First calculate the pARC logit:

logit = -8.7 + 1.28*(male sex) + 0.38*(age 5-7.9 y) - 1.05*(male and age 5-7.9 y) - 0.72*((female and age 8-11.9 y) or (male and age 8-13.9 y)) + 0.47*(pain 24-<48 h) + 0.10*(pain 48-96 h) + 1.05*(pain with walking) + 0.46*(migration to RLQ) + 1.14*(maximal RLQ tenderness) + 0.67*(guarding) + 1.77*sqrt(ANC capped at 14)

Then convert logit to probability:

appendicitis risk (%) = 100 * exp(logit) / (1 + exp(logit))

Predicted risk	pARC band
<5%	Very low
5-14%	Low
15-24%	Intermediate-low
25-49%	Intermediate
50-74%	Intermediate-high
75-84%	High
≥85%	Very high

Pediatric Appendicitis Risk Calculator (pARC)