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Causes and solutions in inadequate thyroid fine needle aspiration samples for reverse transcriptase polymerase chain reaction analysis

Objective: Reverse transcriptase polymerase chain reaction (RT-PCR) is used to detect the expression of different neoplastic markers within samples obtained from thyroid fine needle aspiration (FNA). In most published studies the number of inadequate FNA samples for RT-PCR analysis has not been evaluated. In our study we investigated the causes of inadequate thyroid FNA samples for RT-PCR analysis in attempt to find solutions for better sampling. Materials & Methods: Inadequate FNA samples for RT-PCR analysis were defined as samples with negative GAPDH or Tg gene expression. Thyroid FNA samples of lesions with satisfactory cytological diagnosis other than of follicular cell origin were excluded. A total of 332 samples for RT-PCR analysis obtained by US-guided thyroid FNA were investigated. After the aspirate was smeared for conventional cytology the needle leftover material was used for RT-PCR analysis in 215(65%) cases. In the rest of the cases separate puncture was undertaken to obtain material only for RT-PCR analysis. Nodules were measured in 194(72%) adequate samples, and in 28(44%) inadequate samples. Statistical analysis was performed using chi-square test and Student&#8217; s t-test. P<0.05 was considered significant. Results: In total, 63(19%) inadequate samples for RT-PCR analysis were detected, of which 28(44%) were GAPDH positive but Tg negative. All 10 cases with unsatisfactory cytological diagnosis were in the category of inadequate samples for RT-PCR analysis (P<0.0001). Samples obtained from separate puncture only for RT-PCR analysis were better than those obtained from needle leftover material (P=0.0163). No statistically significant correlation between the nodule size and the number of inadequate samples for RT-PCR analysis was detected. Conclusion: Our results imply a significant number of inadequate thyroid FNA samples for RT-PCR analysis. To decrease this number, we recommend not to continue with RT-PCR procedure on unsatisfactory cytological material. Better sampling is achieved when separate puncture is carried out for RT-PCR analysis.

thyroid nodules; thyroid cancer; fine needle biopsy; reverse transcriptase polymerase chain reaction

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