Effect of Needle Gauge on Thyroid FNA Diagnostic Rate

Purpose: Thyroid Bethesda classification system provides 6 diagnostic categories, the first being a sample deemed non-diagnostic or insufficient and requiring a subsequent second biopsy. Our objective was to evaluate differences in non-diagnostic fine needle aspiration (FNA) of thyroid nodules conducted with a 23-gauge(G) needle vs. those conducted with a 25 G needle.

Methods: Data from 298 aspiration procedures using either 23 G or 25 G needles were collected, including cytological findings, ultrasound characteristics and patient demographics. The samples were classified as diagnostic or non-diagnostic according to final cytology.

Results: There was no statistically significant difference between the 25 G and 23 G needles in terms of non-diagnostic rates (35.7%, 31.9%; p = 0.494). Nodules defined as cystic had higher non-diagnostic rates (p < 0.05). Older patients as well as cystic nodules were associated with a higher non-diagnostic rate (OR = 1.018, p = 0.047, OR = 13.533, p = 0.0001, respectively), while nodule size was associated with lower non-diagnostic rates (OR = 0.747, p = 0.017).

Conclusions: The use of 25 G needle did not produce a lower non-diagnostic rate when compared to 23 G needle. Larger nodules might increase diagnostic rates, while older patients and cystic nodules are prone to inadequate samples. Patients and caregivers should be aware that FNA of small or cystic nodules as well as nodules in older patients may result in a higher non-diagnostic rate. Further research comparing other needles gauges should be conducted.