Value of ancillary studies in fine-needle aspiration biopsy

With growing interest in the application of fine-needle aspiration biopsy (FNAB) in primary diagnosis of benign and malignant lesions, there has been a significant increase in the use of ancillary studies in the aspirated material. To assess the value of such studies, we reviewed 254 morphologically difficult aspiration biopsy cases obtained from different sites that underwent ancillary studies which included microbiology (MC), special stains (SS), immunocytochemistry (ICC), electron microscopy (EM) and flow cytometry (FC). Correlation with available histologic material and/or pertinent clinical information was used as a "gold" standard. In some cases, more than one ancillary study was performed on a single aspirate. According to the impact of the ancillary studies on the final diagnosis, these studies were divided into three categories: confirmatory/diagnostic (22%), helpful (41%), and non-helpful (37%). Overall, more studies had positive contributory effect to the diagnosis (63%) than those with non-helpful results (37%). Among these adjunct testings, ICC were the most commonly used tests (135/296, 46%), while the EM studies had more positive impact in establishing the diagnosis. These findings emphasize the usefulness of ancillary testings in FNAB and justify the more selective use of these studies in the aspirated material.