Defining Severity of Illness
Severity of illness refers to the extent of physiologic instability or organ system loss of function a patient experiences during an episode of care. RHIA candidates should understand that severity of illness is distinct from complexity of care and from risk of mortality, even though these concepts are related and sometimes confused.
Common Severity Scoring Systems
Several clinical severity scoring tools are used across healthcare settings, including the Acute Physiology and Chronic Health Evaluation, commonly known as APACHE, used primarily in intensive care units to predict mortality risk based on physiologic variables collected shortly after admission. The Sequential Organ Failure Assessment score tracks the degree of organ dysfunction across multiple organ systems over the course of an ICU stay, allowing clinicians to monitor whether a patient's condition is improving or deteriorating.
Why Severity Matters for Coding and Documentation
- Accurate capture of severity-related diagnoses supports appropriate DRG and APR-DRG subclass assignment
- Severity documentation justifies the medical necessity of intensive interventions and extended length of stay
- Quality measures that report risk-adjusted outcomes rely on accurate severity data to fairly compare hospitals treating different patient populations
- Underdocumentation of severity can make a hospital appear to have worse outcomes than its actual case mix would predict, since risk adjustment cannot account for conditions that were never documented or coded
Clinical Documentation Improvement Focus Areas
Clinical documentation improvement specialists often focus queries on conditions that meaningfully affect severity classification, such as acute organ dysfunction, malnutrition, and specific types of respiratory failure, ensuring that physician documentation captures the clinical significance of these findings with sufficient specificity for coding.
Severity and Resource Utilization
Higher severity of illness generally correlates with greater resource utilization, including nursing intensity, diagnostic testing, and length of stay, which is why severity-adjusted classification systems like APR-DRG were developed to better align reimbursement with the actual clinical resources required to care for sicker patients.
Exam Tip
Be prepared to explain why accurate severity documentation is essential not just for reimbursement but for fair, risk-adjusted quality comparisons between healthcare organizations.