Thyroglobulin and lactic dehydrogenase isozymes in cystic fluid of thyroid nodules

Although fine needle aspiration biopsy (FNAB) is most valuable in the diagnosis of thyroid cancer, it is hampered by the fact that no specimen suitable for cytological examination can be collected from all cystic lesions. Often inadequate aspirates, consisting only of fluid or a few foamy cells and lacking the necessary epithelial cells, are all that an aspirationist is able to collect. Therefore an alternative method of determining the benign or malignant characteristics of cyst fluid is of vital importance. In this study we examine thyroglobulin (Tg) concentrations and lactic dehydrogenase (LDH) isozyme patterns of cyst fluid and discuss how these variables help us estimate the probability of malignancy. Fifty-three differentiated cancers (39 papillary and 14 follicular carcinomas) and 72 surgically resected benign thyroid nodules (40 adenomas, 19 colloid goiters, and 13 cysts) were analyzed. Only 28 (53%) of 53 malignant lesions were correctly diagnosed by FNAB. The mean logarithmic value for the Tg concentration (log10 Tg) was significantly lower in malignant cyst fluid than it was in benign nodules (mean +/- SD: 5.8 +/- 1.0 vs. 6.8 +/- 1.0; P < 0.001). The LDH 1 and 2 isozyme percentage was greater in the malignant group than in the benign group (49.1 +/- 12.7% vs. 38.1 +/- 16.9%; P < 0.01). In multiple logistic regression analysis, log10 Tg and the total of LDH 1+2 percentage was significant in estimating the probability of malignant nodules. The results of our study suggest that determining the Tg concentration and the LDH isozyme patterns of cyst fluid could provide new information for the evaluation of cystic thyroid nodules.