-generation method is 0.4 IU/l. Since comparison data were available only from the GD group, only the 82 GD patients were included in this analysis.…”

“…Several studies have shown that the clinical sensitivity of these assays increases to a mean of 95.9% (range 72.6-100%; Table 1) with a small decrease in specificity (97.9%, range 91.4-100%) [15,[17][18][19][22][23][24][25][26][27][28][29][30]. The recombinant human TSHR-based second-generation assay, in combination with labelled bovine TSH, is now considered the gold standard with the highest diagnostic accuracy.…”

Thyrotropin Isoforms: Implications for Thyrotropin Analysis and Clinical Practice

“…However, in a clinical setting, a physical examination together with biochemical testing can be used to interpret the binding assay results and determine the difference between these effects for a patient. TBII assays have evolved over time (115)(116)(117)(118). The current third-generation assays do not use labeled TSH, but rather human monoclonal thyroid-stimulating immunoglobulins binding to recombinant TSHR.…”

Surgical Management of Hyperthyroidism

“…TSH levels are measured using immunoradiometric and chemiluminescent methods which have a high sensitivity (100%) and specificity (99.1%) [30,31]. When an abnormally low TSH is detected, free Thyroxine (T4) and free Tri-iodothyronine (T3) levels are measured to determine the degree of hyperthyroidism.…”