Table 2. Scan data for ADM plus the tandem FAST cytometer and REIS for HT29-spiked peripheral blood.

Sample	Sample size, no. of WBCs	REIS OTCs, no. of cells	Tandem OTCs, no. of cells	Tandem false negatives, no. of cells	Tandem sensitivity, %	Tandem false positives, no. of objects	Tandem specificity
1	6 × 106	76	65	11	86	13	2 × 10-6
2	3 × 106	102	101	1	99	5	1.7 × 10-6
3	4.5 × 106	200	196	4	98	19	4 × 10-6
Total	13.5 × 106	378	362	16	95	37	3 × 10-6

The sample is scanned first with the REIS to determine the total number of OTCs. The sample is then scanned with the FAST cytometer, which identifies the locations of possible OTCs, and then REIS scans only these locations. The tandem OTCs are those found in this operation. The false negatives are the cells missed by the tandem operation, and the sensitivity is the ratio of the OTCs detected by the tandem operation to total OTCs. The false positives are artifacts detected by the FAST cytometer that are indistinguishable from OTCs. The specificity is the ratio of false positives detected by the tandem operation to the total number of white blood cells (WBCs) in the sample.