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When it comes to swollen lymph nodes in dogs, proper diagnostic testing is important considering the risks for serious conditions such as lymphoma. 

There are several different tests used to check for the underlying cause for swollen lymph nodes in dogs, but which ones are the best? 

So far, there seem to be two main ways those swollen lymph nodes can be tested to rule out or confirm the presence of cancer: a fine needle aspiration or a biopsy.

 Let's see what experts say on both of these types of tests along with their pros and cons for each of them.

dog raised hackles

Fine Needle Aspirate

A fine needle aspirate (FNA) is simply a needle that aspirates (sucks out) the contents of the swollen lymph node. 

The contents, which are most cells, are then placed on a glass slide and then sent out to a veterinary pathologist to evaluate.

This is the quickest, less costly and least invasive procedure ( in most cases, no sedation is needed) and often the first most vets rely on when a dog presents with swollen lymph nodes.

Afterward, the cells are looked at and one can determine if the lymph nodes are just reactive or affected by cancer.

Reactive lymph nodes are simply swollen because of underlying infection or inflammation.

 Cancer of the lymph nodes (lymphoma), on the other hand, is known for causing multiple lymph nodes to enlarge. 

When the results of a fine needle aspirate are inconclusive (an exact cause for the swollen lymph nodes is not found) the vet may recommend an incisional biopsy.

Did you know? In lymph glands due to inflammation or infection, samples show reactive lymphoid inflammatory cells, with a predominant population of small lymphocytes (the dog's immune system's disease-fighting cells) along with other possible inflammatory cells like neutrophils and eosinophils. 

Normal lymph nodes have hardly inflammatory cells in the, explains veterinarian Dr. Matt. In lymphoma instead, there are mostly large neoplastic lymphoid cells, with less variety.

Incisional/Excisional Biopsy

Raised hackles during rough play

An incisional or excisional biopsy is often performed after fine-needle aspiration and its cytology report suggests the presence of disease.

 An incisional/excisional biopsy is performed with the dog under total anesthesia since an incision must be made to the lymph node and a piece, wedge, or the entire lymph node is removed.

There is a difference between an an incisional biopsy and an excisional biopsy.

 In an incisional biopsy, only a part of a lymph node will be removed, while in an excisional biopsy, the entire lymph node will be taken out.

Generally, the larger the sample, the more accurate the diagnosis.

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 Entire lymph node removal should be performed when possible as this gives the pathologist the ability to observe the architecture of the entire lymph node and determine whether capsular invasion exists.

 This is particularly helpful for differentiating lymphoma from lymph node hyperplasia (enlargement).

Once the lymph node is removed it is "bread sliced" so to allow adequate exposure to formalin and then sent to a veterinary pathologist to examine. 

The pathologist will therefore examine it, dissect it and look at it under a microscope to determine with more accuracy the underlying cause for the swollen glands.

If the sample is suggestive of cancer, the pathologist may also be able to determine the presence of T cells or B cells and therefore it is possible to assess the grade and stage and the cancer. 

Biopsy is therefore often recommended, after a diagnosis for lymphoma is made through a fine needle aspirate, as it allows to get a clearer picture about whether it's a B cell or T cell lymphoma, the over all grade and stage or the cancer and prognosis, explains veterinarian Dr. B, board, certified veterinarian.

Did you know? While a dog's fine needle aspirate may generally cost around $200 a dog biopsy may cost closer to $500 to $800 since it requires sedation/anesthesia.

Needle Core Biopsy Option

There is actually a third type of test that can done in the case of a dog swollen lymph node. This is just another type of biopsy in dogs. 

The main advantage of needle core biopsy is the fact that it can be done on an awake dog as long as cooperative and not fractious.

The main advantage is that the results are more accurate compared to a fine-needle aspiration, but yet, not as accurate as the results attained through an excisional biopsy.

Is the procedure painful? When a needle core biopsy is done, the skin is injected with lidocaine. This anesthetizes the skin, so that the dog doesn't feel pain. Afterward, samples are taken using a needle core biopsy instrument and are then preserved in formalin and sent out to a pathologist.

The cost of needle core biopsy in dogs is generally middle range between the price of a fine needle aspirate and an excisional biopsy. You may expect to pay around $300 to $600.

Other Tests

Prior to lymph node biopsy, the vet will likely want to perform some routine screening tests so to identify metabolic disease or coagulopathies (problems with the blood's ability to clot).

If dogs have other problems along with the swollen lymph nodes, further tests are often recommended.

Chest and/or abdominal x-rays and an ultrasound to check the dog's liver and internal lymph nodes can help assess a dog's overall state of health and rule our spread of certain cancers.

Blood tests (a full blood panel) may also be helpful as a high white blood cells may indicate presence of an infection, and urinalysis, bone marrow aspirate can also be suggested by a vet for diagnosis.

If the swollen lymph nodes is located in only one area, a careful examination of the area can reveal presence of inflammation or infection. Usually, if the dog is asymptomatic though, further testing is done once the results from the fine needle needle aspiration or biopsy come in.


  • Canine lymphosarcoma: Overcoming diagnostic obstacles and introduction to the latest diagnostic techniques, Ryan M. Dickinson, Can Vet J. 2008 Mar; 49(3): 305–308
  • Today's Veterinary Practice, Lymph Node Cytology, What Should & Should Not Be There retrieved from the web on October 15th, 2016
  • Managing the Veterinary Cancer Patient, Gregory K. Ogilvie, Antony S. Moore, Veterinary Learning Systems

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