Report interpretation

Repeat FNAC: — When and Why It Is Done Again

If your FNAC report has come back indeterminate, you are probably wondering whether that means cancer or whether you need surgery now. In most cases the answer to both is no — indeterminate means the sample did not give the laboratory enough to decide either way. A repeat test, after the right interval, often gives a clearer result.

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

Not a diagnosis — Indeterminate means the sample could not confirm benign or malignant — not that cancer has been found.
Repeat before surgery — Most guidelines recommend a repeat FNAC after a defined interval, not surgery as the first response to an indeterminate result.
Often resolves — In a proportion of patients, the repeat gives a definitively benign result and no further intervention is needed.
Your category matters — The Bethesda category on your report affects how long to wait and what comes next if the repeat is also indeterminate.

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A repeat FNAC is recommended when your first result was indeterminate — meaning the cytologist could not confirm benign or malignant from the sample. Most guidelines suggest waiting several months before repeating, to allow reactive changes to settle. In a proportion of patients, the repeat gives a clearer result and no further intervention is needed.

When does your doctor recommend repeating the FNAC?

An indeterminate result does not mean cancer has been found. It means the sample did not give the pathologist enough information to call the cells definitively benign or malignant. A repeat is ordered to try to get a more informative sample.

The most common reason for an indeterminate result is a sample problem — not enough cells, or cells obscured during preparation — rather than an ambiguous tumour. In those cases, a repeat often gives a clearer answer. If the cells themselves are genuinely equivocal, the repeat may still be indeterminate, and your team will discuss next steps from there.

Your doctor will tell you how long to wait before the repeat. Repeating too soon, before any inflammatory or reactive cells settle, can produce the same equivocal picture. Waiting the recommended interval is not a delay in your care — it is the approach recommended by ATA, NCCN and other major cytology guidelines.

What happens if the repeat result is still indeterminate?

	After first FNAC indeterminate	After repeat also indeterminate
Usual recommendation	Wait, then repeat FNAC	Discuss molecular testing or diagnostic surgery
What it does not mean	That cancer is present or that surgery is needed now	That cancer is definitely present — diagnosis still requires further assessment
Urgency	Planned, not urgent — typically weeks to schedule the repeat	Discuss next steps with your specialist team within a few weeks of the result
Outcome in a proportion of patients	Repeat gives a clearer benign or suspicious result	Molecular testing may resolve uncertainty without surgery
What drives the next decision	Bethesda category and nodule characteristics on ultrasound	Availability of molecular testing and the balance between surgical risk and diagnostic benefit

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What do the terms on your FNAC report mean?

Bethesda System: A six-category reporting system used for thyroid FNAC results in India and internationally. Each category carries a different level of concern and a different management recommendation. Your report will state a Bethesda category number and a written description alongside it.
Indeterminate: A result that falls into Bethesda categories III or IV. It means the cytology cannot be confidently called benign or malignant from this sample. It is not a diagnosis — it is a prompt for further assessment, usually beginning with a repeat FNAC.
AUS / FLUS — Bethesda III: Atypia of undetermined significance or follicular lesion of undetermined significance. The cells show some unusual features but not clearly malignant ones. A repeat FNAC is the step most commonly recommended next, and a proportion of these nodules are reclassified as benign on the repeat.
Follicular neoplasm — Bethesda IV: A category indicating a growth pattern that could be benign (follicular adenoma) or malignant (follicular carcinoma). A repeat FNAC is less likely to resolve this category; molecular testing or a diagnostic surgical removal is more often discussed from the outset.
Non-diagnostic — Bethesda I: The sample did not contain enough cells for assessment. This differs from an indeterminate result — it means the test was technically insufficient, not that the cells were ambiguous. A repeat is routine and usually gives an adequate sample.
Molecular testing: A laboratory analysis of FNAC material looking for specific gene changes associated with thyroid cancer. When available, it can resolve an indeterminate cytology result without surgery by shifting the probability toward benign or malignant.

Did you know?

In a proportion of thyroid nodules initially classified as indeterminate, a repeat FNAC reclassifies the result as clearly benign — which means no surgery and no further intervention is needed.

This is the central reason that guidelines recommend repeating rather than going straight to surgery. Whether your nodule falls in that group depends on the Bethesda category and on whether the first result reflected a sampling limitation or a genuinely ambiguous cell picture.

Source: American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer, 2015

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Common questions

Frequently asked questions

How long do I have to wait before the repeat FNAC?

ATA and NCCN guidance recommends an interval of several months before repeating, not weeks. The reason is that inflammatory cells at the biopsy site can make the picture look more ambiguous than the underlying nodule actually is — repeating too soon risks the same indeterminate result for a technical reason. Your doctor will give you a specific timeline based on your Bethesda category and clinical picture. The interval is deliberate, not neglect.

Does an indeterminate FNAC result probably mean cancer?

Not necessarily — and this is exactly why the result is called indeterminate rather than suspicious. Many nodules in this category turn out to be benign on repeat testing or after surgery. The Bethesda system acknowledges that some indeterminate results carry a risk, but a large proportion do not. Your oncologist or endocrinologist will explain what the balance looks like for your specific category and nodule features. This result calls for further assessment, not a conclusion.

What if the second FNAC is also indeterminate?

A second indeterminate result narrows the options. Most guidelines recommend discussing molecular testing on the FNAC material — this looks for gene changes that shift the probability toward benign or malignant. If molecular testing is unavailable or uninformative, diagnostic surgical removal is usually recommended. In many cases where surgery is performed for an indeterminate result, the final pathology shows the nodule is benign, though surgery also provides a definitive answer.

Is the repeat FNAC more painful or different from the first?

The procedure is identical. A fine needle passes into the nodule under ultrasound guidance and cells are drawn out. You may notice discomfort at the puncture site afterwards, the same as the first time. If you found the first procedure difficult, tell your team before the repeat — they can adjust positioning or add local anaesthetic. The repeat does not carry greater risk than the first.

Can I have the repeat FNAC done at a different centre?

Yes. Bring your original FNAC report and most recent ultrasound images to whichever centre you attend. A second cytopathologist reading without the first report in front of them is sometimes useful. Having the ultrasound done at the same centre helps compare nodule size accurately between tests, though this is not essential. Tell the new team that a repeat is being done specifically because the first result was indeterminate.

What if my nodule appears to have grown between the two tests?

Growth on ultrasound between the two tests can change the picture significantly. Your team may shorten the waiting interval or move directly to molecular testing or surgery rather than repeating. A nodule that is clearly enlarging shifts the risk assessment even if the cytology is unchanged. If you feel the lump is larger, contact your team rather than waiting for your scheduled review.

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