It is described as any loss or abnormality of psychological, physiological or anatomical structure or function. It is equivalent to disease and as such is treated as a strictly medical concept. This loss of function or a disease does not necessarily mean incapacity, as other factors, such as the effort demanded by the type of work, come into consideration. Thus, for example, mild emphysema does not affect the fitness for work of an office worker. Evaluation of the dysfunction caused by the respiratory disease is the main objective of these recommendations.

This is the effect of the impairment on the patient's life. Incapacity for work would transfer the repercussion of the disease onto work performance. This concept takes into account that the same degree of functional involvement may have different consequences for different individuals, depending on other variables such as sex, age or type of work. For example, someone with moderate COPD may be able to carry out office work but if the patient is a fireman, it may lead to incapacity for work. To establish this concept, it is essential to have knowledge of the disease and to analyze the job in question. The legal or administrative aspects are also taken into account and accompanied by a financial payment. These are the two concepts involved in the evaluation of fitness for work.

This is a generic term which includes deficits, limitations in activity and restrictions in social life. It is not used in the evaluation of fitness for work of the individual. It indicates the disadvantage or handicap that may be involved for the person suffering the disease. In the Spanish state, the evaluation of the disability, expressed in a percentage, is carried out by applying scales established in a Royal Decree (Law).5 The possible benefits for patients with a recognized degree of disability include the following6: measures for promoting employment, adaptation of the job, adaptation of selection tests for accessing public employment, grants for rehabilitation treatments, accessibility and adaptation of the home, etc. These benefits are sufficiently significant for it to be important for an individual with disability to seek an appropriate evaluation.

Disability and incapacity for work are different concepts, and do not always coincide. For example, the amputation of a little finger might cause a mild disability but for a pianist, it could mean incapacity for work; in contrast, persons with severe disabilities, such as paraplegia, loss of sight, etc., may be able to do certain types of work.

Causes a reduction of ≥33% in normal capacity for performing the worker's usual profession, but he/she may be able to carry out the basic tasks of the job.

The worker is incapable of carrying out all the basic tasks of his/her profession, but could do another job with fewer physical requirements, or, depending on the case, one in which he/she is not exposed to a certain substance or product.

Recognizes that it is impossible for the patient to carry out any type of job. The benefit will be equivalent to 100% of the patient's calculated basic wage.

This is the situation of a worker affected by PI who requires the assistance of other people for the most basic life functions. The benefits will include payment for that person. The right to payment for PI derived by common disease will not be recognized for anyone aged 65 years or older.

Chronic diseases which involve a sustained loss of function, in spite of the patient having received the appropriate treatment, can lead to PI (Table 2). The disease must be certified using objective tests and this process must include the performance of at least a clinical history, work history, physical examination, chest X-ray and lung function tests.

Clinical history: In addition to the data necessary for carrying out the disease diagnosis, smoking history, frequency of exacerbations and possible hospitalizations during the course of the disease, chronic treatment and the existence of other associated diseases must be determined. It must be taken into account that dyspnea and a sensation of difficulty exercising are subjective concepts that cannot be used in an isolated manner as parameters for evaluating functional capacity.11Work history must be comprehensive, detailing the characteristics of the job, energy requirements involved and the climatic conditions in which it is performed, exposure to irritants and timetables with possible shiftwork. The determination of these data is indispensable in evaluating the effect of the job on the disease and for issuing appropriate advice. A physical examination, paying particular attention to the respiratory tract and the heart, provides valuable data on respiratory rate, cyanosis, nail clubbing, edemas, etc. Chest X-ray is more useful for diagnosing the disease than for establishing the degree of functional involvement. Even in interstitial diseases, there is a weak correlation between the image and functional changes.12 Computed tomography (CT) of the chest has a fundamental role in the study of diffuse interstitial lung diseases, in emphysema [forced expiratory volume in one second (FEV1) and diffusing capacity are well correlated with the extent of emphysema],13 and in bronchiectasis.

The degree of functional involvement must be evaluated when, once all the possible treatment resources have been applied, the patient has reached a stable phase of more than 6 months’ duration. The degree of pulmonary dysfunction is always expressed in comparison with reference values obtained in a healthy population. It is important to remember that pulmonary dysfunction does not necessarily imply incapacity for work, but is one of the factors (very important but not the only one) involved in the complex concept of incapacity for work. The classic techniques are spirometry, lung volume testing and carbon monoxide diffusing capacity (DLCO). However, in selected cases, it is not unusual to use arterial blood gases and exercise stress testing for a more specific definition. Moreover, other specific studies such as bronchial challenge tests or sleep studies may be necessary for individuals with certain jobs.

Spirometry is the test with the most practical significance for the study of lung function. The most useful variables are forced vital capacity (FVC), FEV1 and the relation between them. They have been selected because the degree of involvement is easy to interpret and they are highly reproducible. Other less standardized spirometry tests with greater variability, such as mid and end-expiratory flows, are not recommended.14 The collaboration of the subject is so important that for results to be correctly interpreted, the acceptability and reproducibility criteria of the curves, analysis of results, reference values and other technical aspects must be closely followed. The test must be carried out according to the standards of the SEPAR (Spanish Society of Pulmonology and Thoracic Surgery) guidelines.15 Spirometry allows the appropriate diagnosis and direct quantification of most obstructive disorders. However, the diagnosis of restrictive disorders is based on a reduction in total lung capacity (TLC), which requires specific techniques (plethysmography, helium dilution or nitrogen washout). Using a reduction in FVC for the diagnosis is inappropriate because it is not pathognomonic of restrictive changes and FVC can be reduced due to many conditions, including the airway obstruction itself. DLCO provides information on the anatomical and functional integrity of gas exchange via the alveolar-capillary membrane. The single breath test is the technique of choice, and should be carried out in strict compliance with the technical guidelines, after a minimum period of 6–8h without smoking, before the use of a bronchodilator, after a period of rest and taking into account all the factors involved (hemoglobin, etc.). Its reproducibility is lower, with an inter-operator variability of 5%–10%, and even greater variability has been observed among different lung function laboratories.16 The study by Cotes et al.17 has been the reference for establishing fitness for work scales, depending on the values of the spirometry and diffusing capacity data.

Chronic respiratory failure may be due to extrathoracic causes (changes in respiratory control, drugs, metabolic changes), neuromuscular disease or changes in the chest wall, or may be caused by lung diseases (bronchial, interstitial or vascular). Regardless of its etiology, it is associated with symptoms, long-term effects and treatment which can frequently lead to incapacity for maintaining a working life. In all diseases in which it is suspected, it must be confirmed with a determination of arterial blood gases. As it is very variable, it should be documented on 2 occasions, one month apart. The correlation of arterial blood gases with functional changes and limitations in exercise capacity is variable and has not been proven.18 Arterial blood gases within normal values are not a symptom of a lack of severity, and the presence of hypoxemia at rest does not always imply limitations for work.

Resting functional tests provide partial information about the pulmonary response to exercise. Multiple factors are involved in the capacity for exercise in respiratory patients.19 This explains the disparity between ventilatory function and exercise stress capacity observed in various patient groups.20 Cases with severe involvement are generally unambiguous, but in patients with mild or moderate dysfunction who report exercise limitation, the ideal situation would be to determine the energy requirements of the job and carry out a maximum stress test in the laboratory. It should be remembered that most jobs have an energy output which varies over the course of the working day, and that over an 8-h day, an individual can sustain a level of activity which does not require more than 40%–50% of the maximum oxygen consumption (VO2max). Not all lung function laboratories are equipped to carry out stress testing, so some authors, in accordance with the results of several studies, propose estimating VO2max from the 6-min walk test, a sub-maximum stress test that correlates well with the capacity for performing activities of daily living and exercise tolerance and can be of prognostic use in some diseases.21,22 The causes of exercise limitation can be identified using stress tests.23

Although nocturnal polysomnography is the recommended method for establishing a definitive diagnosis of sleep apnea–hypopnea syndrome (SAHS), respiratory polygraphy is an acceptable alternative for making this diagnosis in patients with low or high clinical probability, although its most significant limitation is the lack of equipment validation. The equipment used must be validated for the specific task that is to be carried out in each sleep unit. The polysomnography study is indicated in borderline cases.24

An increasing amount of data are becoming available to support the hypothesis of systemic involvement in some chronic lung diseases. This involvement is not reflected in the classic parameters of the thoracic imaging and lung function tests, although it may affect quality of life and survival. The BODE index also collects body mass index as a determinant of survival in COPD patients.25 Various studies associate repeated exacerbations as a risk factor for poor disease prognosis26; this has been introduced in the most recent classifications.27 We must not forget that smoking, the degree of regular physical activity, drugs, personality and associated diseases will also influence exercise limitation in these patients.

Asthma is a chronic inflammatory disease, which presents with bronchial hyperresponsiveness and variable air flow obstruction which is totally or partially reversible, either spontaneously or with treatment.34 Over 25% of asthmatics have some period of incapacity for work throughout the year.35 The initial objective should be to confirm the diagnosis of asthma. In the additional examinations it will be necessary to show obstruction and/or bronchial hyperresponsiveness (BHR) with spirometry and bronchodynamic testing. Exhaled nitric oxide (FeNO) must be used with caution as a diagnostic tool.36 Asthma is a disease which varies over time, making it difficult to evaluate PI. The evaluation must be performed when the disease is stable and after treatment has been completed, on occasions after an exhaustive assessment using the same study methodology as for difficult-to-control asthma; an exercise stress test may even be necessary to allow the identification of cases of stress asthma, and to identify simulators or other concurrent aspects which may modify the course of the disease and its functional repercussions.37 The following must be taken into account for the evaluation of PI in asthma: (1) FEV1 value, compared to the theoretical value; (2) degree of reversibility in bronchodilator tests or (3) degree of BHR according to the bronchial challenge tests; (4) need for treatment; (5) degree of disease control.38,39 For the evaluation of asthma control, questionnaires such as the Asthma Control Test (ACT) have been developed that have been validated by placing cutoff points between different degrees of control.40 An association has also been found between the clinical control of asthma and the presence of eosinophils in sputum.41 The job performed by each specific patient will impact decisively on this evaluation. The joint use of the severity classification and control proposed by the ATS39 and by GINA35,42 is useful for establishing the degree of dysfunction (Table 4).

COPD is characterized by chronic, partially reversible obstruction of the airway, associated with an abnormal inflammatory response, essentially to tobacco smoke, and to other environmental factors to a lesser extent. In this disease, destruction of the alveolar spaces occurs concomitantly with loss of the elastic support of the lung and inflammatory narrowing with airway remodeling.43,44 These changes lead to an increase in pulmonary resistances with decreased respiratory flow, presence of hyperinflation and abnormal gas exchange. COPD is one of the most common causes of disability.31 The diagnosis of this heterogeneous disease is based on the presence of risk factors, clinical symptoms (cough, expectoration, dyspnea) and a FEV1/FVC ratio lower than 0.7 in the post-bronchodilator spirometry, as a criterion for airway obstruction.28 The diagnosis must be confirmed and the evaluation made after using all the recommended treatments, including respiratory rehabilitation. COPD assessment will include the determination of lung volumes and diffusing capacity, examinations which are particularly useful in emphysema, a common phenotype of this disease.45 Different factors are involved in the prognosis of patients with COPD, and a multidimensional evaluation is recommended, including all the other BODE index parameters26 (dyspnea, body mass index and exercise capacity with a 6-min walk test) and the frequency of episodes of exacerbation, according to the latest GOLD classification.28

Arterial blood gas determinations are indicated if FEV1 is less than 40%, oxyhemoglobin saturation is less than 95% or if cor pulmonale is suspected. Respiratory failure would be a PI criterion for any activity.46 VO2max must be determined in individuals with mild or moderate deterioration (GOLD stages 2 or 3), evaluating the results and physical burden of the job for determining fitness for work.47 The use of various questionnaires allows the presence of anxiety and depression,47 common in patients with COPD, and the impact of the disease on activities of daily living to be determined. Osteoporosis and musculoskeletal dysfunction are conditions that frequently appear alongside COPD and can impact on the quality of life and reduce fitness for work.48 A working environment with dust, smoke or irritants must be taken into account for suggesting a disability claim49 (Table 5)

Bronchiectasis is characterized by abnormal thickening of the bronchial wall with dilation of the bronchi, due to a vicious circle of transmural infection and inflammation with release of mediators. Diagnosis is made by high resolution computed tomography and the clinical symptoms can be variable. It usually presents with repeated respiratory infections, and between infectious episodes, the patients may be asymptomatic or have chronic expectoration. There may be bloody expectoration or relapsing hemoptysis, clinical signs and symptoms of bronchial hyperreactiveness, dyspnea (depending on the degree of lung function involvement), pleuritic chest pain due to involvement of the visceral pleura, asthenia and weight loss.50 The presence and etiology of bacterial colonization impacts prognosis and severity.51 Changes in lung function will limit fitness for work to the same degree as other chronic diseases, but the limitations that might interfere in the subject's daily activity, e.g. colonization, infectious and non-infectious complications, such as relapsing hemoptysis, the need for continuous, long-term treatment, such as physiotherapy or inhaled antibiotics and the subject's nutritional status, must also be taken into account. Accordingly, even if a significant deterioration in lung function coexists in patients with extensive locations, this is not always the limiting factor for the patient's daily life. Colonization and bronchopulmonary infections must be medically documented, and the clinical situation has to be maintained for one year for the evaluation to be carried out.

If bronchiectasis is caused by cystic fibrosis of the pancreas, in addition to lung dysfunction, the involvement of other systems and organs (gastrointestinal, endocrine, metabolic, bone) will be considered for the fitness for work assessment.

For the assessment of fitness for work in the cancer patient, other parameters associated with the state of health, remission and survival prognosis, in addition to lung function, must be taken into account. The Karnofsky score has been shown to be a useful tool for the global determination of the functional status of cancer patients, for predicting their progress and survival and as an indicator of quality of life with lung cancer.52,53 Patients with a Karnofsky score of less than 80, those with an anatomical extension higher than stage II on the TNM classification54 at the time of diagnosis or who have required a pneumonectomy, and patients requiring maintenance chemotherapy are generally and empirically considered unable to work, regardless of their lung function, for jobs involving moderate effort.

Some jobs require a high degree of alertness and have a high risk of accidents, and SAHS may increase the risk. To determine the capacity of the subject for carrying out this work, the symptoms, particularly excessive daytime sleepiness, will be evaluated and therapeutic compliance with CPAP treatment, which should be analyzed with a timer, will be determined. In principle, a patient who is following the treatment correctly and does not have any residual symptoms should be considered able to work.55 In the special case of drivers, the regulations for obtaining or extending a driving license, with a maximum term of validity of 1 or 2 years, state that “persons suffering obstructive sleep apnea syndrome or related disorders, require a report from a Sleep Unit declaring that they are undergoing treatment and monitoring of daytime symptoms”.56

Pulmonary hypertension (PH) is a common complication of chronic respiratory disease, in particular COPD and diffuse interstitial lung diseases (DILD). PH in COPD is usually mild or moderate in intensity, although it frequently increases during sleep, effort and exacerbations. These repeated elevations in pulmonary pressure can lead to the development of right heart failure.57 Therefore, the presence of PH would suggest the need to evaluate the cardiopulmonary functional reserve by carrying out an exercise stress test. In DILD, PH is a factor for poor prognosis. In the case of primary pulmonary hypertension (PPH), fitness for work is determined by the symptoms and prognosis. Exercise intolerance is the main symptom in PH; exercise tolerance is independent of ventilatory function and is determined by the inability of the right ventricle to increase cardiac output in response to the metabolic demand.58

A very diverse group of diseases, both in terms of etiology and therapeutic possibilities and prognosis, is classified under the title of DILD. To reach the desired definitive diagnosis, clinical, radiological and histological data need to be brought together.60 In most DILD, exercise limitation is a principal symptom right from the early stages. From a functional point of view, they are characterized by the presence of a restrictive pattern with reduction in TLC and FVC with a normal FEV1/FVC ratio. There is also altered gas exchange with reduced DLCO; this is the most sensitive parameter in the early stages of the disease and is useful for monitoring progression.61 In idiopathic interstitial pulmonary fibrosis, it also has a prognostic value: a DLCO less than 40% at the time of diagnosis implies advanced disease and when DLCO values are less than 39% and 35%, life expectancy is 2 years and 1 year, respectively. Changes in FVC have been shown to be the best parameter for establishing disease prognosis. A drop in FVC of 10% in a period of 6 months implies greater mortality. The full assessment includes a standardized stress test, such as the 6-min walk test. A fall in oxygen saturation during or after the test or a distance walked of less than 250 meters at the time of diagnosis are factors with a poor prognosis.62 The exercise stress test with evaluation of VO2max does not provide further information for the evaluation and prognosis of the disease. In the follow-up of the disease, the 6-min walk test along with the FVC provides relevant information and has prognostic value.63 In patients with DILD who undergo lung transplant, the same monitoring that the patient had previously (if any) will continue during the six months post-transplant. After this period, the fitness for work will be reassessed. In this case, in addition to residual respiratory capacity, it must be taken into account that immunosuppressive medication is an increased risk factor in certain lines of work.

The recommended diagnostic procedures and the severity scale are described in Table 6.

The therapeutic regimens indicated must be taken into consideration for the evaluation of PI. The need for some types of treatment generally implies a serious clinical situation or involves some limitations derived from the side effects or limitations in the patient's mobility.

Home respiratory therapies [long-term home oxygen therapy (LTOT) and home mechanical ventilation (HMV)] meet both criteria: limitations in mobility and severity.

Respiratory failure and the need for LTOT generally indicate severe clinical deterioration and are usually regarded as a cause for PI. Limitations on mobility outside the home for patients on LTOT programs have been improved by the possibility of obtaining liquid O2 backpacks and portable concentrators. Depending on their causative disease, type of job and personal constraints, some patients can continue their active working life while receiving oxygen therapy.

Inhaling certain substances in the working environment can cause almost all the types of respiratory disease which in these cases would be called occupational disease. (Table 7). Its onset is independent of age and on many occasions, its identification may mean a difficult social and employment situation. In general, once the disease has been diagnosed, work-related exposure must be discontinued, either to avoid progression or as a consequence of the resulting functional limitations. Accordingly, in most cases, it creates an inability to carry out the usual work. The benefits accorded to a case of PI due to occupational disease are greater than those derived from PI due to common disease. It is more complex to evaluate than common disease. As in the latter, a definitive diagnosis and functional assessment are required, but it is also necessary to identify a causal relationship between a specific work-related agent and the development of the disease. Difficulty in establishing this relationship in a robust manner varies between the various diseases and is the key to diagnosis.

Diagnosis can be easy, as in the case of acute diseases caused by accidental inhalation. In other cases where an immunological mechanism is involved, such as occupational asthma or hypersensitivity pneumonitis, the reference test is a bronchial challenge test, but this is not always essential for reaching a definitive diagnosis.64 Pneumoconiosis or mesothelioma have some distinctive clinical characteristics that together with the history of work-related exposure, allow a high degree of certainty in determining the causal relationship.65 The major difficulties arise in diseases without specific characteristics of work-related exposure which could have other etiologies, as is the case in lung cancer, interstitial pulmonary fibrosis and COPD. Knowledge of the subject's work history is the first step required for assessment and more complex cases may need to be studied in specialized units.

The General Social Security Act defines occupational disease as “disease contracted as a result of work performed in the activities specified in the table and approved by the applicable provisions and development of this law, and caused by the action of elements or substances that are specified in the table for each occupational disease”.7 Royal Decree 1299/2006 approves the table of occupational diseases in the Social Security system and established criteria for their reporting and registration.66