Evaluation of the effectiveness of pre-employment screening

As pre-employment screening and selection is a main function in the protection of susceptible applicants from developing an occupational disease, we need insight into the effectiveness of this intervention under different exposure conditions. The aim of our study was to demonstrate the feasibility and usefulness of three indicators to evaluate the effectiveness of pre-employment examinations.

We used a pre-employment medical evaluation table to gather the data needed for the indicators for effectiveness. The first indicator chosen is the predictive value of a positive test result (PPV) corresponding to the percentage of applicants who will develop an occupational disease after a positive test result. The second indicator is the number of pre-employment medical examinations needed to reduce the number of new cases of an occupational disease by one (number needed to test, NNT). The third is the number of rejections for the job, as the consequence of a positive test result, needed to reduce the number of new cases of an occupational disease by one (number needed to reject, NNR). To illustrate feasibility and usefulness, we used the example of potroom asthma in the primary-aluminium industry. We used data on personal risk factors and on the incidence of potroom asthma from a nested case-control study in the Netherlands.

The three indicators for effectiveness could be applied. For high incidence rates, defined as 0.04 (40 cases/1000 employees per year), the PPV values for personal risk indicators varied from 5% to 27%. The NNT varied from 116 to 667. Finally, the NNR varied from 4 to 20. For low incidence rates, defined as 0.005 (5 cases/1000 employees per year), the PPV values were low (0.6% to 5%). The NNT were high (1111 to 5000). The NNR varied from 23 to 155.

The three indicators for effectiveness are applicable under the condition of the availability of relevant empirical data. The indicators provided useful information for the evaluation of the effectiveness of specific tests, which might be added as selection criteria. The personal risk factors studied were far from effective as selection instruments, especially in situations where a low incidence of potroom asthma exists. Personal risk factors at the pre-employment stage should not be added to the standard procedure to select susceptible applicants. Under conditions, they may be taken into account in a workers' health surveillance programme. As a contribution to evidence-based occupational medicine, we recommend the use of the pre-employment medical evaluation table and the three chosen indicators for effectiveness as a standard tool to evaluate the effectiveness of pre-employment medical examinations.