Inconclusive or Non-Diagnostic Thyroid FNA: What Happens Next?

A non-diagnostic thyroid FNA means the needle sample did not contain enough well-preserved thyroid cells for a reliable answer. It is reported as Bethesda category I (nondiagnostic or unsatisfactory) and is neither a benign nor a cancer result. The usual next step is a repeat ultrasound-guided biopsy.

People often hear this called an inconclusive or inadequate result. Be aware that "inconclusive" is sometimes used loosely for indeterminate results (Bethesda 3 or 4), which are different. Check the exact category on the report. This guide explains the questions to ask; it cannot interpret your own sample.

A non-diagnostic result can be frustrating, especially after waiting for an answer. It simply means the question the biopsy was meant to answer is still open, so a plan for getting that answer is needed.

Difficulty breathing, or being more short of breath than usual, needs prompt help. The NHS advises an urgent GP appointment or NHS 111 for this; if breathing is severely difficult, call local emergency services. Do not wait for a planned scan.

Contact your clinician before the repeat biopsy if you notice any of the following. The neck symptoms are listed by the NHS as reasons to see a GP.

• A neck lump that is clearly getting bigger, or a new lump.
• A hoarse voice that is not getting better.
• Difficulty swallowing that is not getting better.
• Pain in the front of the neck, or a feeling that something is pressing on it.
• After the biopsy: fever, chills, or redness, swelling or pus at the needle site, which Cleveland Clinic lists as possible signs of infection.

The Bethesda System sorts thyroid FNA results into six categories. Category I covers samples that do not meet set standards for adequacy. The 2015 ATA guideline describes the usual standard as at least six groups of well-visualised follicular (thyroid) cells, each with at least 10 well-preserved cells. Laboratories apply these criteria, not patients.

Non-diagnostic results are not rare. The guideline reports they made up 2–16% of FNA samples in large series. The ATA patient page says the figure is under 5% when ultrasound is used to guide the needle.

A non-diagnostic result does not by itself mean the procedure was done wrongly. RadiologyInfo notes that specimens are sometimes inadequate and the procedure may need repeating. Situations described in the ATA sources include:

• The nodule is mostly fluid, so the needle draws up few thyroid cells.
• The sample has too few well-preserved cells to meet the laboratory's adequacy standard.
• The sample shows plenty of colloid (a protein-rich thyroid substance) but few cells. The 2015 ATA guideline notes this can meet non-diagnostic criteria yet is likely to be a benign biopsy, so ask how your report describes it.

The ATA patient page says a non-diagnostic result is common if the nodule is a cyst, because not enough cells are obtained. The 2015 ATA guideline adds that nodules with a larger cystic portion are more likely to give non-diagnostic samples on both the first and repeated FNA.

If your scan showed a cystic or mixed nodule, the thyroid cyst guide explains those patterns. Ask whether the solid part of the nodule was the target of the biopsy, and whether that changes the plan. A fluid-filled nodule that gives a non-diagnostic result is a common situation, but the decision about what to do next still rests with your team, who can weigh the ultrasound appearance alongside the sample.

The 2015 ATA guideline recommends repeating the FNA with ultrasound guidance and, where available, on-site checking of the sample so adequacy can be judged during the procedure. In large series, a repeat ultrasound-guided FNA gave a diagnostic sample in 60–80% of nodules, with a lower yield in more cystic nodules.

On timing, the guideline notes it had been suggested to wait at least 3 months after the first FNA, but states that a 3-month waiting period after a non-diagnostic biopsy is likely not necessary. Your team will set the actual timing.

The repeat procedure is usually similar to the first. RadiologyInfo explains that new needles are used if more samples are needed, and that the biopsy site may be sore and tender for one to two days. The NHS notes that biopsy results usually take around two weeks, and a delay does not necessarily mean something is wrong.

For nodules that are repeatedly non-diagnostic, the 2015 ATA guideline describes close observation or surgical removal for nodules without a high-suspicion ultrasound pattern. Surgery should be considered for a diagnosis if the nodule has a high-suspicion pattern, if it grows by more than 20% in two dimensions during ultrasound follow-up, or if there are clinical risk factors.

The guideline also mentions core needle biopsy, which can give an adequate sample more often but may be less sensitive for one type of thyroid cancer. Which option fits depends on your nodule and history. Ask your team to explain the trade-offs of each option for your situation, and how long you would wait for each.

Bring the biopsy report and the ultrasound report to the appointment.

• Was my result Bethesda I (non-diagnostic), or an indeterminate category?
• Why do you think the sample was insufficient? Was the nodule mostly fluid?
• What ultrasound pattern or TI-RADS score did the nodule have?
• When will the repeat FNA be, and will it use ultrasound guidance and on-site sample checking?
• If the repeat is also non-diagnostic, would you suggest observation, core biopsy or surgery, and why?
• Which symptoms should make me contact you before the repeat biopsy?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a non-diagnostic thyroid FNA went through repeat biopsy or follow-up can help you prepare questions, such as how the cystic part of a nodule was handled. Other people's cases cannot tell you what your result means or what will happen next for you, and we make no promises about outcomes.