Needle washing increases the diagnostic yield of fine needle aspiration biopsy of the thyroid gland.

BACKGROUND AND OBJECTIVE Nodular thyroid disease is a common condition in our clinical practice, and fine needle aspiration biopsy (FNAB) is the diagnostic procedure of choice. Its main limitation is the number of non-diagnostic samples. Since the Bethesda criteria were implemented in 2007 (a consensus document on the morphologic criteria and diagnostic terminology for interpretation of thyroid cytological samples), a higher prevalence of non-diagnostic FNAB was shown. In addition to the standard technique, we decided to collect and centrifuge the material remaining in puncture needles by washing them in a ThinPrep(®) solution, and to assess the increase in the diagnostic yield of FNAB after this change. PATIENTS AND METHODS Systematic sampling of 168 patients who underwent FNAB at the Nutrition and Endocrinology Department of the Xeral-Cies Hospital (Vigo, Spain) from January 2010 to November 2011. Patients were classified into 2 groups: 75 patients in whom the residual material in the needle was not collected (non-washing group) and 93 patients in whom the material was collected (washing-group). All FNABs were performed by the same endocrinologist. Data are shown as percentage (± standard error) for ordinal variables or as mean (± standard deviation) for quantitative variables. A Chi-square test was used for statistical analysis of comparisons between percentages, and a Student's t test for comparisons between quantitative variables. A value of p<0.05 was considered statistically significant. RESULTS No significant differences were found between the groups in age, sex, plasma TSH levels or nodule size. The rate of non-diagnostic FNABs was 44% (± 0.06) in the non-washing group and 17.2% (± 0.04%) in the washing group, with a significant difference (p < 0.01). DISCUSSION Collection and subsequent processing of the residual material in the needle after FNAB significantly decreased the prevalence of non-diagnostic punctures in our patients. Collection of the residual material in the needle in this way is strongly recommended.