Observer variation in the diagnosis of thyroid disorders. Criteria for and impact on diagnostic decision-making

The thesis is concerned with the reliability of thyroid diagnostic modalities. When no "true" diagnosis was available the reliability could not be evaluated by assessing the accuracy; in these cases the reproducibility was evaluated. This was done by evaluating the observer variation: comparison of observers' evaluation in pairs was assessed. The observer variation was expressed by the kappa coefficient, which adjusts to the amount of agreement that can be expected to occur by chance alone. Clinical estimation only of thyroid functional status was subject to considerable observer variation. Likewise clinical estimation the thyroid gland (size and morphology) was subject to considerable observer variation, and the observer variation was greatest concerning the palpation of a solitary thyroid nodule where even experienced doctors had difficulties in reproducing their own evaluations. In contrast high reproducibility was found concerning the interpretation of routine thyroid blood tests. Thyroid scintigram is not suitable for thyroid size estimation. Assessment of thyroid morphology (diffuse, multinodular, solitary hot or cold lesion) based on scintigram alone seldom resulted in acceptable reproducibility: four doctors diagnosed a solitary cold lesion in 100 of 480 scintigrams, however, they only agreed in 30 of the cases. A solitary cold lesion may in a few per cent of the cases imply malignancy and will therefore lead to further investigations. The reproducibility was not improved when the doctors had additional access to patient history and clinical examination as well as the scintigram. Ultrasound is increasingly often regarded as the "true" diagnosis in the morphological description of the thyroid gland. In a study of two specialists in thyroid ultrasound these descriptions were, however, found not to be reproducible. Thus ultrasound should be applied with caution as the golden standard with regard to thyroid type. It has been demonstrated that thyroid imaging is subject to considerable observer variation. This has great implications when thyroid imaging is used as the golden standard, for example when patients are selected for scientific studies. Furthermore, this may influence the comparison of different studies because of inconsistency of the material included. Therefore the observer variation should appear from description of material and methods in scientific studies. Palpation of thyroid size is neither accurate nor reproducible if an exact volume is aimed at. A rough division into small, medium, and large goitres is reproducible and rather accurate and may therefore be applied. In a prospective randomised study it was demonstrated that this division could replace ultrasound estimation of thyroid size in the calculation of 131I dose in the treatment of hyperthyroidism. Evaluation of thyroid functional status cannot be based on patient history and clinical examination alone, it should include thyroid blood tests. Exact estimation of thyroid size should be performed by means of ultrasound. When morphology of the thyroid is assessed the observer variation should be kept in mind. The existence of observer variation implies uncertainty concerning patient material and inclusion criteria in scientific studies. It may complicate comparison of scientific results. In thyroid diagnostic decision-making doctors should keep in mind that even though there is agreement concerning thyroid blood tests there is not agreement concerning thyroid imaging and the clinical evaluation of patients suspected of thyroid disorders. The patients may experience these disagreements even if the same doctor follows them. Doctors are obliged to use the existing modalities and should be aware of not only problems with technology but also variations originating from the observers, the doctors themselves--the human factor.