Pulmonary Medicine

Disability Evaluation (Impairment evaluation)

What every physician needs to know:

The management of a chronic lung condition does not end with treatment alone. Patients need additional assistance and guidance on issues related to lung impairment, such as causation or attribution, apportionment, eligibility for various compensation systems, workplace modifications or removal from the workplace, and vocational and other forms of rehabilitation. Because of a general fear of the legal system, pervasive confusion about various compensation systems, the mistaken notion that those who seek impairment evaluation are usually malingerers, and lack of training in impairment evaluation, most physicians shy away from providing this service, often with disastrous socioeconomic and medical consequences for the patient.

The physician's role in what is commonly referred to as "disability evaluation" is more properly termed "impairment evaluation," since the goal is objective measurement of the extent of loss of physical or physiological function. On the other hand, the impact of the loss of function on a person's ability to perform day-to-day activities is called disability. Disability evaluation is usually performed by administrative and legal experts, while physicians provide additional input on impairment. The two terms, impairment and disability, are not synonymous. Impairment may occur without disability, and disability may occur without measurable impairment. Furthermore, two individuals with exactly the same impairment may suffer differing impacts on their lives resulting in different levels of disability.

The Language of Impairment and Disability:

Specific terminology is used in conducting evaluations of impairment and disability:

Temporary vs. Permanent Impairment

Permanent impairment is not expected to improve with time and treatment. Temporary impairment is expected to do so.

Partial vs. Total Disability

Total disability implies that an individual is unable to perform any work of the kind that he or she has the skills and qualifications to perform. Partial disability implies that an individual is able to perform some, but not all, of the work.


Causation or attribution refers to whether an exposure has been a substantial contributing factor in either causing or exacerbating the lung disease. The level of certainty required in determining causation for occupational lung disease is different from the usual standard of 95% certainty used in medical research. The commonly accepted standard of certainty for occupational cases is that the illness is substantially caused by or exacerbated by an occupational exposure on a "more probable than not" basis, or a level of certainty greater than 50%.


Apportionment describes the relative contribution of multiple factors to the total lung impairment or disability. For instance, both chronic inhalational asbestos exposure and cigarette smoking may be contributory factors to lung cancer. From a scientific perspective, it is usually difficult, if not impossible, to "apportion" the relative roles of factors in causation of a complex, multifactorial disease. Physicians are often asked to state their opinion on apportionment in the context of the body of available knowledge in that area.

Are you sure your patient is eligible for an impairment rating? What should you expect to find?

The first step in evaluating impairment is confirmation of the diagnosis of lung disease. Because of the medicolegal nature of the evaluation, the physician should have a greater certainty of the medical diagnosis than is sometimes used in clinical practice. In other words, objective confirmation of the diagnosis is preferable.

The second step in evaluating impairment is defining maximal medical improvement (MMI). MMI occurs at the point at which no further clinical or physiological improvement is expected to occur following maximal therapy. If therapy has not been maximized, the physician should delay impairment evaluation. A permanent impairment evaluation should be performed at or after MMI has been reached.

Beware: There are many guidelines for rating impairment.

Several compensation systems exist, each with its own guidelines. Therefore, identification of the compensation system for which the patient is eligible is essential, and the evaluating physician must be familiar with the specific guidelines used for determining compensation. The most common compensation systems used in the US are the federally funded Social Security Impairment (SSI) system, the Veterans Administration system, and the Workers Compensation system.

While the rules for the last of the three vary from state to state, they usually follow one of the editions of the American Medical Association (AMA) Guides to the Evaluation of Permanent Impairment. The various editions of the AMA Guides to the Evaluation of Permanent Impairment have markedly different sets of recommendations on impairment evaluation, so one must choose the right edition for the purpose. Use of the wrong edition may result in an erroneous impairment rating.

While some guidelines are available on the Internet without charge, use of web-based AMA Guides to the Evaluation of Permanent Impairment carries a fee.

Although the American Thoracic Society (ATS) has also developed consensus guidelines for rating pulmonary impairment, these guidelines may not be accepted by a specific compensation program.

Social Security Impairment System

The SSI program has some unusual features that distinguish it from other compensation programs. First, the program requires a "hard copy" of the volume-time curve of a recent spirogram obtained following administration of inhaled bronchodilator (if obstruction is present), as well as a maximal voluntary ventilation (MVV) maneuver, a maneuver that is no longer routinely performed during pulmonary function testing. Second, the program incorporates arbitrary, height-specific cutpoints for spirometric lung function for deciding impairment status; the cutpoints are not determined by race, ethnicity, age, or gender.

Third, the program denotes the patient as impaired or not impaired, rather than specifying a percent impairment. In the setting of impaired/not impaired categorization, those considered impaired under Social Security criteria are expected to have an impairment sufficient to prevent working for a period of one year or longer. Finally, the program does not focus on occupational causation but on the disease itself; it also takes into account impairment from coexisting non-pulmonary conditions, such as substance abuse.

Workers’ Compensation System

Workers' compensation is a "no-fault" system of medical care and disability insurance in which private insurers (or self-insured employers) pay benefits to an employee who sustains an injury or illness because of a workplace exposure. Under workers' compensation laws, the workers cannot sue their employer for injury or illness.

Workers' compensation laws vary from state to state. While rules vary among states, they usually follow one of the various editions of the AMA Guides to the Evaluation of Permanent Impairment.

Choosing a Guideline

Patients who apply for disability can be classified into three general types:

  • Those with advanced lung disease who apply for disability benefits under the Social Security Impairment program.

  • Those with work-related lung disease who apply under the Workers’ Compensation System (but also other programs, such as the Black Lung Benefits Act for Coal Miners and Energy Employees Occupational Illness Compensation Program for Department of Energy Workers).

  • Those who develop lung disease while working for certain employers, such as the Veterans Administration.

Of course, some patients may fit into more than one category and may apply for more than one program contemporaneously. The physician should identify the most appropriate program(s) and be familiar with the guidelines.

General approach for evaluating pulmonary impairment

After determining patient eligibility for a specific compensation system (as described above), the physician gathers data that is relevant to rating pulmonary impairment. In general, impairment criteria are based upon the history, physical examination, and pulmonary function test results.

  • Relevant features in the history include occupational history, tobacco use, environmental exposures, and the presence of dyspnea, cough, sputum production, and wheezing.

  • Physical examination should include a description of breathing pattern, cyanosis, clubbing, adventitious lung sounds, and evidence of cor pulmonale.

  • Pulmonary function tests are the cornerstone for rating pulmonary impairment. Relationships between resting spirometric measurements (FVC and FEV1) and diffusing capacity measurements (DLCO) on one hand, and exercise-related maximal oxygen consumption (VO2max) on the other hand, have been established. On the basis of these studies, spirometry and diffusing capacity are the key objective elements in assessing respiratory impairment.

  • CXR or CT, cardiopulmonary exercise testing, and arterial blood gas determinations are usually not necessary for rating impairment. The role of cardiopulmonary exercise test in rating impairment is discussed below.

  • The sixth edition of the AMA Guides to the Evaluation of Permanent Impairment uses a standardized grid that incorporates five classes of impairment severity. The grids incorporate objective, test-based key criteria for defining the impairment class, along with other criteria for fine-tuning the severity grade within a given class. Among the objective tests (spirometry, DLCO, and cardiopulmonary exercise testing), the most severely affected test result is used to define the impairment class. Simpler grids are also used in other compensation systems.

What laboratory studies are useful in rating pulmonary impairment?

Laboratory studies are used primarily for confirming the diagnosis of lung disease, rather than for rating pulmonary impairment.

Immunological tests are useful in diagnosing occupational lung diseases (e.g., antibody tests for evaluating occupational asthma and hypersensitivity pneumonitis, and beryllium lymphocyte proliferation tests of blood or bronchoalveolar lavage fluid for assessing chronic beryllium disease).

For the purpose of rating impairment, resting and exercise-related hypoxemia derived from arterial blood gas results, adjusted for altitude and arterial PCO2 level, may be used under the SSI system to classify gas exchange abnormalities. Although the presence of hypoxemia noted on two occasions was previously used to rate impairment as severe under the fifth edition of the AMA Guides to the Evaluation of Permanent Impairment, the sixth edition does not include hypoxemia in the rating of pulmonary impairment. Hence, arterial blood gas analysis is unnecessary in impairment evaluation. The possible rationale for its exclusion in the AMA Guides sixth edition is that no validated relationship has been defined between resting arterial oxygenation and physiologic impairment. Presence of low PaO2 levels, however, continue to be useful in rating impairment under the Black Lung Benefits Act and Energy Employees Occupational Illness Compensation Program Act.

What imaging studies are useful in rating pulmonary impairment?

Imaging studies are primarily useful for confirming the diagnosis of lung disease. They are less useful in rating pulmonary impairment since the correlation between radiographic abnormality and physiologic dysfunction is imperfect.

CXRs and high-resolution CT of the chest are useful in diagnosing interstitial lung disease, small airways disease, lung neoplasms, and pneumoconiosis.

Chest radiographic evidence of pneumoconiosis is rated according to the International Labor Organization (ILO) classification scheme (also called "B-reading"), formulated under the Black Lung Act for coal worker's pneumoconiosis. The extent or profusion of small-sized opacities is rated as 0, 1, 2, or 3. An intermediate score of 1/0 (i.e., profusion of small opacities greater than 0 but less than 1) is often used to confirm the presence of pneumoconiosis in many compensation programs in the US.

What physiologic studies are useful in rating pulmonary impairment?

Physiologic studies are the foundation for rating pulmonary impairment. Several tests are useful in rating pulmonary impairment, including resting pulmonary function tests, methacholine bronchoprovocation, and maximal cardiopulmonary exercise testing. Performance of these tests should adhere strictly to the standards of the ATS.

Role of resting pulmonary function tests in rating impairment

The tests most commonly used in rating impairment are spirometry and measurement of diffusing capacity (DLCO). Relationships between resting spirometric and diffusing capacity measurements on one hand, and exercise-related maximal oxygen consumption on the other, have been established. On the basis of these studies, spirometry and diffusing capacity are the key objective elements in assessing respiratory impairment.

Role of spirometry in rating impairment

In obstructive airway disease, spirometry should be done following administration of an inhaled bronchodilator.

While not necessary for SSI rating, adjustment of pulmonary function tests for race and ethnicity is performed as part of other impairment assessments. According to the sixth edition of the AMA Guides to the Evaluation of Permanent Impairment, race- and ethnicity-specific NHANES III reference standards for spirometry should be used for Caucasian Americans, Mexican Americans, and African Americans. For the remainder of the population subgroups, no clear guidelines are provided.

Pulmonary function test criteria used under the SSI system are specific only to height and not adjusted for age, gender, race, or ethnicity. Therefore, under this system, older women are more likely to be rated as disabled than younger men. Furthermore, maximal voluntary ventilation, a test not usually performed, is required for the SSI rating for COPD.

Role of diffusing capacity in rating impairment

The corrected single-breath diffusing capacity is used under the AMA and Social Security guidelines for impairment rating, but it is not used under the Veterans Administration guidelines. Crapo's reference standards for DLCO are used for comparison.

Role of methacholine bronchoprovocation in rating impairment

Methacholine bronchoprovocation tests are useful for rating impairment for asthma. The methacholine PC20 (provocative concentration of methacholine in mg/mL that results in at least 20% drop in FEV1 compared to the pre-test baseline during a bronchoprovocation test) is a key parameter for rating asthma impairment under the sixth edition of the AMA Guides to the Evaluation of Permanent Impairment. The value for PC20 is usually increased among asthmatics who have been treated with maximal therapy. As a result, a normal value for PC20 on maximal asthma therapy may result in a 0% impairment rating for a well-controlled asthmatic.

Role of exercise test in rating impairment

Exercise tests are difficult to perform, expensive, and not readily available. Clear agreement on the role of exercise tests in the evaluation of pulmonary impairment is lacking. Generally, in cases in which dyspnea (a subjective sensation) is disproportionate to the resting pulmonary function test results, or when pulmonary function tests are difficult to interpret because of submaximal performance, cardiopulmonary exercise tests may be considered. Such tests may also help identify unanticipated coexisting conditions, such as cardiovascular or muscular disease, as the cause of exercise limitation.

When an individual's aerobic capacity is uncertain, maximal cardiopulmonary exercise testing may be useful in determining whether he or she can perform a job with a known energy requirement. Under the ATS guidelines, the estimation of impairment from maximal oxygen consumption (VO2max) is based on the premise that a worker can comfortably perform at 40% of VO2max for prolonged periods, and that VO2 requirements can be assigned to specific occupations. Those whose VO2max is less than 15 mL/kg/minute would be uncomfortable performing most jobs. Unfortunately, the data on the VO2 requirements of most jobs in modern workplaces are not currently available. Furthermore, jobs with the same title may vary considerably in their VO2 requirements from one work site to another.

Under the SSI system, submaximal exercise tests at a workload of approximately 17 mL O2 /kg/minute or less of exercise can be performed to obtain steady-state arterial blood gases, which are then used to evaluate impairment of gas exchange when criteria for both obstructive and restrictive disorders are not met.

How does one rate impairment for asthma?

Impairment rating for episodic diseases like asthma is problematic, and the ratings vary widely among various compensation systems. The methacholine PC20 is a key parameter for rating asthma impairment under the sixth edition of the AMA Guides to the Evaluation of Permanent Impairment. Under the SSI criteria, asthmatic patients may be rated by FEV1 or MVV or by a clinical history of frequent, severe exacerbations despite maximal asthma therapy.

Impairment ratings for occupational asthma is even more problematic than those for non-occupational asthma. In these cases, the impairment evaluation is performed using the scaling systems devised for non-occupational asthma at least two years after removing the individual from exposure. In many with occupational asthma, physiologic tests may be normal, and symptoms may be lacking in the absence of exposure to the specific agent. Therefore, it is difficult to evaluate impairment in such patients under the existing guidelines. Nevertheless, the best prognosis in immune-mediated (or sensitizer-induced) occupational asthma is attained by removing the individual from further exposure.

How does one rate impairment for pneumoconioses?

According to the AMA Guides to the Evaluation of Permanent Impairment, those who develop pneumoconiosis should limit further exposure to the offending agent, “particularly if radiographic changes have occurred at a relatively young age or if there is associated physiologic impairment.” It follows that an older patient who is nearing retirement, with minimal radiographic change after a long history of exposure, could elect to continue in the workplace under the assumption of a lower risk of developing future disabling disease. Such discretionary decisions should be made with informed discussions between the patient and physician.

The Veterans Administration system has specific guidelines for impairment ratings for pneumoconiosis.

Under the SSI system, common criteria for assessing lung diseases in general are used for rating impairment due to a pneumoconiosis. Black Lung Benefits Act for Coal Miners and Energy Employees Occupational Illness Compensation Program for Department of Energy Workers have specific guidelines for determining respiratory impairment that are available online.

How does one rate impairment for lung cancer?

According to the AMA Guides to the Evaluation of Permanent Impairment, lung cancer is a cause of severe impairment at the time of diagnosis. If no evidence of tumor is found at re-evaluation a year later, then impairment is recalculated on the basis of the degree of physiologic impairment present at that time. On the other hand, if there is evidence of tumor, the patient remains classified as severely impaired.

Under the SSI system, lung cancer produces impairment if it is unresectable, if it is incompletely resected, if it is recurrent or metastatic, if it has small cell histology, if it is a squamous cell cancer with metastasis beyond hilar nodes, or if it is one of other histologic types with metastasis to hilar nodes.

Under the Veterans Administration system, degree of impairment is not categorized clearly but is left to the judgment of the physician.

How does one rate impairment for sleep apnea?

Impairment ratings for sleep apnea are problematic, and they vary among compensation systems.

The variables used for pulmonary impairment rating (discussed above) cannot be used for rating impairment related to sleep apnea. Therefore, the AMA Guides to the Evaluation of Permanent Impairment recommend assessment of complications of sleep apnea (such as the presence of cor pulmonale or polycythemia). Any "add-on" for strictly pulmonary impairment must be determined by a sleep specialist and should not exceed 3% of total impairment.

Under the SSI system, sleep apnea is rated according to criteria for cor pulmonale, obesity, or organic mental disorders.

The Veterans Administration makes no mention of a specific impairment rating for sleep apnea.

What should the physician's report state?

Physicians' evaluations of impairment require a comprehensive report of the patient's history, physical examination, and review of objective tests. The assessment should provide clear and accurate answers, in lay terms, to the questions asked. The evaluation should state the diagnosis and whether MMI has been reached and should make note of the presence and degree of pulmonary impairment. The specific impairment scheme used (including the specific page and table of the guideline used) should be referenced. In work-related respiratory disorders, causation, apportionment, and work restrictions should also be addressed, as requested.

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