Chest radiography is the preferred means of initial diagnosis for hemothorax. Upright radiography is preferred but supine films may be taken when upright radiography is not feasible due to the clinical situation. Tube thoracostomy may be done prior to imaging when patients have sustained blunt or penetrating thoracic trauma and display unstable hemodynamics, have respiratory failure with absent or decreased breath sounds, show tracheal deviation, or have serious penetrating injuries. In upright radiography, hemothorax is suggested by blunting of the costophrenic angle or partial or complete opacification of the hemithorax, in which the lateral side of the chest appears bright and the lung appears pushed away toward the center; the air-filled lung normally appears as a dark space on radiographic film. In the case of a small hemothorax, several hundred milliliters of blood can be hidden by the diaphragm and abdominal viscera. In supine patients, signs of hemothorax may also be subtle on radiographic film, because the blood will layer in the pleural space, and can be seen as a haziness in one half of the thorax relative to the other side.

Ultrasonography is also used for detection of hemothorax and other pleural effusions, particularly in the critical care and trauma settings, because it provides rapid, reliable results in order to make a diagnosis in an emergency situation. Computed tomography (CT or CAT) scans can detect much smaller amounts of fluid than chest radiography, but computed tomography is not a primary method of diagnosis within the trauma setting, due to the time required for imaging, the requirement that a patient remain supine, and the need to transport a critically ill patient to the scanner.

Once a pleural effusion is diagnosed, its cause must be determined. Pleural fluid is drawn out of the pleural space in a process called thoracentesis, and it should be done in almost all patients who have pleural fluid that is at least 10 mm in thickness on CT, ultrasonography, or lateral decubitus X-ray and that is new or of uncertain etiology. In general, the only patients who do not require thoracentesis are those who have heart failure with symmetric pleural effusions and no chest pain or fever; in these patients, diuresis can be tried, and thoracentesis is avoided unless effusions persist for more than 3 days. In a thoracentesis, a needle is inserted through the back of the chest wall in the sixth, seventh, or eighth intercostal space on the midaxillary line, into the pleural space. The use of ultrasound to guide the procedure is now standard of care as it increases accuracy and decreases complications. After removal, the fluid may then be evaluated for:

1. Chemical composition including protein, lactate dehydrogenase (LDH), albumin, amylase, pH, and glucose

2. Gram stain and culture to identify possible bacterial infections

3. White and red blood cell counts and differential white blood cell counts

4. Cytopathology to identify cancer cells, but may also identify some infective organisms

5. Other tests as suggested by the clinical situation – lipids, fungal culture, viral culture, tuberculosis cultures, lupus cell prep, specific immunoglobulins

Definitions of the terms "transudate" and "exudate" are the source of much confusion. Briefly, transudate is produced through pressure filtration without capillary injury while exudate is "inflammatory fluid" leaking between cells.

Transudative pleural effusions are defined as effusions that are caused by "systemic" factors that alter the pleural equilibrium, or Starling forces. The components of the Starling forces–hydrostatic pressure, permeability, and oncotic pressure (effective pressure due to the composition of the pleural fluid and blood)–are altered in many diseases, e.g., left ventricular failure, kidney failure, liver failure, and cirrhosis. Exudative pleural effusions, by contrast, are caused by alterations in "local" factors that influence the formation and absorption of pleural fluid (e.g., bacterial pneumonia, cancer, pulmonary embolism, and viral infection).

An accurate diagnosis of the cause of the effusion, transudate versus exudate, relies on a comparison of the chemistries in the pleural fluid to those in the blood, using Light's criteria. According to Light's criteria (Light, et al. 1972), a pleural effusion is likely exudative if at least one of the following exists:

1. The ratio of pleural fluid protein to serum protein is greater than 0.5

2. The ratio of pleural fluid LDH and serum LDH is greater than 0.6

3. Pleural fluid LDH is greater than 0.6 or times the normal upper limit for serum. Different laboratories have different values for the upper limit of serum LDH, but examples include 200 and 300 IU/l.

The sensitivity and specificity of Light's criteria for detection of exudates have been measured in many studies and are usually reported to be around 98% and 80%, respectively. This means that although Light's criteria are relatively accurate, twenty percent of patients that are identified by Light's criteria as having exudative pleural effusions actually have transudative pleural effusions. Therefore, if a patient identified by Light's criteria as having an exudative pleural effusion appears clinically to have a condition that usually produces transudative effusions, additional testing is needed. In such cases, albumin levels in blood and pleural fluid are measured. If the difference between the albumin level in the blood and the pleural fluid is greater than 1.2 g/dL (12 g/L), this suggests that the patient has a transudative pleural effusion. However, pleural fluid testing is not perfect, and the final decision about whether a fluid is a transudate or an exudate is based not on chemical analysis of the fluid, but on accurate diagnosis of the disease that produces the fluid.

The traditional definitions of transudate as a pleural effusion due to systemic factors and an exudate as a pleural effusion due to local factors have been used since 1940 or earlier (Light et al., 1972). Previous to Light's landmark study, which was based on work by Chandrasekhar, investigators unsuccessfully attempted to use other criteria, such as specific gravity, pH, and protein content of the fluid, to differentiate between transudates and exudates. Light's criteria are highly statistically sensitive for exudates (although not very statistically specific). More recent studies have examined other characteristics of pleural fluid that may help to determine whether the process producing the effusion is local (exudate) or systemic (transudate). The chart to the right, illustrates some of the results of these more recent studies. However, it should be borne in mind that Light's criteria are still the most widely used criteria.

The Rational Clinical Examination Series review found that bilateral effusions, symmetric and asymmetric, are the most common distribution in heart failure (60% of effusions in heart failure will be bilateral). When there is asymmetry in heart failure-associated pleural effusions (either unilateral or one side larger than the other), the right side is usually more involved than the left.

Instruments in picture while in shape are accurate most hospitals use disposable trocar's as they are safer since they are always sharp since they are single use and have a much smaller risk of cross patient contamination.

A hemothorax is managed by removing the source of bleeding and by draining the blood already in the thoracic cavity. Blood in the cavity can be removed by inserting a drain (chest tube) in a procedure called a tube thoracostomy. Generally, the thoracostomy tube is placed between the ribs in the sixth or seventh intercostal space at the mid-axillary line. Usually the lung will expand and the bleeding will stop after a chest tube is inserted.

The blood in the chest can thicken as the clotting cascade is activated when the blood leaves the blood vessels and comes into contact with the pleural surface, injured lung or chest wall, or with the chest tube. As the blood thickens, it can clot in the pleural space (leading to a retained hemothorax) or within the chest tube, leading to chest tube clogging or occlusion. Chest tube clogging or occlusion can lead to worse outcomes as it prevents adequate drainage of the pleural space, contributing to the problem of retained hemothorax. In this case, patients can be hypoxic, short of breath, or in some cases, the retained hemothorax can become infected (empyema).

Retained hemothorax occurs when blood remains in the pleural space, and is a risk factor for the development of complications, including the accumulation of pus in the pleural space and fibrothorax. It is treated by inserting a second chest tube or by drainage by video-assisted thoracoscopy. Fibrolytic therapy has also been studied as a treatment.

When hemothorax is treated with a chest tube, it is important that it maintain its function so that the blood cannot clot in the chest or the tube. If clogging occurs, internal chest tube clearing can be performed using an open or closed technique. Manual manipulation, which may also be called milking, stripping, or tapping, of chest tubes is commonly performed to maintain an open tube, but no conclusive evidence has demonstrated that any of these techniques are more effective than the others, or that they improve chest tube drainage.

In some cases bleeding continues and surgery is necessary to stop the source of bleeding. For example, if the hemothorax was caused by aortic rupture in high energy trauma, surgical intervention is mandatory.

Fibrothorax is diffuse fibrosis of the pleural space surrounding the lungs. It can have several causes including hemothorax, pleural effusion and tuberculosis. It may also be induced by exposure to certain substances, as with asbestos-induced diffuse pleural fibrosis. Idiopathic fibrothorax may also occur.

In fibrothorax, scar tissue is formed around the visceral pleura following inflammation due to pleural effusion or other pathology. The scar tissue lies in a sheet between the pleura, then fuses with the parietal pleura and the chest wall. Over time, generally the course of years, the fibrotic scar tissue slowly tightens, which results in the contraction of the entire hemithorax, and leaves the ribs immobilized. Within the chest, the lung is compressed and unable to expand, making it vulnerable to collapse. At the microscopic level, the scar tissue is composed of collagen fibers deposited in a basket weave pattern. The treatment for fibrothorax is decortication, the surgical removal of the fibrous layer of scar tissue. However, since many of the diseases and conditions resulting in fibrothorax are treatable, prevention remains the preferred method of managing fibrothorax.