What Is Next After a Bethesda I Nondiagnostic Thyroid FNA?

When a thyroid biopsy (Fine Needle Aspiration, or FNA) comes back as “Bethesda I” or “nondiagnostic,” it means the sample did not contain enough usable cells to make a diagnosis ^{[1] [2]}. It is very important to understand that a Bethesda I result is neither a benign (non-cancerous) diagnosis nor a cancer diagnosis ^[2]. It simply means the laboratory does not have the information needed to tell you what the nodule is. Your actual risk of cancer is not based on this Bethesda I result, but rather on the nodule’s appearance on ultrasound, its size, your symptoms, and other clinical factors ^[3].

Because the nodule remains undiagnosed, the standard next step is usually to repeat the biopsy, though some situations may call for other testing, active monitoring, or even surgery ^[2].

Why Was My Biopsy Nondiagnostic?

A Bethesda I result happens when the specialist evaluating the slide (a cytopathologist) cannot see enough clearly defined thyroid cells. Common reasons for this include:

• Heavily cystic nodules: If your nodule is mostly filled with fluid (a cyst) rather than solid tissue, the needle may only draw out fluid and not capture enough actual cells ^{[4] [5]}.
• Too much blood: Sometimes the needle hits a tiny blood vessel, and the resulting sample is mostly blood, which obscures the thyroid cells ^{[6] [7]}. (Note: Having a bloody sample does not necessarily mean you are on blood thinners, and you should never stop medication without your doctor’s advice ^[8]).
• Scant cells: The needle simply didn’t pick up enough follicular cells (the main cells of the thyroid) to meet the criteria for a proper diagnosis ^[1].
• Technical limitations: The size or depth of the nodule can affect the sample ^{[4] [9]}. Additionally, having rapid on-site adequacy assessment (where qualified personnel check the sample during the procedure to ensure enough cells were gathered) can help reduce nondiagnostic results, but it is not available at every clinic ^[10].

The Role of TSH and Thyroid Scans

Checking the level of Thyroid Stimulating Hormone (TSH) in your blood is a routine part of evaluating any thyroid nodule, including those in a multinodular goiter.

If your TSH is low, it indicates your thyroid is overactive. When this happens, a radionuclide diagnostic scan (scintigraphy) is typically the recommended next step before repeating a biopsy ^[11]. This scan uses a small amount of a radioactive tracer to show which nodules are producing too much hormone (“hot” nodules) and which are inactive (“cold” nodules) ^{[12] [13]}. (Note: A diagnostic scan is a low-dose imaging test, different from radioactive iodine treatment. However, you must inform your doctor if you are pregnant, trying to become pregnant, or breastfeeding, as the tracer may not be appropriate).

• “Hot” Nodules: Clearly hyperfunctioning (hot) nodules have a low risk of cancer ^[14]. While the risk is not zero, these nodules are generally excluded from routine biopsy guidelines ^[12].
• “Cold” Nodules: Nonfunctioning (cold) nodules do not produce excess hormone. They are evaluated based on their ultrasound risk features and may still require a repeat biopsy ^{[11] [15]}.

The Standard Next Step: Repeat Biopsy

For most patients with normal or high TSH, the immediate priority is to try again with a repeat ultrasound-guided FNA ^[2]. During the second attempt, the doctor will use the ultrasound to specifically target the solid parts of the nodule rather than the fluid-filled areas ^{[3] [2]}.

Research shows that a repeat FNA yields a diagnostic sample in about 65% to 79% of cases ^{[16] [17]}. Getting a diagnostic sample means the lab has enough cells to evaluate; the final result could still be benign, indeterminate, or malignant.

When should the repeat biopsy happen? In the past, doctors often waited about three months before repeating the biopsy. However, studies show there is no significant difference in diagnostic success whether the biopsy is repeated before or after three months ^[18]. If your nodule has suspicious features on an ultrasound, your doctor may recommend repeating the biopsy sooner ^[16]. For nodules with a very low risk of cancer based on ultrasound, observation (close monitoring with periodic ultrasounds) may be a reasonable alternative to a repeat biopsy ^[3].

What If the Nodule is Still Nondiagnostic?

If a repeat sample is also Bethesda I, your doctor will discuss alternative options with you:

• Core Needle Biopsy (CNB): A core biopsy uses a slightly larger, hollow needle to remove a tiny, solid cylinder of tissue. Selected meta-analyses have shown that CNB can have a lower nondiagnostic rate (around 6.4%) compared to repeat FNA (around 36.5%) and improved sensitivity ^[19]. However, CNB is an option for certain cases rather than a universal replacement for FNA; it carries rare risks like bleeding and pain, and it may not definitively resolve some indeterminate diagnoses (like telling a benign follicular adenoma apart from a carcinoma).
• Diagnostic Surgery: If a nodule repeatedly fails to provide a good sample, is growing rapidly, or has highly suspicious ultrasound features—such as microcalcifications (tiny calcium spots), irregular margins (uneven edges), or a taller-than-wide shape—your care team may suggest diagnostic surgery to remove that part of the thyroid ^{[3] [20]}.

Diagnostic surgery (such as removing one half of the thyroid, called a lobectomy) is a shared decision based on your clinical risk factors and preferences. It is not automatic. Your doctor will discuss the tradeoffs of surgery, which can include a small risk of bleeding, voice-nerve injury, low calcium levels, and the possibility of needing thyroid hormone replacement medication or further treatment afterward.

When to Seek Immediate Care

• Seek urgent emergency care if you experience trouble breathing, rapidly increasing neck swelling, an inability to swallow saliva, or significant bleeding after a biopsy procedure.
• Contact your care team promptly if you notice a new or worsening change in your voice, worsening pain, fever, or progressive difficulty swallowing (compressive symptoms from the goiter).