Effect of sampling technique on specimen size in fine needle aspiration biopsy.

The effect of the sampling technique in fine needle aspiration biopsy for cytology (FNAC) on the specimen size obtained was studied in vitro. The specimen size increased rapidly and linearly (P less than .001) with the number of needle passes, if the needle was angled between the passes into different directions in a fan-like fashion. However, if the needle was stroking repeatedly into the same channel, less and less tissue was detached per pass. The effect of the amplitude of needle passes (needle excursion) on the specimen weight was linear (P less than .001) after an initial plateau; when needle excursion was less than 3 to 4 mm, no tissue was detached. The specimen weight was significantly larger when a few passes with long needle excursions were used compared with a large number of passes with small needle excursions. Given an equal number of needle passes, the time interval (frequency) between these passes was less important. The sampling technique is important in determining the size of the specimen. The high incidences of unsatisfactory specimens reported and the wide variation in the accuracy rates of FNAC could be explained partly by differences in sampling techniques.