Pathology/Lab Coding Alert

Question: What ICD-10 code would you use for a thyroid FNA of a nodule that has the final diagnosis of “follicular lesion of undetermined significance”?

Missouri Subscriber

Answer: The correct ICD-10 code is D44.0 (Neoplasm of uncertain behavior of thyroid gland).

The terminology you found in the pathology report, “follicular lesion of undetermined significance,” (FLUS) is also called “atypia of undetermined significance” (AUS). These are designations under the Bethesda system for thyroid cytopathology reporting. The AUS/FLUS findings represent Bethesda category III thyroid findings, which fall between category II (benign) and category IV (follicular neoplasm).

Based on the Bethesda nomenclature, you should not classify AUS/FLUS using other ICD-10 options such as the following:

• E04.- — Other nontoxic goiter (such as a single nodule like this case, E04.1, Nontoxic single thyroid nodule)
• D34 — Benign neoplasm of thyroid gland
• C73 — Malignant neoplasm of thyroid gland

Much debate surrounds the significance of AUS/FLUS findings from thyroid nodule fine needle aspiration (FNA). Various studies indicate different malignancy risk assessment for cases with that finding. Protocols also vary regarding whether to follow these FNA cases with a repeat FNA or some other additional testing, such as a molecular study or a thyroid biopsy.