The current clinical case definition of diphtheria used by the United States' Centers for Disease Control and Prevention is based on both laboratory and clinical criteria.

Empirical treatment should generally be started in a patient in whom suspicion of diphtheria is high.

Many cases of croup have been prevented by immunization for influenza and diphtheria. At one time, croup referred to a diphtherial disease, but with vaccination, diphtheria is now rare in the developed world.

The most commonly used system for classifying the severity of croup is the Westley score. It is primarily used for research purposes rather than in clinical practice. It is the sum of points assigned for five factors: level of consciousness, cyanosis, stridor, air entry, and retractions. The points given for each factor is listed in the adjacent table, and the final score ranges from 0 to 17.

- A total score of ≤ 2 indicates "mild" croup. The characteristic barking cough and hoarseness may be present, but there is no stridor at rest.

- A total score of 3–5 is classified as "moderate" croup. It presents with easily heard stridor, but with few other signs.

- A total score of 6–11 is "severe" croup. It also presents with obvious stridor, but also features marked chest wall indrawing.

- A total score of ≥ 12 indicates impending respiratory failure. The barking cough and stridor may no longer be prominent at this stage.

85% of children presenting to the emergency department have mild disease; severe croup is rare (<1%).

The diagnosis of group A beta-hemolytic streptococcus (GABHS) tonsillitis can be confirmed by culture of samples obtained by swabbing both tonsillar surfaces and the posterior pharyngeal wall and plating them on sheep blood agar medium. The isolation rate can be increased by incubating the cultures under anaerobic conditions and using selective growth media. A single throat culture has a sensitivity of 90–95% for the detection of GABHS (which means that GABHS is actually present 5–10% of the time culture suggests that it is absent). This small percentage of false-negative results are part of the characteristics of the tests used but are also possible if the patient has received antibiotics prior to testing. Identification requires 24 to 48 hours by culture but rapid screening tests (10–60 minutes), which have a sensitivity of 85–90%, are available. Older antigen tests detect the surface Lancefield group A carbohydrate. Newer tests identify GABHS serotypes using nucleic acid (DNA) probes or polymerase chain reaction. Bacterial culture may need to be performed in cases of a negative rapid streptococcal test.

True infection with GABHS, rather than colonization, is defined arbitrarily as the presence of >10 colonies of GABHS per blood agar plate. However, this method is difficult to implement because of the overlap between carriers and infected patients. An increase in antistreptolysin O (ASO) streptococcal antibody titer 3–6 weeks following the acute infection can provide retrospective evidence of GABHS infection and is considered definitive proof of GABHS infection.

Increased values of secreted phospholipase A2 and altered fatty acid metabolism in patients with tonsillitis may have diagnostic utility.

It is hard to differentiate a viral and a bacterial cause of a sore throat based on symptoms alone. Thus often a throat swab is done to rule out a bacterial cause.

The modified Centor criteria may be used to determine the management of people with pharyngitis. Based on 5 clinical criteria, it indicates the probability of a streptococcal infection.

One point is given for each of the criteria:

- Absence of a cough

- Swollen and tender cervical lymph nodes

- Temperature >

- Tonsillar exudate or swelling

- Age less than 15 (a point is subtracted if age >44)

The McIsaac criteria adds to the Centor:

- Age less than 15: add one point

- Age greater than 45: subtract one point

The Infectious Disease Society of America however recommends against empirical treatment and considers antibiotics only appropriate following positive testing. Testing is not needed in children under three as both group A strep and rheumatic fever are rare, except if they have a sibling with the disease.

Treatments to reduce the discomfort from tonsillitis include:

- pain and fever reducing medications such as paracetamol (acetaminophen) and ibuprofen

- warm salt water gargle, lozenges, or warm liquids

When tonsillitis is caused by a virus, the length of illness depends on which virus is involved. Usually, a complete recovery is made within one week; however, symptoms may last for up to two weeks.

A diagnosis can be made from clinical signs and symptoms, and treatment consists of minimizing the discomfort of symptoms. It can be differentiated from herpetic gingivostomatitis by the positioning of vesicles - in herpangina, they are typically found on the posterior oropharynx, as compared to gingivostomatitis where they are typically found on the anterior oropharynx and the mouth.

The tests, called assays, for detection of virus infection involve serum or blood tests that detect either viral antigens (proteins produced by the virus) or antibodies produced by the host. Interpretation of these assays is complex.

The surface antigen (HBsAg) is most frequently used to screen for the presence of this infection. It is the first detectable viral antigen to appear during infection. However, early in an infection, this antigen may not be present and it may be undetectable later in the infection as it is being cleared by the host. The infectious virion contains an inner "core particle" enclosing viral genome. The icosahedral core particle is made of 180 or 240 copies of the core protein, alternatively known as core antigen, or HBcAg. During this 'window' in which the host remains infected but is successfully clearing the virus, IgM antibodies specific to the core antigen ("anti-HBc IgM") may be the only serological evidence of disease. Therefore, most diagnostic panels contain HBsAg and total anti-HBc (both IgM and IgG).

Shortly after the appearance of the HBsAg, another antigen called e antigen (HBeAg) will appear. Traditionally, the presence of HBeAg in a host's serum is associated with much higher rates of viral replication and enhanced infectivity; however, variants of the virus do not produce the 'e' antigen, so this rule does not always hold true. During the natural course of an infection, the HBeAg may be cleared, and antibodies to the 'e' antigen ("anti-HBe") will arise immediately afterwards. This conversion is usually associated with a dramatic decline in viral replication.

If the host is able to clear the infection, eventually the HBsAg will become undetectable and will be followed by IgG antibodies to the surface antigen and core antigen ("anti-HBs" and "anti HBc IgG"). The time between the removal of the HBsAg and the appearance of anti-HBs is called the window period. A person negative for HBsAg but positive for anti-HBs either has cleared an infection or has been vaccinated previously.

Individuals who remain HBsAg positive for at least six months are considered to be carriers. Carriers of the virus may have chronic hepatitis B, which would be reflected by elevated serum alanine aminotransferase (ALT) levels and inflammation of the liver, if they are in the immune clearance phase of chronic infection. Carriers who have seroconverted to HBeAg negative status, in particular those who acquired the infection as adults, have very little viral multiplication and hence may be at little risk of long-term complications or of transmitting infection to others.

PCR tests have been developed to detect and measure the amount of HBV DNA, called the viral load, in clinical specimens. These tests are used to assess a person's infection status and to monitor treatment. Individuals with high viral loads, characteristically have ground glass hepatocytes on biopsy.

Treatment is usually supportive only, as the disease is self-limiting and usually runs its course in less than a week.

Gargling salt water is often suggested but evidence looking at its usefulness is lacking. Alternative medicines are promoted and used for the treatment of sore throats. However, they are poorly supported by evidence.

A number of different tests are available to determine the degree of cirrhosis present. Transient elastography (FibroScan) is the test of choice, but it is expensive. Aspartate aminotransferase to platelet ratio index may be used when cost is an issue.

During the latest outbreak of the disease (2004), several treatment methods were tested. Main treatment involved the administration of antibiotics, in some cases glucose solution or dietary mixtures were additionally supplemented. Outcome of the different treatment methods varied greatly. Especially the success of antibiotic treatment and a widespread use on wild animals remains a matter of debate.

In eosinophilic myocarditis, echocardiography typically gives non-specific and only occasional findings of endocardium thickening, left ventricular hypertrophy, left ventricle dilation, and involvement of the mitral and/or tricuspid valves. However, in acute necrotizing eosinophilic myocarditis, echocardiography usually gives diagnostically helpful evidence of a non-enlarged heart with a thickened and poorly contracting left ventricle. Gadolinium-based cardiac magnetic resonance imaging is the most useful non-invasive procedure for diagnosing eosinophilic myocarditis. It supports this diagnosis if it shows at least two of the following abnormalities: a) an increased signal in T2-weighted images; b) an increased global myocardial early enhancement ratio between myocardial and skeletal muscle in enhanced T1 images and c) one or more focal enhancements distributed in a non-vascular pattern in late enhanced T1-weighted images. Additionally, and unlike in other forms of myocarditis, eosinophilic myocarditis may also show enhanced gadolinium uptake in the sub-endocardium. However, the only definitive test for eosinophilic myocarditis in cardiac muscle biopsy showing the presence of eosinophilic infiltration. Since the disorder may be patchy, multiple tissue samples taken during the procedure improve the chances of uncovering the pathology but in any case negative results do not exclude the diagnosis.

Diphtheritic stomatitis is a recently discovered disease and has thus far been reported only in Yellow-eyed penguins ("Megadyptes antipodes"). Its symptoms are similar to human diphtheria and is characterized by infecteous lesions in the mouth area that impede swallowing and cause respiratory troubles. The infection is caused by "Corynebacterium amycolatum", an aerobic Gram-positive bacterium and mainly affects very young chicks. However, it seems likely that a triggering agent (e.g. a virus) might be involved in which renders the corynebacterium a secondary pathogen.

The disease has been a serious cause of mortality in the 2002 and 2004 Yellow-eyed penguin breeding seasons. It seems that only the New Zealand South Island and Stewart Island/Rakiura were affected.

The diagnosis of Ludwig's angina is clinical. History and physical examination are usually enough to establish the diagnosis.

The prognosis of eosinophilic myocarditis is anywhere from rapidly fatal to extremely chronic or non-fatal. Progression at a moderate rate over many months to years is the most common prognosis. In addition to the speed of inflammation-based heart muscle injury, the prognosis of eosinophilc myocarditis may be dominated by that of its underlying cause. For example, an underlying malignant cause for the eosinophilia may be survival-limiting.

There are various risk assessment systems for determining the risk of coronary artery disease, with various emphasis on different variables above. A notable example is Framingham Score, used in the Framingham Heart Study. It is mainly based on age, gender, diabetes, total cholesterol, HDL cholesterol, tobacco smoking and systolic blood pressure.

Diagnosis is usually clinical. Smear for fusospirochaetal bacteria and leukocytes; blood picture occasionally. The important differentiation is with acute leukaemia or herpetic stomatitis.

Treatment involves appropriate antibiotic medications, monitoring and protection of the airway in severe cases, and, where appropriate, urgent Otolaryngology-Head and Neck Surgery, maxillo-facial surgery and/or dental consultation to incise and drain the collections. The antibiotic of choice is from the penicillin group.

Incision and drainage of the abscess may be either intraoral or external. An intraoral incision and drainage procedure is indicated if the infection is localized to the sublingual space. External incision and drainage is performed if infection involves the perimandibular spaces.

A nasotracheal tube is sometimes warranted for ventilation if the tissues of the mouth make insertion of an oral airway difficult or impossible.

In cases where the patency of the airway is compromised, skilled airway management is mandatory. Fiberoptic intubation is common.

Ludwig's angina is a life-threatening condition, and carries a fatality rate of about 5%.

The diagnosis of plastic bronchitis is confirmed by recovery of casts that have been coughed up or visualized during a bronchoscopy. There is no specific cytologic, pathologic or laboratory test that is diagnostic for casts due to lymphatic PB.

Simple chest roentenograms may reveal collapse due to airway obstruction. The contralateral lung may be hyperinflated. Casts can be visualized within the major airways using computerized axial tomography scans.

Heavy T2-weighted MRI, and, as appropriate, intranodal lymphangiogram and/or dynamic contrast-enhanced MR lymphangiography may be useful for identifying pathological lymphatic tissue and/or lymphatic flow.

Treatment includes irrigation and debridement of necrotic areas (areas of dead and/or dying gum tissue), oral hygiene instruction and the uses of mouth rinses and pain medication. If there is systemic involvement, then oral antibiotics may be given, such as metronidazole. As these diseases are often associated with systemic medical issues, proper management of the systemic disorders is appropriate.

Diagnosis of acute coronary syndrome generally takes place in the emergency department, where ECGs may be performed sequentially to identify "evolving changes" (indicating ongoing damage to the heart muscle). Diagnosis is clear-cut if ECGs show elevation of the "ST segment", which in the context of severe typical chest pain is strongly indicative of an acute myocardial infarction (MI); this is termed a STEMI (ST-elevation MI), and is treated as an emergency with either urgent coronary angiography and percutaneous coronary intervention (angioplasty with or without stent insertion) or with thrombolysis ("clot buster" medication), whichever is available. In the absence of ST-segment elevation, heart damage is detected by cardiac markers (blood tests that identify heart muscle damage). If there is evidence of damage (infarction), the chest pain is attributed to a "non-ST elevation MI" (NSTEMI). If there is no evidence of damage, the term "unstable angina" is used. This process usually necessitates admission to hospital, and close observation on a coronary care unit for possible complications (such as cardiac arrhythmias – irregularities in the heart rate). Depending on the risk assessment, stress testing or angiography may be used to identify and treat coronary artery disease in patients who have had an NSTEMI or unstable angina.

Nephrotoxicity is usually monitored through a simple blood test. A decreased creatinine clearance indicates poor renal function. Normal creatinine level is between 80 - 120 μmol/L. In interventional radiology, a patient's creatinine clearance levels are all checked prior to a procedure.

Serum creatinine is another measure of renal function, which may be more useful clinically when dealing with patients with early kidney disease.