Most skin abscesses are easy to see, especially once they rupture and start to drain, but they may be difficult to detect in long-haired, heavily-coated breeds. Superficial abscesses are usually walled-off inside a protective fibrous capsule and feel firm, but somewhat squishy to the touch; at least before they rupture. Internal abscesses, such as those in the pancreas, lungs, liver or other organs, cannot be identified without more advanced techniques.
A veterinarian presented with a dog with a visible skin abscess or draining tract usually will take a blood sample for evaluation. Because abscesses almost always involve a bacterial infection, routine blood work on affected dogs usually will identify infection. If the prostate gland has abscessed, a urinalysis will show the presence of pus and blood in the urine, which is never normal. If the liver or pancreas have abscessed, blood levels of liver enzymes or total bilirubin may be elevated, and circulating amylase/lipase levels may also be abnormal. A veterinarian can discuss the meaning of these various blood sample results with owners in greater detail.
Radiographs (X-rays) and ultrasonography can both be used to look for inhaled or ingested foreign objects and to assess whether any internal masses are fluid-filled abscesses or solid tissue tumors. Computed tomography (CT scan) and magnetic resonance imaging (MRI) are available at veterinary teaching hospitals and some specialty referral centers and can be particularly helpful to identify abscesses in the brain. Echocardiography, which basically is an ultrasound scan of the heart, can be used to diagnose cardiac abscesses.
One of the most common techniques for evaluating the cause of an abscess is to take several samples of the pus from its center and examine those samples under a microscope. The pus from an abscess usually is pale, pinkish or red. Sometimes, it will have a greenish tinge. The veterinarian may need to lance an external abscess in order to get a good sample of its contents, and also to help it drain and heal. Internal abscesses can be sampled by taking surgical biopsies. This involves sedating the dog and removing either a part of the abscess through an incisional biopsy or removing the entire encapsulated abscess throughan excisional biopsy. Most veterinarians recommend taking biopsies of both healthy and unhealthy tissue from the affected area. Many times, the veterinarian will use an ultrasound for guidance when taking biopsies of abscesses from internal organs. The sampled tissue will be sent to a laboratory for detailed examination by a veterinary pathologist. There are a number of different techniques that can be used to identify the precise active microorganisms that caused an abscess to form. Usually, some combination of bacteria is involved. It is important to figure out what type of bacteria caused the infection, so that a full course of appropriate antibiotics can be prescribed for the affected animal.