Does pain severity predict stone characteristics or outcomes in emergency department patients with acute renal colic

Objectives After initial emergency department (ED) management of acute renal colic, recurrent or ongoing severe pain is the usual pathway to ED revisits, hospitalizations and rescue interventions. If index visit pain severity is associated with stone size or with subsequent failure of conservative management, then it might be useful in identifying patients who would benefit from early definitive imaging or intervention. Our objectives were to determine whether pain severity correlates with stone size, and to evaluate its utility in predicting important outcomes. Methods We used administrative data and structured chart review to study all ED patients with CT proven renal colic at six hospitals in two cities over one-year. Triage nurses recorded arrival numeric rating scale (NRS) pain scores. We excluded patients with missing pain assessments and stratified eligible patients into severe (NRS 8-10) and less-severe pain groups. Stone parameters were abstracted from imaging reports, while hospitalizations and interventions were identified in hospital databases. We determined the classification accuracy of pain severity for stones >5mm and used multivariable regression to determine the association of pain severity with 60-day treatment failure, defined by hospitalization or rescue intervention. Results We studied 2206 patients, 68% male, with a mean age of 49 years. Severe pain was 52.0% sensitive and 45.3% specific for larger stones >5mm. After multivariable adjustment, we found a weak negative association (adjusted OR =0.96) between pain severity and stone width. For each unit of increasing pain, the odds of a larger stone fell by 4%. Index visit pain severity was not associated with the need for hospitalization or rescue intervention within 60-days. Conclusions Pain severity is not helpful in predicting stone size or renal colic outcomes. More severe pain does not indicate a larger stone or a worse prognosis.