Asano-Gonnella Center for Research in Medical Education & Health Care

Disease Staging

Disease Staging was first developed to measure the problem-solving ability of medical students or physicians. It is now being used primarily to measure quality and cost of care.

Disease Staging is a classification system that uses diagnostic findings to produce clusters of patients based on etiology, pathophysiology and severity. It can serve as the basis for clustering clinically homogeneous patients to assess quality of care, analysis of clinical outcomes, utilization of resources, efficacy of alternative treatments and assignment of credentials for hospital privileges. Staging was also designed as a quality assurance tool for evaluating ambulatory care by comparing levels of severity at the time of hospitalization for patients receiving their health benefits from government and private insurers.

Coming full circle, Disease Staging has recently been used as an educational tool to document and monitor the clinical experiences of medical students in different clinical clerkships and in different clerkship sites to explore the mix off patient severity available for medical students’ learning and assessment. This link between medical education and health services research can help assure that medical school faculty will be reminded of the context of medical education in the broader healthcare arena.

For the past three decades, Disease Staging has been used in the US and internationally on a variety of projects and research studies.   The links below provide more information about Disease Staging and its applications.

Where? Why? How serious? These are the basic questions that a clinician must attempt to answer when a patient presents with a medical problem. The same questions must be answered to make appropriate comparisons in studies of outcomes, quality, or costs of care. The “where” is the specific organ or system of the body; the “why” is the etiology of the problem; and the “how serious” is the pathophysiologic changes that have occurred and the ranking of the disease’s complications.

Physicians use information from a patient’s history, physical examination, laboratory findings, and other diagnostic tests to answer these questions in order to diagnose a disease, to estimate the patient’s prognosis, and to prescribe appropriate treatment. Ideally, answers should be available before therapeutic intervention. Even in those cases when definitive answers may not be available and treatment must be given, it should be based on the presumptive answers to these questions.

Disease Staging is a classification system that uses diagnostic findings to produce clusters of patients who require similar treatment and have similar expected outcomes. It can serve as the basis for clustering of clinically homogeneous patients to assess quality of care, analyze clinical outcomes, review utilization of resources, assess efficacy of alternative treatments, and assign credentials for hospital privileges.

Ideally, a diagnostic label should have explicit data about the location of the health problem, the cause of the problem, and the severity of the problem. The majority of diagnostic labels identify the site of the disease (e.g., appendicitis, cholecystitis, diverticulitis, and peptic ulcer). Some provide information about the system involved and cause of the problem (e.g., pneumococcal pneumonia and urinary tract infection caused by E. coli). Other diagnostic labels are manifestations of problems (e.g., hypertension and anemia). A few, because of the body system involved, also convey a degree of severity (e.g., myocardial infarction or bacterial meningitis). And some may even be distinguished by the time of onset (e.g., congenital toxoplasmosis).

Only in the discipline of cancer has the medical profession developed a diagnostic classification that includes severity based on the understanding of the need to measure the efficacy of various treatments for similar clusters of patients. Now that society is challenging the medical profession to document quality of care in a more objective manner, similar measurement instruments are needed for all medical problems.

The Disease Staging criteria define levels of biological severity for specific medical diseases, where severity is defined as the risk of organ failure or death. The classification is based on the severity of the pathophysiologic manifestations of the disease:

Stage 1

A disease with no complications

Stage 2

The disease has local complications

Stage 3

The disease involved multiple sites, or has systemic complications

Stage 4


Subdivisions of these stage levels have been defined to allow more precise classification. The challenge is to include enough detail to allow for a rich description of each disease and yet not be so overwhelmingly complete that the staging is cumbersome.

In the definition of the Staging criteria, most of the diseases begin at Stage 1 and continue through Stage 4. There are several exceptions to this rule. Some self-limiting diseases, such as cataracts, do not include a Stage 3 or 4. Other criteria begin at either Stage 2 or 3 since they are often complications of other diseases e.g., bacterial meningitis, which can be a complication of sinusitis, otitis media or bacterial pneumonia). Stage 0 has also been included in the classification of diseases for patients with a history of a significant predisposing risk factor for the disease, but for whom there is currently no pathology (e.g., history of carcinoma or a newborn baby born to a mother suspected of having an infection at the time of delivery).

The Stage levels are ordinal in nature for each medical problem. Stage 1 of one disease may have different implications for resource use, treatment, and prognosis than a similar stage of another disease. For example, hyperglycemia (Stage 1, diabetes mellitus) is different than positive serological evidence of AIDS (Stage 1). Even when major pathophysiologic damage exists such as coma, which in all diseases is a Stage 3 complication, the prognosis may be different for each disease since for some there is treatment which may reverse the complication. Treatment, whether medical or surgical, has not, however, been introduced into the staging classification; staging is driven by the natural history of the disease. Nor has quality of life been taken into consideration in Disease Staging. Controlling for other factors (e.g. choice of treatment, age, and presence of co-morbid disease), risk of death is a function of etiology and state of disease. While this risk generally increases with each higher Stage level, it may vary dramatically by Stage from one disease to another.

It is important to distinguish the etiology of a disease whenever possible. For example, “pneumonia” does not specify etiology. Designating that the pneumonia was bacterial in origin would be an improvement, (e.g., “bacterial pneumonia”), but optimally a physician should document the specific bacteria causing the pneumonia (e.g., pneumococcal pneumonia).

Health problems, such as congestive heart failure, and laboratory findings, such as anemia, that may result from a variety of causes, are not diagnoses. When such problems are recorded as the only evidence and stated as the patient’s “diagnosis,” the implication is that the physician did not know, or did not document, the disease process that produced the problem. Unfortunately, many users of medical information fail to distinguish between non-specific health problems (e.g., symptoms and laboratory findings) and diagnoses of specific diseases. As a result, patients may be inappropriately classified for the purposes of reimbursement, for the analysis of resource utilization, and for the assessment of quality of care.

Some diseases may have multiple etiologies (e.g., bacterial pneumonia). While the Staging classification is essentially the same for pneumonia due to Pneumococcus as it is for that due to Staphylococcus or Pseudomonas, each type of bacterial pneumonia should be analyzed separately when evaluating quality of care, clinical trials, and utilization of resources because of the varying prognosis associated with each.

There are a number of complications (for example, sepsis and congestive heart failure) that may result from many diseases. Generally, these complications have been assigned the same integer state level across the different diseases, although not necessarily the same substage level. Different integer stage levels have been used when the complication may indicate different levels of severity depending upon the underlying disease. For example, pneumonia is classified as a Stage 2 complication when it occurs secondary to other problems. There are a few diseases, such as botulism, where aspiration pneumonia or bacterial pneumonia is a reflection of the systemic nature of the problem rather than just the involvement of the respiratory system. For these diseases, pneumonia is classified as a Stage 3 complication.

In addition to the stages of the disease, each criteria set includes a specification of “diagnostic findings” that can be used to validate the presence of the disease and stage level. The diagnostic findings include physical findings, radiological and laboratory results, and pathological and operative reports.

Applications of Disease Staging

Disease Staging may be used to document potential quality of care problems in ambulatory settings by providing data relating to patients’ severity of illness at the time of hospitalization. Patients admitted to the hospital with advanced stages of illness represent possible failures of outpatient care. For example, an admission for cellulitis secondary to diabetes mellitus might have been preventable if the disease progression could have been averted with appropriate outpatient care.

For some diseases, such as appendicitis, hospitalization is clearly appropriate at the earliest stage of the disease. Other diseases, such as essential hypertension, rarely require hospitalization at the early stages; hospitalization is only required if the disease progresses to more advanced stages.

Because admitting patients to an acute care hospital involves incurring significant cost and potential risk, patients should be admitted to the hospital only if the expected benefits outweigh the costs and risks of the admission. Questions to address include:

Is inpatient diagnostic testing required? Do the symptoms suggest a serious illness which, if confirmed, may require immediate treatment? Does the patient require treatment that is most appropriately provided as an inpatient? Does the patient require the types of monitoring and nursing care available only in an acute care hospital?

Classification of severity of illness at the time of hospitalization is important for analysis of both inpatient and outpatient care. Comparisons of inpatient care outcomes can be accomplished only if one adjusts for patent risk at time of admission.

For patients admitted at earlier stages of illness, one may question whether an acceptable level of care could have been provided in an outpatient setting. A number of factors could make such an earlier stage admission appropriate. For example, a patient with acute symptoms (e.g., chest pain), but without a confirmed diagnosis, may be appropriately admitted to the hospital until a diagnosis and a decision can be made as to whether further inpatient care is necessary. A patient may have other co-morbid conditions (for example, poorly controlled diabetes mellitus) that make the admission advisable, or a patient may choose to undergo an elective surgical procedure that must be performed as an inpatient. A patient with osteoarthritis of the hip who decides to have a total hip replacement would clearly require hospitalization.

For patients hospitalized at more advanced stages, the issue is whether the patient has complications that could have been preventable with earlier inpatient care. For example, a patient admitted with acute cholecystitis and gangrene of the gallbladder has a serious complication that may have been prevented with earlier hospitalization and treatment.

Timeliness of admission is, in part, a function of whether hospitalization is the first or subsequent admission for a particular complication of episode of care. For example, a first admission at advanced-stage cancer should raise questions about whether earlier detection was feasible. Subsequent scheduled admissions for the same patient to undergo chemotherapy would not, of course, raise the same question.

It is important to differentiate the concept of a timely admission from a preventable admission. For example, an admission at Stage 1 appendicitis is timely and, given current medical knowledge, not preventable. Such an admission does not raise issues of appropriateness of care. On the other hand, while an admission for Stage 2.5 diabetes mellitus and cellulitis is also timely, it may have been a preventable admission if the disease progression could have averted with appropriate outpatient care.

Disease Staging should be an integral part of systems designed to analyze resources utilization. Differences in length of stay and cost may result from differences in patient populations treated, as well as from differences in efficiency. Etiology and stage of disease are directly related to the use of resources and must be considered in these types of analyses, whether the focus is at the level of an individual physician, a hospital product line, or an entire institution.

In addition to the stage of the principal disease, other variables to be included in analysis of utilization include: presence of co-morbid, or co-existing, medical problems (e.g., presence of diabetes mellitus in a patient hospitalized for appendicitis – both the diabetes mellitus and appendicitis should be staged); reason for admission (e.g., for diagnostic purposes, therapeutic purposes, both diagnosis and therapy, chemotherapy, or observation); and the use of surgical procedure of special units (e.g., ICU, CCU), if such use is justified by the needs of the patient.

Use of resources depends on the clinical status of the patient, the reason for admission, and whether the latter is the first or one of many re-admissions. For instance, a woman with Stage 3 cancer of the breast will consume more resources during the first hospitalization, when more diagnostic and therapeutic interventions will be used than on her third hospitalization, when for the same problem she may likely receive only chemotherapy or radiation therapy. In addition, the social support needs of the patient should be considered, although this variable would have a greater impact on timing of hospitalization and length of stay than on the diagnostic or therapeutic intervention.

By using Disease Staging, variations in resource use resulting from patient differences can be controlled, thereby allowing the manager or researcher to appropriately focus on the analysis of differences resulting from variation in physician and institutional practices. For similar reasons, reimbursement systems should be modified to account for differences in severity of illness.

Whether the goal is assessment and improvement of the process of care or evaluation of clinical outcomes, there is a need for clinical specificity. The Centers for Medicare and Medicaid Services (CMS) and several statewide data organizations publish institution-specific, and in some cases physician-specific, information on outcome measures such as mortality. Without appropriate ways to account for differences in the severity of the patient mix treated, the relevance of these types of analyses is questionable. For example, analysis of data from the National Hospital Discharge Survey demonstrated a 5.6 % mortality rate for patients hospitalized with Stage 1 bacterial pneumonia, 9.5% for those with Stage 2, and a 33.1% mortality rate for Stage 3.29. These estimates were further refined by considering the specific etiology (organism) of the pneumonia.

As a part of a quality improvement program, these types of advanced-stage admissions should be reviewed to evaluate whether they resulted from physician-related problems (e.g., delayed or incorrect diagnosis or treatment), patient-related problems (e.g., failure to seek timely care or comply with prescribed treatment) system problems (e.g., lack of access to care), or were not preventable (e.g., resulting from rapid disease progression in a particular patient).

Disease Staging can also be used as a direct measure of patient outcomes by studying changes in disease stage over time. For instance, severity at hospital admission can be compared with severity at discharge. Patient-based longitudinal data can be used in conjunction with Disease Staging to assess changes in severity of illness for defined populations and specific episodes of care.

Another valuable use of Disease Staging is the evaluation of processes as well as outcomes of medical care. A great deal of activity is currently being devoted to the development of clinical guidelines designed to reduce uncertainty and help guide the process of care. One of the difficulties faced in guidelines development is that the appropriateness of a specific diagnostic test or prescribed treatment varies by stage of disease. By defining stage-specific criteria, it is possible to improve the specificity of clinical guidelines and process review criteria and to make them more useful and acceptable to clinicians.

The primary objective of clinical trials is to test the efficacy of therapeutic interventions under highly controlled conditions. By using Disease Staging to help specify the study population, comparability of the treatment and control groups can be assessed. Staging allows the investigator to stratify patients more accurately, both for their principal diagnosis or problems and for any co-morbid conditions that they may have. Depending on the goals of the trial, it can be restricted to samples defined using specific stages of disease or designed to allow the assessment of efficacy across different levels of severity.

Severity of illness, as documented by Disease Staging, may be used to evaluate the appropriateness of current or planned staffing levels within hospitals or managed care institutions in relationship to patients’ health care needs. Staging can provide severity-level data for specific patient groups that may justify establishing or expanding special care units or securing special diagnostic equipment or other facilities.

A major responsibility of medical specialty boards is the development and administration of procedures and examinations for board certification and recertification. Disease Staging has been used to classify the content of test items from the board certification/recertification examinations administered by the American Board of Family Practice and to analyze medical licensing examinations in Japan.  Each item on the examination is classified by organ system, etiology, and stage of illness, along with other dimensions such as age group affected and whether the item focuses on diagnosis or management.

Use of this type of classification enables the specialty board to assess the current mix of items and begin to develop a “blueprint” to guide development of future examinations. For example, by using Disease Staging, one can refine the assessment of the physician’s knowledge of diabetes mellitus management to assure that there is an appropriate mixture of items relevant to the early stages, as well as prevention and management of specific advanced stage complications.

Disease Staging can be used in the assignment of hospital clinical privileges.  Currently, the delineation of clinical privileges is primarily procedure-oriented, even in the medically-oriented specialties. For example, a general internist may be credentialed to perform procedures such as arterial puncture, thoracentesis, and lumbar puncture. However, the skills necessary to successfully perform an arterial puncture say very little about the physician’s ability to diagnose or manage the complex patient with advanced-stage medical problems.

Disease Staging can be used to delineate disease-specific privileges that more appropriately reflect the clinical challenges of patient management. For example, a board certified general internist may have the appropriate education and experience to manage early state diabetes mellitus, but not to manage a patient admitted for hyperosmolar coma. Potentially, the volume and outcomes of stage-specific experience could also be monitored, as is increasingly done for surgical volume and outcomes, to reassess the privileges assignment.

A significant part of both undergraduate and graduate medical education involves increasing levels of patient care responsibility as the experience of the student/physician increases. Disease Staging can be used as a part of systems designed to document these clinical experiences. For example, what is the mix of severity of illness of patients with diabetes mellitus seen by medical students? Does the student have adequate experience managing a patient with this disease to avoid, as well as in treating complications which may occur? Does this vary depending on the site where the students perform their clerkship? Is there significant variation from student to student?

Similarly, Disease Staging concepts can be used to evaluate the content of the curriculum. To what extent does the medical curriculum address Stage 1 illness and to what extent does it address Stage 3 illness? To what extent is attention devoted to problems associated with particular body organ systems or to problems of a particular etiological nature?

Use of Disease Staging can also help the student and resident become more effective diagnosticians. By understanding the evolution of a disease, the physician will use the laboratory more effectively and avoid delay in arriving at an accurate diagnosis.