Modeling the Cost Benefit of Nerve Conduction Studies in Pre-Employment Screening for Carpal Tunnel Syndrome Bradley Evanoff, MD, MPH Steve Kymes, PhD Washington University School of Medicine, St. Louis, USA
Pre-employment screening programs • Pre-employment medical screening is used to prevent new workers from starting jobs that pose higher risks for them • Such programs are common in the USA, and screen for susceptibility to such conditions as low back injury, allergies to specific compounds, and ability to safely use a respirator • Existing screening programs are rarely based on data showing effectiveness
Pre-employment screening programs • Yield of such screening can easily be estimated (De Kort and van Dijk; OEM 1997) • Example: screening laboratory workers for atopy • To avoid one case of allergy to laboratory animals, 122 job applicants must be screened, and 17 rejected for employment • 12 of the 17 rejected applicants will have incorrect diagnosis of atopy • What is the case for CTS screening?
Carpal Tunnel Syndrome (CTS) • A common peripheral nerve disorder • Multi-factorial disease risks: work-related physical exposures and non-work related personal factors • Pre-employment nerve conduction screening is promoted as a strategy to reduce CTS incidence in “high risk” jobs • Practice is common in USA, despite social controversy and no evidence of effectiveness
One study to date • Only one study (Franzblau 2004) has measured effectiveness of pre-employment nerve conduction screening • Retrospective cohort study of 2150 workers at one manufacturing plant who received nerve screening, but were hired regardless of results • Detailed cost outcomes data on compensation claims, time loss, hiring costs for replacement workers
Results • CTS 3.3 times more common among those with abnormal nerve studies at baseline BUT: • Majority of cases (63%) of CTS occurred in workers with NORMAL baseline results • Majority of workers with abnormal baseline did NOT get CTS (<2 per 100 per year) • Cost of screening was greater than the cost of cases avoided
Screening Model for CTS • Only one study in one employer • We examined different scenarios when screening would or would not be effective • Decision tree and Markov model comparing screening of all prospective employees versus no screening • Workers with abnormal studies not hired • Model follows a dynamic cohort of workers for 5 years following initial hire
Model Parameters Prevalence of abnl test .15 (.05 - .25) Incidence of CTS .02 (.005 - .03) RR of CTS with abnl test 4 (3-5) Cost of screening $400 ($100-1000) Annual turnover rate .15 (.05 – 0.5) Cost per case of CTS $20,000 ($6000 – 70,000)
Base Model: CTS costs per worker position No screening = $480 , Screening = $776 Difference = $296 (favoring NO screening)
Monte Carlo simulation • 10,000 iterations of model, varying parameters throughout range • Screening favored in 30% of the iterations; no screening favored 70% • Strategy of no screening dominated when: • Turnover rate >12% • Cost of CTS < $66,000 • Cost of test > $45
Sensitivity Analysis • Screening favored by: • Increased Relative Risk of CTS among those with abnormal vs. normal nerve test • High prevalence of baseline abnormal test • High incidence of CTS • High cost per case of CTS • Low screening costs • Low turnover
Limitations • Models with different assumptions will arrive at different answers • May be additional, uncounted costs of CTS to employer • Model probably biased toward screening • Model is from perspective of employer, does not account for costs borne by others • Many workers inappropriately rejected for each case of CTS prevented (base model=43) • Does rejecting workers from one employer prevent CTS in the total workforce?
Conclusions • Pre-employment screening for CTS not cost-effective for majority of employers • May be cost-effective in some circumstances • Post-offer screening for CTS should be carefully evaluated for yield before implementation (!) • Decision analysis is probably useful for other questions in occupational health and safety