Development of a Severity Classification System for Sickle Cell Disease

Abstract

Purpose: There is no well-accepted classification system of overall sickle cell disease (SCD) severity. We sought to develop a system that could be tested as a clinical outcome predictor.

Patients and methods: Using validated methodology (RAND/UCLA modified Delphi panel), 10 multi-disciplinary expert clinicians collaboratively developed 180 simplified patient histories and rated each on multiple axes (estimated clinician follow-up frequency, risk of complications or death, quality of life, overall disease severity). Using ratings on overall disease severity, we developed a 3-level severity classification system ranging from Class I (least severe) to Class III (most severe).

Results: The system defines patients as Class I who are 8-40 years with no end organ damage, no chronic pain, and ≤4 unscheduled acute care visits due to vaso-occlusive crises (VOC) in the last year. Patients <8 or >40 years with no end organ damage, no chronic pain, and <2 unscheduled acute care visits are also considered Class I. Patients any age with ≥5 unscheduled acute care visits and/or with severe damage to bone, retina, heart, lung, kidney, or brain are classified as Class III (except patients ≥25 years with severe retinopathy, no chronic pain, and 0-1 unscheduled acute care visits, who are considered Class II). Patients not meeting these Class I or III definitions are classified as Class II.

Conclusion: This system consolidates patient characteristics into homogenous groups with respect to disease state to support clinical decision-making. The system is consistent with existing literature that increased unscheduled acute care visits and organ damage translate into clinically significant patient morbidity. Studies to further validate this system are planned.

Keywords: chronic pain; disease severity; expert panel; organ damage; vaso-occlusive crises.

Figure 1

Example rating form of patient scenarios. Each cell represents 1 patient scenario. The table is read from top to bottom and left to right. For example, the first cell in column A1 reads: “In a patient with no end organ damage, no chronic pain, 0–1 unscheduled acute care visits due to VOCs in the last year, with HbSS or HbSβ⁰, how often should this patient be seen by a SCD provider?” ^aThis table was replicated for each patient age group: Patient <8, 8–15 years old, 25–40 years old, >40 years old. Young children might have no history, so the classification system might not be as applicable. ^bA SCD provider includes any clinician treating SCD and its primary consequences (eg, hematologist or pulmonologist). ^cAdditional serious complications include end organ damage, sepsis, or other. ^dRisk of complications or death in the next 5 years for patients ≥16 years old and next 10 years for patients <16 years old. ^eChronic pain defined as ongoing pain present on most days over the past 6 months. fAcute care includes unscheduled office visits, ED visits, day hospital visits, and hospitalizations; VOCs include pain, priapism, acute chest syndrome, splenic sequestration, and hepatic sequestration. ^gRefer to Table 1 for definitions of end organ damage provided.

Figure 2

Expert agreement on overall disease severity classifications. Each cell represents 1 patient scenario. Class levels are color coded: The lightest blue represents Class I (least severe disease) and the darkest blue represents Class III (most severe disease).

Figure 3

Patient classification flow chart. Class I represents least severe disease and Class III represents most severe disease. ^aPatients ≥25 years old presenting with severe retinopathy, no chronic pain, and <2 unscheduled acute care visits due to VOCs in the last year are Class II.