Medical measurement concept · BEGINNER LESSON
Disease severity
Disease severity is a way to classify how serious a health condition is, from mild to severe, based on how much it affects daily life or expected health burden. In some systems it is assessed with qualitative categories; in others it is approximated with quantitative measures such as absolute or proportional QALY shortfall.
What it is
Disease severity is a label for how serious a health condition is. In the sources, severity can be described qualitatively as mild, moderate, severe, or very high, or it can be approximated with quantitative measures that compare a patient’s remaining health to that of a healthy person. One example is quality-adjusted life years (QALYs), a measure that combines length of life and health-related quality of life.
[1] Table 2. [3] Agreement in Qualitative and Quantitative Assessments of Disease ...
How it is defined and measured
One operational definition says mild illness is present but tolerable and does not affect activities of daily living, moderate illness cannot be ignored and does affect daily living, and severe illness is the worst possible health condition that could be imagined. Another approach uses absolute QALY shortfall (AS), which is the difference between a healthy person’s remaining quality-adjusted life expectancy and a patient’s remaining quality-adjusted life expectancy, and proportional QALY shortfall (PS), which is that difference divided by the healthy person’s value.
[1] Table 2. [3] Agreement in Qualitative and Quantitative Assessments of Disease ...
How severity is used in real-world data
For COVID-19, the U.S. Food and Drug Administration proposed categories such as asymptomatic, mild, moderate, severe, and critical. A validation study tested code-based algorithms in Medicare administrative data against medical records as the reference standard, using positive predictive value (PPV), which is the share of coded cases that were confirmed. Performance varied by category, and the authors noted that the operational definitions were only moderately effective for some severity levels.
Limitations
Disease severity is not measured the same way in every setting. Qualitative severity categories can vary across assessors, and quantitative shortfall measures do not fully capture all judgments used in reimbursement systems. In the COVID-19 validation study, performance differed across severity levels, showing that a coding algorithm may identify the disease itself more reliably than the exact severity category.
[2] Validation of the US Food and Drug Administration's COVID-19 Disease Severity Categorization for Use in Real-World Data - PubMed [3] Agreement in Qualitative and Quantitative Assessments of Disease ...
SEE THE IDEA
Ways disease severity is represented
How much the condition affects activities of daily living and day-to-day functioning.
A label such as mild, moderate, severe, or very high.
A comparison of remaining health with a healthy person using AS or PS.
Code-based algorithms try to assign severity from claims data.
Clinical impact can be translated into either qualitative categories or quantitative measures, and code-based systems attempt to infer those categories from records.
Disease severity can be judged directly from impact, or estimated from records and shortfall measures, but the match is imperfect.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.