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An audit of the reporting of thyroid cytology specimens and their correlation with thyroid histology Anatomical Pathology Laboratory – Groote Schuur Hospital 2016 to 2021
Background: Fine-needle aspiration cytology (FNAC) has been accepted as an effective screening test for patients with thyroid nodules. TBSRTC categorises thyroid FNAC results as non-diagnostic (Category I), benign (Category II), indeterminate (Categories III – V), or malignant (Category VI). Each di...
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| Format: | Thesis |
| Language: | English English |
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Department of Pathology
2026
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| Summary: | Background: Fine-needle aspiration cytology (FNAC) has been accepted as an effective screening test for patients with thyroid nodules. TBSRTC categorises thyroid FNAC results as non-diagnostic (Category I), benign (Category II), indeterminate (Categories III – V), or malignant (Category VI). Each diagnostic category has an estimated risk of malignancy (ROM) based on the literature and is linked to an evidence-based clinical management strategy. Objective: This study evaluates the performance of thyroid FNAC as a screening test for thyroid nodules in our clinical setting. Methods: This is a retrospective laboratory-based study. Reports for all 1 703 thyroid FNAC cases submitted between January 2016 and December 2021 were retrieved from a central data warehouse. We assessed the distribution of cases in each TBSRTC category, performed cytology-to-histology correlation for 315 cases, and calculated the ROM. The diagnostic accuracy, specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Results: The mean proportion of FNAC reports that included a Bethesda category was 74.9%, and 854 (50.1%) cases were non-diagnostic (Category I). The overall ROM, including category I and category II, was 7.4% if cases of low-risk neoplasms were counted as not malignant. The ROM for Categories I to V was within the published TBSRTC ranges, while the ROM for Category VI was slightly lower (81.8% vs 86-100%). The diagnostic accuracy was 54.8%, lower than some published estimates of diagnostic accuracy of 60.2% (20). The specificity was 41.9%, sensitivity was 73.4%, PPV was 46.6%, and NPV was 69.5%. A comparison to published studies showed a wide range of figures, which are influenced by the different methods of calculation used. Conclusion: The rate of non-diagnostic FNACs was higher than published estimates, suggesting the need for ultrasound-guided FNAC with rapid on-site evaluation for specimen adequacy. The ROM for Categories I to V falls within the ranges of studies considered by the TBSRTC guidelines. However, the ROM for Category VI was lower than the ranges of studies considered by the TBSRTC guidelines and other published studies. While we have implemented rapid onsite evaluation for thyroid FNAs performed, there is a need to explore the technical factors that negatively impact FNAC test performance in our setting. What this study adds: To our knowledge, this study analysed the largest cohort of thyroid FNAC cases in South Africa. The study established baseline data on the thyroid cytology-to-histology correlation, the risk of malignancy for each TBSRTC category, and the diagnostic accuracy of thyroid FNAC at a large referral laboratory in South Africa. |
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