"Methods Union administrative records identified 20,642 union carpenters who worked in Washington State from 1989 to 2003. The Department of Labor and Industries provided records of workers' compensation claims and associated medical care. Work-related back claims (n = 4,241) were identified by ANSI codes (back, trunk, or neck/back) or ICD-9 codes relevant to medical care consistent with a back injury. Cases (n = 738) were defined as back injury claims with >90 days of paid lost time; controls (n = 699) resulted in return to work within 30 days. Logistic regression models estimated odds ratios and 95% confidence intervals (OR, 95% CI) of delayed return to work (DRTW). Results Thirty percent of case claims and 8% of control claims were identified by an ICD-9 code. DRTW after back injury was associated with being female (2.7, 95% CI: 1.3-5.5), age 30-44 (1.2, 95% CI: 0.9-1.7) and age over 45 (1.6, 95% CI: 1.1-2.3), four or more years union experience (1.4, 95% CI: 1.1-1.8), previous paid time loss back claim (1.8, 95% CI: 1.3-2.5), and 30-day delay to medical care (3.6, 95% CI: 2.1, 6.1). Evidence of more acute trauma was also associated with DRTW. Conclusions Use of ICD-9 codes identified claims with multiple injuries that would otherwise not be captured by ANSI codes alone. Though carpenters of younger age and inexperience were at increased risk for a paid lost time back injury claim, older carpenters and more experienced workers, once injured, were more likely to have DRTW as were those who experienced acute events."

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