The Complete Guide to Interpreting Lymph Node Aspiration Results

ImmunityQ&AMeongsiljang Veterinary Advisory Board

Lymph node aspiration is the most basic and safe diagnostic method to find the cause of swollen lymph nodes. I'll explain the terms and their meanings on the result sheet in a way that's easy for pet owners to understand.

What is a Lymph Node Aspiration?

Illustration of the process for performing a lymph node aspiration test on a puppy

A lymph node aspiration is a diagnostic test in which a thin needle is inserted into an enlarged lymph node to withdraw cells for microscopic examination. It is the most basic diagnostic procedure, performed on an outpatient basis without anesthesia and typically completed within five minutes. The key advantage is rapid results: within one to three days, we can determine whether the swelling is due to simple inflammation or indicates a more serious issue such as infection or a tumor. Although the terminology on the report may seem complex, understanding the overall interpretation is straightforward.

Why Perform a Lymph Node Test?

Lymph nodes are immune gateways scattered throughout your pet’s body. You can feel them under the jaw, in front of the shoulders, in the armpits, in the groin, and behind the knees. If any of these areas have swollen from the size of a pea to that of a quail egg, or if they’re asymmetrically enlarged, testing is needed. While it could be a temporary immune response like a mild cold, it might also signal lymphoma or cancer spreading from elsewhere to the lymph nodes, so it’s important to identify the cause promptly.

Lymph Node Locations Pet Owners Can Palpate

Regularly and gently checking these five areas will help you quickly notice any changes. A normal lymph node feels like a small, smooth, movable pea.

Anatomical diagram of major lymph node locations in dogs

Major Lymph Node Locations and Normal Size

Item	How to find	Normal size criteria
Submandibular lymph nodes	Gently press both sides under the jaw	Bean size
Prescapular lymph nodes	Inner side at the base of the forelimb	Bean size
Axillary lymph nodes	Deep on the inner side of the forelimb	Normally hard to palpate
Inguinal lymph nodes	Inner side at the base of the hindlimb	Bean to quail egg size
Popliteal lymph nodes	Behind the knee joint of the hindlimb	Bean size

If it is larger than a quail egg or there is a clear left-right difference, get it examined.

Explanation of Key Terms on the Test Result Sheet

When you receive the test results, you might feel overwhelmed by unfamiliar medical terms. However, understanding just four key terms can help you grasp the overall picture. - Reactive hyperplasia: This indicates that immune cells are actively working. It is usually benign. - Lymphadenitis: This refers to inflammation or infection within the lymph nodes themselves. - Lymphoma: This means the lymph node cells have become cancerous. Further testing is required. - Metastasis: This occurs when cancer cells from another part of the body have spread to the lymph nodes.

Microscopic image of a lymph node cell examination

These Results Require Immediate Follow-up Testing

If your results include terms like “suspected lymphoma,” “malignant cells detected,” or “metastatic tumor cells,” schedule a follow-up test within 24 to 48 hours. Lymphoma can progress rapidly, so even a few days’ delay can significantly impact treatment timing. Additionally, because fine-needle aspiration alone often isn’t sufficient for a definitive diagnosis, your veterinarian may recommend a lymph node excisional biopsy, immunophenotyping, and thoracic and abdominal imaging. Don’t wait—confirm your appointment with your vet right away.

Is Aspiration Accurate? It Has Limitations

Lymph node aspiration is a quick and safe procedure, but it doesn’t always provide a definitive diagnosis. If only a small number of cells are collected or if the tumor is only partially present within the lymph node, it may be missed. Therefore, if the result is labeled as "non-diagnostic" or "further testing recommended," a full lymph node biopsy may be performed. Please remember that even if the initial result is positive, if the lymph node continues to grow, further testing may be necessary.

What to Monitor at Home After the Test

While the procedure itself is minimally invasive, please monitor your pet for the following signs at home over the next few days: - Swelling at the site: Contact the clinic if swelling at the examination site persists or worsens beyond 24 hours. - Bleeding or scabbing: Minor bleeding is normal, but if it does not stop, a veterinary examination is required. - General condition: Note any unusual lethargy or decreased appetite compared to your pet’s normal behavior. - Changes in lymph node size: Check for size changes by gently palpating the node at the same time each day. - Swelling in other lymph nodes: Monitor for new swelling in lymph nodes in other areas of the body.

A pet owner checking their dog's lymph nodes at home

Cat Owners Should Pay Extra Attention

Lymphoma is one of the most common hematopoietic cancers in cats. If your cat suddenly loses appetite, loses weight, and you notice enlarged lymph nodes, do not delay fine-needle aspiration. Feline lymphoma can develop in various locations, including the gastrointestinal tract (mesenteric lymph nodes) and the thymus or mediastinum, so imaging studies such as abdominal ultrasound and thoracic radiographs are often performed alongside lymph node examination. If multiple lymph nodes are enlarged, it is recommended to sample several nodes rather than just one. If fine-needle aspiration yields inconclusive results, an excisional biopsy may be necessary. Even if your cat appears to be in good condition, early diagnosis is crucial for determining the appropriate treatment plan.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Does a lymph node aspiration test require anesthesia?

Most procedures can be completed without anesthesia, with the owner simply holding the pet in place for a short time. However, since accessing deep lymph nodes (such as those in the chest or abdominal cavity) requires ultrasound guidance, mild sedation may be necessary.

How long does it take for the test results to come back?

If we examine the slides directly at our clinic, you’ll receive the initial findings the same day. If the samples are sent to an external laboratory, it typically takes about 2 to 5 days. If lymphoma is suspected, additional immunophenotyping will require an extra 1 to 2 weeks.

My pet’s lymph nodes are swollen, but they seem otherwise fine. Is it okay to just leave them alone?

No. In the early stages of lymphoma, there are often very few noticeable changes in your pet's overall condition. However, if you notice a swelling larger than a quail egg or one that is asymmetrical, it's important to have it checked by a veterinarian regardless of how your pet is feeling.

How much does the test cost?

Costs vary by clinic, so it’s best to contact your veterinarian directly for an exact estimate. Typically, aspiration and cytology are performed together, and additional fees may apply if samples are sent to an external laboratory for analysis.

Can lymphoma be definitively diagnosed with a single test?

While aspiration cytology can raise strong suspicion, a definitive diagnosis and treatment plan often require lymph node excisional biopsy combined with immunophenotyping.

Primary vs. Secondary Veterinary Hospitals: A Comparison

Comparing Dog Vaccine Types (3-way, 5-way, 7-way): Differences and How to Choose

Pet Insurance Enrollment Timing Comparison: When Is the Most Advantageous Time to Enroll?

A Complete Guide to the Causes, Behavioral Modifications, and Treatment of Canine Cognitive Dysfunction

If Your Cat Repeats the Same Behavior — Signs of Compulsive Disorder and Treatment

What is Canine Compulsive Disorder? — From Causes to Behavioral Modification and Treatment Timing

How to Use Medication for Canine Noise Phobia — From Types to Timing

Where Do Cat Tapeworms Come From? — The Flea Infection Cycle and Deworming Timing

What are hookworms in puppies? — Why do anemia and weight loss occur?

Can Dogs Eat Macadamia Nuts? — Toxicity Symptoms and Emergency Response

References

[1] Veterinary Surgical Oncology, 2nd Edition, Chapter 14 Hemolymphatic System, Deanna R. Worley, 2022

[2] The Cat, Clinical Medicine and Management, 2nd Edition, Cytology Chapter

[3] Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat, 5th Edition