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Clinical Value of a Rapid Fully Automated Thyroid Autoantibody Assay in the Diagnosis and Management of Graves Disease

Original article

Abstrak

Penyebab utama hipertiroidisme adalah Penyakit Grave (GD). Ia merupakan penyakit autoimun dimana berlaku pengikatan antibodi terhadap reseptor hormon perangsang tiroid (TRAb). Tujuan kajian ini adalah untuk memvalidasi pengujian TRAb dari segi kejituan, sensitiviti, spesifisiti dan nilai cut-off. Ujian kejituan (CV) dilakukan secara dalam masa dan sela masa menggunakan dua tahap kawalan kualiti pada julat kepekatan rendah 3.78-7.02 IU/L dan julat kepekatan tinggi 13.5-21.2 IU/L. Untuk menentukan sensitiviti, spesifisiti dan nilai cut-off, 124 sampel serum dari 46 GD , tujuh tiroiditis Hashimoto (HD), 11 goiter nodular non-autoimmune (NAG), dua kanser tiroid and 58 normal sebagai kawalan telah diambil secara retrospektif. Kejituan dalam masa adalah 2.4% pada kepekatan 3.90 IU/L(julat: 3.78-7.02 IU/l) and 0.8% pada kepekatan 20.80 IU/L (julat:13.5-21.2 IU/l). Kejituan keseluruhan adalah 3.8% pada kepekatan 3.80 IU/L (julat:13.5-21.2 IU/l) dan 1.0% pada 20.8 IU/L (julat:13.5-21.2 IU/l). Analisa Receiver-operating characteristic (ROC) menunjukkan sensitiviti terbaik (94%) dan spesifisiti terbaik (98%) adalah pada nilai cut-off 1.69 IU/L. Positive predictive value (PPV) dan negative predictive value (NPV) berada pada 95% dan 94%. Pada nilai 1.69 IU/l ini, didapati sensitiviti untuk 29 sampel pesakit yang baru didiagnosa dengan GD berada pada 94%. Dari kajian ini didapati esai TRAb yang mengambil masa 27 minit ini mempunyai kejituan yang baik, sensitiviti yang tinggi untuk mengesan penyakit GD dan spesifisiti yang bagus untuk membezakan GD dari penyakit tiroid yang lain dan membantu dalam rawatan pesakit tiroid.

Abstract

The most common cause of hyperthyroidism is Graves disease (GD) which is characterised by the presence of autoantibodies which binds to the TSH receptor (TRAb). Recently, a rapid, fully automated electrochemiluminescent immunoassay ElecsysAnti-TSHR for detection of autoantibodies to TSH receptor was made available for routine clinical use. The objective of this study is to evaluate this assay and to determine the sensitivity, specificity and cut-off value. Interassay and total imprecision (CV) were determined at 3.78-7.02 IU/L and 13.5-21.2 IU/L respectively. A total of 124 samples which comprised of 46 GD, seven Hashimoto thyroiditis (HD), 11 non autoimmune nodular goitre (NAG), 2 thyroid cancers (Ca) and 58 normal controls were retrospectively analysed to determine the sensitivity, specificity and cut-off value. Inter-assay CV’s were 2.4% at a concentration of 3.90 IU/L (range: 3.78-7.02 IU/l) and 0.8% at 20.80 IU/L (range:13.5-21.2 IU/l). Total imprecision was 3.8% at a concentration of 3.80 IU/L (range:13.5-21.2 IU/l) and 1.0% at 20.8 IU/L (range:13.5-21.2 IU/l). The ROC analysis of patients with GD, other thyroid disorders and normal controls revealed that the highest sensitivity (94%) and specificity (98%) were seen at cut-off value of 1.69 IU/L. Positive predictive value (PPV) and negative predictive value (NPV) was 95% and 94% respectively. At this derived cut-off value of 1.69 IU/L, we found that the sensitivity of TRAb positivity within the group of 29 newly diagnosed GD patients was 94%. Our results demonstrate that this fully automated assay with testing time of 27 minutes has high sensitivity in detecting GD and high specificity for discriminating other thyroid disease and represent major improvement in the diagnosis and management of patients with thyroid diseases.