An evaluation of the K2 asbestos screening test

The predictive ability of the K2 Asbestos Screening Test was determined by comparing the results obtained with the test and confirming analysis by polarizing light microscopy on 90 bulk insulation samples. The test yielded 38.9% true positives, 4.4% true negatives, 56.7% false positives and 0% false negatives. The proportion of false positives was significantly different from that reported by the researchers who developed the test and found that the test would not yield false positives. The results of this study are similar to those reported in a previous evaluation of the test. It was concluded that the screening test is not an effective screening tool because of the high proportion of false positives, as reflected by marginal values of specificity and positive predictive value. It was noted that problems with the test might result from failure of the wash steps to adequately remove positive interferences apparently associated with gypsum and mineral wool. Problems in interpreting color changes were noted also.