If there is a well-founded suspicion of the presence of lung fibrosis, a range of investigations are necessary. It is important to take a very thorough history (questioning of the patient). In particular, this provides important information on what triggered the disease, e.g. through inhaled inorganic or organic dusts or medicines.
Questionnaires such as the Frankfurt Questionnaire, or the patient questionnaire used in the European IPF Registry may be helpful in this. These questionnaires cover all relevant aspects of the possible causes of lung and airways diseases, such as, in particular, contact with animals, occupational, family, drug, housing and environmental history.
Costly clinical and laboratory investigations (e.g. determination of rheumatoid factor or immunological investigations) are also generally necessary.
The basic diagnostic investigations include:
- physical examination
- lung function tests (with body plethysmography [measurement of lung function in a cabin resembling a telephone box], measurement of CO diffusion [measures how well oxygen from the air gets into the bloodstream via the alveoli] and analysis of capillary blood gases [determination of the blood oxygen and carbon dioxide content])
- X-ray of the lung/high-resolution computed tomography
In the early stage of the disease, there may be no changes in lung function and X-ray findings, a fact that often leads to delay in making the diagnosis.
Among the clinical investigation methods, only the measurement of CO diffusion and so-called ergospirometry [measurement of lung function under stress] are sensitive enough to be able to reliably exclude the presence of lung fibrosis.
The situation is similar regarding imaging investigations; the X-ray is one of the first investigations. X rays are able to pass through fibrotically changed tissue to only a limited extent with the result that the X-ray film is not as black and therefore “whiter” than normal lung tissue at these sites. However, the X-ray may be unremarkable in up to 10% of patients with lung fibrosis or may not be specific for lung fibrosis. Thus, in most cases, a computed tomography (CT) scan of the lung is needed as a further investigation. It has the advantage of giving images that are not superimposed. From the point of view of technology, a high-resolution (so-called HRCT) scan should be performed for this. Compared to the clinical investigation findings, only after an HRCT has been performed is it possible to reliably exclude fibrosing lung disease.
In order to determine the cause and classify the lung fibrosis, in many cases a bronchoscopy (lung endoscopy) is also recommendable[D1] . During this procedure, bronchoalveolar lavage (BAL: rinsing an individual lung segment with saline), a differential cell count (examination of individual cells), a microbiological examination (examination for organisms and pathogens in the lung) and transbronchial as well as mucosal biopsies (removal of a sample of tissue from different parts of the lung using a small pair of forceps) are performed.
In quite a number of cases, a definitive diagnosis is not possible even despite the above-mentioned investigations, so removal of a larger tissue specimen is needed. In most cases, a minimally invasive procedure in the form of so-called video-assisted thoracoscopy (VATS) is undertaken. This procedure is now associated with a very low complication rate and in most cases allows reliable evaluation of the disease process.
The diagnosis cannot currently be made only based on so-called surrogate parameters (e.g. blood tests). However, these tests can result in important additional information that shows an association between the lung disease and another disease, for example.
Parameters to monitor the course of the disease are regular lung function tests, blood tests, stress tests and radiological investigations.
Given the complexity of the disease syndrome, the definitive diagnosis of lung fibrosis should be made through discussion between experienced lung specialists, pathologists and radiologists, following the recommendation of the American Thoracic Society (ATS) and the European Respiratory Society (ERS). In case of specific issues, it is worth consulting a specialist in occupational medicine. The diagnosis can be established with the best-possible reliability based on current knowledge only through interdisciplinary cooperation in the diagnostic process. Sometimes, however, even the
diagnosis made as part of such a collaborative discussion has a provisional nature as, for example, new aspects may be discovered after further diagnostic procedures. Also in the case of very advanced change in the lung tissue, it is sometimes no longer possible to reliably classify the changes. The doctors and hospitals participating in the European IPF network hold such interdisciplinary discussions at regular intervals.