Thyroid Biopsy Test: Purpose, Test Details & Results

Thyroid nodules are a common clinical finding, raising concern for possible thyroid cancer or other thyroid disorders. While most thyroid nodules are benign, distinguishing between malignant and benign nodules is crucial to guide appropriate treatment and avoid unnecessary surgery. The thyroid biopsy—most commonly performed as a fine-needle aspiration (FNA) or core-needle biopsy (CNB)—has become the cornerstone for evaluating thyroid nodules. In this comprehensive article, we’ll explore why thyroid biopsies are performed, how the tests are conducted, and how to interpret the results and next steps.

Purpose of Thyroid Biopsy Test

When a thyroid nodule is detected, either by physical examination or imaging, the main question is whether it is cancerous or benign. Thyroid biopsy tests are designed to answer this question in the most accurate and least invasive way possible.

Indication	Goal	Impact	Source(s)
Thyroid nodule	Assess malignancy risk	Guides treatment, avoids unnecessary surgery	1, 3, 4
Suspicious imaging or growth	Confirm diagnosis	Improves cancer detection rates	1, 7
Inconclusive prior results	Achieve conclusive diagnosis	Reduces repeat surgeries and procedures	5, 9
High-risk patient (e.g., prior radiation)	Early detection	Enables timely intervention	1

Table 1: Purposes and Impacts of Thyroid Biopsy Tests

Why Biopsy?

Thyroid nodules are found in up to 7% of adults and are even more common in women, older adults, and people with a history of radiation exposure or iodine deficiency. While most nodules are benign, about 3-5% are malignant, making accurate diagnosis vital 1. Clinical assessment, ultrasound, and other imaging can raise suspicion, but only biopsy provides direct cellular evidence of malignancy or benignity 1 3.

Reducing Unnecessary Surgery

Before the widespread use of biopsy, many patients with nodules underwent surgery simply to rule out cancer—resulting in numerous unnecessary operations. The introduction of FNA has led to a 25% reduction in thyroid surgeries and a higher rate of cancer detection in those who do undergo surgery (from 14% up to 30%) 3. This means more selective and appropriate use of surgery, benefiting patients both medically and economically.

When Is a Biopsy Needed?

A thyroid biopsy is generally recommended when:

• A thyroid nodule is detected that is solid, >1cm, or has suspicious features on ultrasound
• There is rapid nodule growth, fixity, or associated lymphadenopathy
• Previous FNA or imaging was inconclusive or suspicious
• There are risk factors for malignancy (e.g., childhood head/neck irradiation, family history) 1 8

Special Cases

Biopsies are also important when a patient has a history of cancer elsewhere, as the thyroid can be a rare site for metastasis. In such cases, CNB is often preferred for its ability to provide more tissue for additional testing, such as immunohistochemistry 5.

Thyroid Biopsy Test Details

Understanding how a thyroid biopsy is performed helps demystify the process and reduces patient anxiety. The two main techniques—fine-needle aspiration (FNA) and core-needle biopsy (CNB)—each have distinct roles and advantages.

Method	Procedure Highlights	Diagnostic Accuracy	Source(s)
FNA	Thin needle, outpatient, minimal discomfort	~90%+ (expert centers)	1, 3, 4, 7
CNB	Thicker needle, US-guided, provides tissue core	Sensitivity 94-96%, Specificity 88-94%	2, 9, 11
US guidance	Accurate targeting, less risk	Enables biopsy of small/deep nodules	6
Complications	Rare, mostly minor (hematoma, pain)	No major risks reported	1, 2, 11

Table 2: Thyroid Biopsy Methods and Key Features

Fine-Needle Aspiration (FNA)

How it works:

• Performed in a clinic with patient lying on their back, neck extended
• The skin is cleaned; usually, no anesthesia is needed
• A thin (23-25 gauge) needle is inserted into the nodule, sometimes with ultrasound guidance
• Material is aspirated and smeared onto slides for cytological analysis
• Multiple passes (usually 2-6) may be done to improve sample adequacy 1

Advantages:

• Minimally invasive and quick
• Rarely causes significant pain or complications
• Highly cost-effective
• Can be repeated if initial sample is non-diagnostic 1 3 6

Limitations:

• Sometimes yields insufficient cells (non-diagnostic)
• Can have indeterminate or suspicious results requiring further testing 1 8 9

Core-Needle Biopsy (CNB)

How it works:

• Performed with a thicker needle (16-18 gauge) under direct ultrasound guidance
• Obtains a core of tissue, preserving architecture
• Particularly useful after inconclusive FNA or for suspected metastasis 2 5 9

Advantages:

• Higher rate of conclusive results after non-diagnostic FNA
• Provides more tissue for ancillary studies (e.g., immunohistochemistry)
• Lower repeat biopsy and surgical rates in some studies 5 9 11

Limitations:

• Slightly higher risk of minor bleeding or discomfort
• More technically demanding, requires ultrasound guidance
• Not always needed as first-line test 2 7 9

Ultrasound Guidance

Ultrasound guidance greatly improves the accuracy of both FNA and CNB, allowing:

• Targeting of small (<1cm) or deep nodules
• Avoidance of blood vessels and critical structures
• Real-time visualization for safer, more effective sampling 6

Safety and Complications

Both FNA and CNB are considered very safe procedures. Minor side effects include:

• Temporary pain or mild swelling
• Small hematomas (bruises)
• Rarely, minor bleeding or hemoptysis (coughing blood) 1 2 11

Serious complications are extremely rare, and most patients can return to normal activities immediately after the procedure.

Thyroid Biopsy Test Results & Follow-Up

Once a thyroid biopsy is performed, the results guide next steps. Understanding what the results mean and what to expect is crucial for patients and clinicians alike.

Result Category	Meaning/Implication	Recommended Next Steps	Source(s)
Benign	No malignancy detected	Clinical follow-up	1, 3, 4, 11
Malignant	Cancer cells identified	Surgical consultation	1, 3, 4, 11
Suspicious/Indeterminate	Unclear, possibly neoplastic	Repeat biopsy or surgery	1, 8, 9, 11
Non-diagnostic	Insufficient material	Repeat biopsy (FNA or CNB)	1, 9, 11

Table 3: Thyroid Biopsy Result Categories and Actions

How Are Results Reported?

Biopsy results generally fall into four categories:

• Benign: Most common (53–90% of cases). No cancer detected; includes colloid nodules, thyroiditis, and other non-cancerous conditions 1 3.
• Malignant: Cancer cells are present (1–10% of cases). Most commonly papillary thyroid carcinoma, but can include other types. Requires surgical management 1 3 4.
• Suspicious/Indeterminate: Unclear risk; may be due to follicular or Hurthle cell neoplasms, or cellular atypia. Further evaluation, repeat biopsy, or surgery is often needed 1 8 9 11.
• Non-diagnostic (Unsatisfactory): Not enough cells to make a diagnosis (2–21% of cases). Repeat biopsy, often with ultrasound guidance or CNB, is recommended 1 9 11.

Sensitivity, Specificity, and Accuracy

• FNA: Sensitivity (ability to detect cancer when present) ranges from 58–90%+; specificity (correctly identifying benign nodules) is typically high (~81–99%) 1 3 4 7.
• CNB: Sensitivity and specificity are both high (94–96% and 88–94%, respectively), especially after a non-diagnostic FNA 2 9 11.
• False-negatives: Occur in up to 5–11% of cases, often due to sampling error or interpretive limitations. Larger nodules (>4cm) and certain ultrasound features may warrant closer follow-up even after a benign result 1 8.

What Happens After the Results?

Benign Results

• Most patients with benign cytology avoid surgery.
• Recommended follow-up includes periodic ultrasound and clinical examination.
• Repeat biopsy if the nodule grows, changes, or new symptoms develop 1 3 8.

Malignant Results

• Referral to a surgeon or multidisciplinary cancer team.
• Additional imaging and laboratory studies may be needed for staging.
• Surgery is typically indicated 1 3 4.

Suspicious/Indeterminate Results

• If features suggest possible cancer, surgery may be recommended.
• In some cases, repeat FNA or CNB is done for clarification.
• Some indeterminate lesions with low-risk features may be followed with observation and repeat biopsy 1 8 9 11.

Non-diagnostic Results

• Repeat FNA or CNB, ideally with ultrasound guidance, is advised.
• CNB has a higher conclusive rate for previously non-diagnostic nodules 9 11.
• Persistent non-diagnostic results with suspicious features may warrant surgery 9 11.

Special Considerations

• Metastasis to Thyroid: In rare cases, the thyroid may be a site of metastasis from other cancers. CNB is especially valuable here for its diagnostic yield 5.
• Repeated Biopsies: Sometimes needed, as up to 18% of thyroid cancers are diagnosed more than a year after the first biopsy 10.

Conclusion

Thyroid biopsy—most often via FNA, sometimes with CNB—is a safe, reliable, and cost-effective tool for evaluating thyroid nodules and guiding management. It reduces unnecessary surgery and enables more accurate, timely diagnosis of thyroid cancer.

Key Points:

• Purpose: Thyroid biopsy distinguishes benign from malignant nodules, guides treatment, and avoids unnecessary surgery 1 3.
• Test details: FNA is the mainstay; CNB is valuable for inconclusive or complex cases. Both are highly accurate and safe, especially with ultrasound guidance 1 2 3 9 11.
• Results: Most biopsies are benign; malignant, suspicious, or non-diagnostic results require further action. Repeat biopsy and follow-up are essential in indeterminate cases 1 3 8 9 11.
• Patient impact: Biopsy reduces overtreatment, increases cancer detection rates in those who need surgery, and provides peace of mind for the majority with benign nodules 3 10.

With continued advances in technique and interpretation, thyroid biopsy remains the gold standard for evaluating thyroid nodules and ensuring each patient receives the most appropriate care.