What Happens During a Thyroid Nodule Biopsy, and What Do the Results Mean?

The short answer: A thyroid nodule biopsy is a fine-needle aspiration (FNA). A doctor uses ultrasound to guide a thin needle into the nodule and draws out cells, usually in 2 to 6 quick passes. The visit usually takes less than 30 minutes, and most people go back to normal activities the same day. Results come back in a few days to 2 weeks, sorted into one of six Bethesda categories, from benign to malignant.

This article covers the biopsy itself and how to read the report. For how nodules are found and how ultrasound scores (TI-RADS) decide who needs a biopsy, see our thyroid nodules guide.

How do you prepare for a thyroid biopsy?

Preparation is minimal. The American Thyroid Association (ATA) patient page on FNA says most medicines can be continued, and you usually do not need to fast.

The main exception is blood thinners. The ATA says anticoagulants often need to be stopped for a short time because they raise the risk of bleeding. RadiologyInfo, the patient site of the American College of Radiology and the Radiological Society of North America, names aspirin, Lovenox, Plavix, and Coumadin as examples to tell your doctor about. Do not stop a blood thinner on your own. The office that does the biopsy, together with the doctor who prescribed the drug, should give you a written plan.

A few practical points from the ATA:

• Wear comfortable clothing and take off necklaces. The ultrasound gel can get on your collar.
• You generally do not need a driver. No sedating medicine is used for most adults.
• Bring a list of your medicines and any prior thyroid ultrasound reports.

What happens during the biopsy, step by step?

Thyroid FNA is usually done in an office or outpatient clinic, by an endocrinologist, radiologist, or surgeon. Here is the usual sequence, based on the ATA and RadiologyInfo descriptions:

1. Positioning. You lie on your back with a pillow under your shoulders and your head tipped back, so your neck is extended.
2. Cleaning and numbing. The skin is cleaned with antiseptic. A local or topical anesthetic may be used, but it is not always needed.
3. Ultrasound guidance. A probe with gel is placed on your neck so the doctor can watch the needle reach the nodule in real time.
4. Sampling. The doctor inserts a very thin needle, smaller than most blood-draw needles. RadiologyInfo says it is usually 25 or 27 gauge. Each pass takes only a few seconds. A new needle is used for each pass, usually 2 to 6 times, to sample different parts of the nodule. If the nodule holds fluid, a syringe may drain it.
5. Pressure. The doctor presses on the site to limit bleeding. A small bandage may go on. No stitches are needed.

During the passes, you will be asked not to talk, cough, or swallow. Most people feel pressure from the probe and brief discomfort as the needle moves. The whole visit usually lasts less than 30 minutes.

What is recovery like, and what are the risks?

Recovery is quick. The ATA says there are very few restrictions afterward. RadiologyInfo says the site may be sore and tender for one to two days. Acetaminophen and an ice pack usually help.

Complications are rare because the needle is fine and guided by imaging. RadiologyInfo lists bleeding at the site, infection, and injury to nearby structures as the possible risks. Call your doctor if your neck swells quickly, you have trouble breathing or swallowing, or you develop a fever.

Waiting for results can be the hardest part. If the wait is causing real worry, anxiety.md has practical guidance on coping with health anxiety.

How are thyroid biopsy results reported?

A cytopathologist looks at the cells under a microscope. The ATA says results take anywhere from a few days to 2 weeks. The report uses the Bethesda System for Reporting Thyroid Cytopathology. Its third edition, published in 2023, gave each of the six categories a single name and an updated average risk of cancer.

The figures below are the 2023 average risk of malignancy and range, as summarized in a peer-reviewed review of the third edition:

• I. Nondiagnostic: about 13% (5 to 20%). Not enough cells were collected to make a call.
• II. Benign: about 4% (2 to 7%). This is the most common result.
• III. Atypia of undetermined significance (AUS): about 22%.
• IV. Follicular neoplasm: about 30% (23 to 34%).
• V. Suspicious for malignancy: about 74% (67 to 83%).
• VI. Malignant: about 97% (97 to 100%). Papillary thyroid cancer is the most common type.

Two cautions. First, these are averages across many centers. The ATA notes that rates differ from one institution to another. Second, some older patient pages, including the ATA's own, still show earlier-edition numbers. For example, it lists a 5 to 15% risk for AUS. Your doctor may use the risk seen at your own center.

What does an indeterminate result mean?

"Indeterminate" usually means Bethesda III (AUS) or IV (follicular neoplasm). Enough cells were collected, but the cells alone cannot show whether the nodule is benign or cancer. A follicular neoplasm in particular can only be confirmed by looking at the whole nodule's edge after surgery.

Molecular testing is the main tool for these results. The test runs on extra cells from the same biopsy, so you do not need another needle in most cases. The ATA thyroid nodules page says these tests are most useful when the cytology is indeterminate.

A 2021 randomized trial in JAMA Oncology compared two widely used tests, Afirma GSC (an RNA test) and ThyroSeq v3 (a DNA and RNA test), in 346 patients with Bethesda III or IV nodules. Both tests had high specificity, with no significant difference between them. About 49% of patients avoided diagnostic surgery. Of the nodules that were later watched with ultrasound, 94% stayed stable over a median of 12 months.

What happens next for each result?

Next steps follow the Bethesda category, the ultrasound pattern, and your own preferences. The 2015 ATA thyroid nodule guidelines and the Bethesda management table outline the usual paths:

• Nondiagnostic: repeat the FNA with ultrasound guidance. If it is nondiagnostic again, the ATA says the options are a third biopsy, monitoring, or surgery.
• Benign: no surgery unless the nodule causes symptoms. The ATA advises a follow-up ultrasound, often within 18 months. A new biopsy may be needed if the nodule grows.
• AUS: repeat FNA, molecular testing, diagnostic lobectomy, or surveillance.
• Follicular neoplasm: molecular testing or diagnostic lobectomy (removing the half of the thyroid with the nodule).
• Suspicious for malignancy: molecular testing, lobectomy, or near-total thyroidectomy.
• Malignant: lobectomy or near-total thyroidectomy, planned with an experienced thyroid surgeon.

If surgery is the plan, our guide to thyroidectomy recovery time explains what the weeks after look like. A benign biopsy does not mean you stop follow-up. The ATA says surgery can still be advised if a benign nodule keeps growing or develops worrisome ultrasound features.

The bottom line

A thyroid FNA is a short office procedure with a thin needle, 2 to 6 passes, and a day or two of mild soreness. The main thing to plan ahead is any blood thinner, and that plan should come from your doctors. Most results are benign. Indeterminate results are common enough that molecular testing exists to sort them, and about half of tested patients in one trial avoided surgery. Ask which Bethesda category you received and what the next step is for that category at your center.

Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your endocrinologist or thyroid surgeon about your biopsy results and the right next step for you.