Thin layer compared to direct smear in thyroid fine needle aspiration

The efficacy of preparing thyroid fine needle aspirations (FNAs) by the thi n layer as opposed to the direct smear method has not been evaluated suffic iently in a regional laboratory setting. At the Foothills Hospital (Calgary , Canada), the method of processing thyroid FNAs was changed from direct sm ear to thin layer in January 1996. The results of 327 patients who had dire ct smear from 1994 to 1995 were compared to 401 who had thin layer between 1996 and 1997. While there were no significant differences across a broad r ange of quality indicators, thin layer showed a trend towards a higher prop ortion of true benign diagnoses (31% vs 24%), a lower proportion of inadequ ate specimens (41% vs 50%) and, most importantly, a lower false negative ra te (3% vs 9%). In conclusion, the changeover to thin layer did not compromi se the interpretation of thyroid FNAs.