INTRODUCTION. Thyroid nodules are very common and constitute an increasing clinical challenge since improved imaging capabilities and utilisation have led to a higher number of incidental findings. Ultrasoundguided fine-needle aspiration biopsy (FNAB) is the standard diagnostic tool in the work-up of thyroid nodules suspected of malignancy. Non-diagnostic results remain common and require repeated FNAB, leading to increased costs and delayed treatment of thyroid diseases, including treatment of thyroid cancer. If cytological diagnoses cannot be achieved, surgery may be warranted, which may potentially lead to overtreatment. Optimisation of the FNAB procedure is therefore essential. Spinal needles with a stylet have been found to lead to fewer non-diagnostic results, but studies on the subject are few.

METHODS. This is a multicentre, two-arm, randomised clinical trial. Adults with thyroid nodules suspected of malignancy will be included consecutively. A total of 350 patients will be assigned randomly 1:1 to have a FNAB with either a spinal (25G) or a conventional (25G) needle. The primary outcome is the rate of diagnostic cytological samples according to the Bethesda system. Secondary outcomes are patient-experienced pain, complication rate and sensitivity and specificity.

CONCLUSIONS. This trial will explore whether FNAB from thyroid nodules employing spinal needles compared with conventional fine needles improves diagnostic results, thereby providing evidence-based recommendations for a future choice of the FNAB needle. Secondary outcomes are patient-experienced pain, complication rate and sensitivity and specificity.