Practical diagnostic utility of thyroid fine-needle aspiration cell blocks: is always too much?

Thyroid fine-needle aspiration (tFNA) is a powerful screening tool for assessing solitary thyroid nodules. Generally, morphologic evaluation of smears yields an accurate diagnosis; but, in some cases it is useful to have a cell block (CB) to conduct ancillary studies such as immunohistochemistry (IHC). Cytologic diagnoses guide clinical decisions, so it is important that accurate and efficient diagnoses be rendered. Our study evaluates the diagnostic utility of the CB in the evaluation of tFNAs.

We performed a retrospective chart review of all tFNA specimens from January 2014 to July 2019. Data collected included TAT (in days), diagnosis, if a CB was prepared, and if it was diagnostically contributory. Descriptive statistics were calculated. Data were analyzed using the χ² test and the Mann-Whitney U-test.

Of the 2321 specimens, 40.2% (933) had CB and only 0.3% (7) were diagnostically contributory. IHC was used for 2 cases. For cases with CB, the median TAT was one day [0-18 days] and the median TAT without CB was 0 [0-9 days]. There was a significant difference in TAT between cases with a CB and those without. Most cases without a CB had same-day TAT (66.4%), whereas only 1.1% of those with a CB had same day TAT. Cases with CB were more likely to have a TAT >1 day (65% versus 12.1%) or >3 days (25.4% versus 10%) than those without a CB (P < 0.0001).

We found the diagnostic utility of CB for tFNAs to be very low. The addition of a CB added at least 1 day to the TAT in all diagnostic strata. The additional time causes patients to wait for results, even for nondiagnostic studies. The increased TAT, resources, and manpower use may be reduced if CB were produced only as needed-if the results of the smear were ambiguous or if ancillary tests were needed to confirm the diagnosis.