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 ( ) Incidence of CTS.02 ( ) RR of CTS with abnl test 4 (3-5) Cost of screening $400 ($ ) Annual turnover rate.15 (.05 – 0.5) Cost per case of CTS $20,000 ($6000 – 70,000)

Markov Decision Model

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