A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations. It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries. More structured approaches are being increasingly used to measure levels of mental illness. HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts. In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity.
An air rim of 2 cm means that the pneumothorax occupies about 50% of the hemithorax. British professional guidelines have traditionally stated that the measurement should be performed at the level of the hilum (where blood vessels and airways enter the lung) with 2 cm as the cutoff, while American guidelines state that the measurement should be done at the apex (top) of the lung with 3 cm differentiating between a "small" and a "large" pneumothorax. The latter method may overestimate the size of a pneumothorax if it is located mainly at the apex, which is a common occurrence. The various methods correlate poorly but are the best easily available ways of estimating pneumothorax size. CT scanning (see below) can provide a more accurate determination of the size of the pneumothorax, but its routine use in this setting is not recommended.Not all pneumothoraces are uniform; some only form a pocket of air in a particular place in the chest. Small amounts of fluid may be noted on the chest X-ray (hydropneumothorax); this may be blood (hemopneumothorax). In some cases, the only significant abnormality may be the "deep sulcus sign", in which the normally small space between the chest wall and the diaphragm appears enlarged due to the abnormal presence of fluid. Computed tomography
A CT scan is not necessary for the diagnosis of pneumothorax, but it can be useful in particular situations.