In some cases, abscesses may be prevented by draining an existing pseudocyst which is likely to become inflamed. However, in most cases the developing of abscesses cannot be prevented.

Most patients who develop pancreatic abscesses have had pancreatitis, so a complete medical history is required as a first step in diagnosing abscesses. On the other hand, a white blood cell count is the only laboratory test that may indicate the presence of an abscess.

Some of the imaging tests are more commonly used to diagnose this condition. Abdominal CT scans, MRIs and ultrasounds are helpful in providing clear images of the inside of the abdomen and successfully used in the diagnosing process. These tests may reveal the presence of infected necrosis which has not yet developed into an abscess and as a result, doctors usually order repeated imaging tests in patients with acute pancreatitis whose abdominal pain worsens and who develop signs of abdominal obstruction. Also, it is recommended that patients who have a prolonged clinical response are tested repeatedly as a prevention method to avoid the development of an abscess that may rupture.

For those with a history of intravenous drug use, an X-ray is recommended before treatment to verify that no needle fragments are present. In this population if there is also a fever present infectious endocarditis should be considered.

Even without treatment they rarely result in death as they will naturally break through the skin.

There are three major forms of liver abscess, classified by cause:

- Pyogenic liver abscess, which is most often polymicrobial, accounts for 80% of hepatic abscess cases in the United States.

- Amoebic liver abscess due to "Entamoeba histolytica" accounts for 10% of cases.

- Fungal abscess, most often due to "Candida" species, accounts for less than 10% of cases.

Major bacterial causes of liver abscess include the following:

- "Streptococcus" species (including "Enterococcus")

- "Escherichia" species

- "Staphylococcus" species

- "Klebsiella" species (Higher rates in the Far East)

- Anaerobes (including "Bacteroides" species)

- "Pseudomonas" species

- "Proteus" species

However, as noted above, many cases are polymicrobial.

Diagnosis and the imaging (and laboratory) studies to be ordered largely depend on the patient history, signs and symptoms. If a persistent sore throat with signs of sepsis are found, physicians are cautioned to screen for Lemierre's syndrome.

Laboratory investigations reveal signs of a bacterial infection with elevated C-reactive protein, erythrocyte sedimentation rate and white blood cells (notably neutrophils). Platelet count can be low or high. Liver and kidney function tests are often abnormal.

Thrombosis of the internal jugular vein can be displayed with sonography. Thrombi that have developed recently have low echogenicity or echogenicity similar to the flowing blood, and in such cases pressure with the ultrasound probe show a non-compressible jugular vein - a sure sign of thrombosis. Also color or power Doppler ultrasound identify a low echogenicity blood clot. A CT scan or an MRI scan is more sensitive in displaying the thrombus of the intra-thoracic retrosternal veins, but are rarely needed.

Chest X-ray and chest CT may show pleural effusion, nodules, infiltrates, abscesses and cavitations.

Bacterial cultures taken from the blood, joint aspirates or other sites can identify the causative agent of the disease.

Other illnesses that can be included in the differential diagnosis are:

- Q fever

- Tuberculosis

- Pneumonia

Diagnosis is usually based on the symptoms. Medical imaging may be done to rule out complications. Medical imaging may include CT scan or MRI.

E.g.: stones, cholangiocarcinoma

E.g.: diverticulitis, appendicitis, Crohn's disease

E.g.: penetrating injury, iatrogenic (radiofrequency ablation)

A pyogenic liver abscess is a type of liver abscess caused by bacteria.

A computed tomography (CT) scan is the definitive diagnostic imaging test.

X-ray of the neck often (80% of the time) shows swelling of the retropharyngeal space in affected individuals. If the retropharyngeal space is more than half of the size of the C2 vertebra, it may indicate retropharyngeal abscess.

Diagnosis of anorectal abscess begins with a medical history and physical exam. Imaging studies which can help determine the diagnosis in cases of a deep non-palpable perirectal abscess include pelvic CT scan, MRI or trans-rectal ultrasound. These studies are not necessary, though, in cases which the diagnosis can be made upon physical exam.

1)positive tuberclin test

2)chest radiograph

3)CT scan

4)cytology/biopsy (FNAC)

5)AFB staining

6)mycobacterial culture

When properly diagnosed, the mortality of Lemierre's syndrome is about 4.6%. Since this disease is not well known and often remains undiagnosed, mortality might be much higher.

In someone suspected of having cholecystitis, blood tests are performed for markers of inflammation (e.g. complete blood count, C-reactive protein), as well as bilirubin levels in order to assess for bile duct blockage. Complete blood count typically shows an increased white blood count (12,000–15,000/mcL). C-reactive protein is usually elevated although not commonly measured in the United States. Bilirubin levels are often mildly elevated (1–4 mg/dL). If bilirubin levels are more significantly elevated, alternate or additional diagnoses should be considered such as gallstone blocking the common bile duct (common bile duct stone). Less commonly, blood aminotransferases are elevated. The degree of elevation of these laboratory values may depend on the degree of inflammation of the gallbladder.

Right upper quadrant abdominal ultrasound is most commonly used to diagnose cholecystitis. Ultrasound findings suggestive of acute cholecystitis include gallstones, fluid surrounding the gallbladder, gallbladder wall thickening (wall thickness over 3 mm), dilation of the bile duct, and sonographic Murphy's sign. Given its higher sensitivity, hepatic iminodiacetic acid (HIDA) scan can be used if ultrasound is not diagnostic. CT scan may also be used if complications such as perforation or gangrene are suspected.

The pus can be removed by a number of methods including needle aspiration, incision and drainage, and tonsillectomy.

Treatment can also be given while a patient is under anesthesia, but this is usually reserved for children or anxious patients. Tonsillectomy can be indicated if a patient has recurring peritonsillar abscesses or a history of tonsillitis. For patients with their first peritonsillar abscess most ENT-surgeons prefer to "wait and observe" before recommending tonsillectomy.

The diagnosis is established by a computed tomography (CT) (with contrast) examination. At the initial phase of the inflammation (which is referred to as cerebritis), the immature lesion does not have a capsule and it may be difficult to distinguish it from other space-occupying lesions or infarcts of the brain. Within 4–5 days the inflammation and the concomitant dead brain tissue are surrounded with a capsule, which gives the lesion the famous ring-enhancing lesion appearance on CT examination with contrast (since intravenously applied contrast material can not pass through the capsule, it is collected around the lesion and looks as a ring surrounding the relatively dark lesion). Lumbar puncture procedure, which is performed in many infectious disorders of the central nervous system is contraindicated in this condition (as it is in all space-occupying lesions of the brain) because removing a certain portion of the cerebrospinal fluid may alter the concrete intracranial pressure balances and causes the brain tissue to move across structures within the skull (brain herniation).

Ring enhancement may also be observed in cerebral hemorrhages (bleeding) and some brain tumors. However, in the presence of the rapidly progressive course with fever, focal neurologic findings (hemiparesis, aphasia etc.) and signs of increased intracranial pressure, the most likely diagnosis should be the brain abscess.

Raised inflammatory markers (high ESR, CRP) are common but nonspecific. Examination of the coughed up mucus is important in any lung infection and often reveals mixed bacterial flora. Transtracheal or transbronchial (via bronchoscopy) aspirates can also be cultured. Fiber optic bronchoscopy is often performed to exclude obstructive lesion; it also helps in bronchial drainage of pus.

Multiple imaging modalities may be necessary to evaluate abnormalities of the nipple-areolar complex.

In two studies performed in Japan, high-resolution MRI with a microscopy coil yielding 0.137-mm in-plane resolution has been used to confirm the presence of abscesses, isolated fistulas and inflammation and to reveal their position in order to guide surgery.

Periodontal abscesses may be difficult to distinguish from periapical abscesses. Since the management of a periodontal abscess is different from a periapical abscess, this differentiation is important to make (see Dental abscess#Diagnostic approach) For example, root canal therapy is unnecessary and has no impact on pain in a periodontal abscess.

RPA's frequently require surgical intervention. A tonsillectomy approach is typically used to access/drain the abscess, and the outcome is usually positive. Surgery in adults may be done without general anesthesia because there is a risk of abscess rupture during tracheal intubation. This could result in pus from the abscess aspirated into the lungs. In complex cases, an emergency tracheotomy may be required to prevent upper airway obstruction caused by edema in the neck.

High-dose intravenous antibiotics are required in order to control the infection and reduce the size of the abscess prior to surgery.

Chronic retropharyngeal abscess is usually secondary to tuberculosis and the patient needs to be started on anti-tubercular therapy as soon as possible.

Anal abscesses are rarely treated with a simple course of antibiotics. In almost all cases surgery will need to take place to remove the abscess. Treatment is possible in an emergency room under local anesthesia, but it is highly preferred to be formally admitted to a hospital and to have the surgery performed in an operating room under general anesthesia.

Generally speaking, a fairly small but deep incision is performed close to the root of the abscess. The surgeon will allow the abscess to drain its exudate and attempt to discover any other related lesions in the area. This is one of the most basic types of surgery, and is usually performed in less than thirty minutes by the anal surgical team. Generally, a portion of the exudate is sent for microbiological analysis to determine the type of infecting bacteria. The incision is not closed (stitched), as the damaged tissues must heal from the inside toward the skin over a period of time.

The affected individual is often sent home within twenty-four hours of the surgery, and may be instructed to perform several 'sitz baths' per day, whereby a small basin (which usually fits over a toilet) is filled with warm water (and possibly, salts) and the affected area is soaked for a period of time. Another method of recovery involves the use of surgical packing, which is initially inserted by the surgical team, with redressing generally performed by hospital staff or a District Nurse (however, following the results of several double-blind studies, the effectiveness of surgical packing has come into question). During the week following the surgery, many patients will have some form of antibiotic therapy, along with some form of pain management therapy, consistent with the nature of the abscess.

The patient usually experiences an almost complete relief of the severe pain associated to his/her abscess upon waking from anesthesia; the pain associated with the opening and draining incision during the post-operative period is often mild in comparison.

Death occurs in about 10% of cases and people do well about 70% of the time. This is a large improvement from the 1960s due to improved ability to image the head, better neurosurgery and better antibiotics.

Genitourinary amoebiasis or renal amoebiasis is a rare complication to amoebic liver abscess, which in turn is a complication of amoebiasis. It is believed to result from liver abscesses breaking open, whereupon the amoebas spread through the blood to the new locale. Genital involvement is thought to result from fistula formation from the liver or through rectocolitis. The involvement causes lesions which exude a high degree of pus.