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HSP subsets

7. Palpable purpura; age at disease onset ≤20

6. Palpable purpura; age at disease onset >20; biopsy showing granulocytes around small blood vessels

4. No palpable purpura; age ≤20 at disease onset; biopsy showing granulocytes around small blood vessels

3. No palpable purpura; age ≤20 at disease onset; negative biopsy, but GI bleeding

Non-HSP subsets

1. No palpable purpura; age >20 at disease onset

2. No palpable purpura; age ≤20 at disease onset; biopsy negative for granulocytes around small blood vessels; no GI
     bleeding

5. Palpable purpura; age >20 at disease onset; negative biopsy

* The subset numbers also appear below the subset boxes in Figure 1. The classification tree yields a sensitivity of 89.4% and a specificity of 88.1%. See Table 3 for definitions of criteria. GI = gastrointestinal.