Table 2.

Breath carbon monoxide (CO) performance with self-report and liquid chromatography-tandem mass spectrometry (LCMSMS) urine and saliva cotinine as reference measures.

Reference measure	Cut-off (ng/ml)	Breath CO cut-off (p.p.m.)	Sensitivity (%)	Specificity (%)
Self-report	NA	≥2	98.9	32.9
		≥3	97.8	72.0
		≥4	96.7	89.0
		≥5	94.4	97.6
		≥6	92.2	97.6
		≥7	88.9	98.8
		≥8	86.7	100.0
		≥9	85.6	100.0
		≥10	81.1	100.0
		≥11	73.3	100.0
LCMSMS urine cotinine	≥0.2	≥2	85.6	26.9
		≥3	71.9	76.9
		≥4	64.4	90.3
		≥5	58.9	96.2
		≥6	57.5	96.2
		≥7	54.8	96.2
		≥8	53.4	100.0
		≥9	52.7	100.0
		≥10	50.0	100.0
		≥11	45.2	100.0
LCMSMS urine cotinine	≥25	≥2	100.0	35.4
		≥3	96.8	73.4
		≥4	95.7	91.1
		≥5	92.5	98.7
		≥6	90.3	98.7
		≥7	86.0	98.7
		≥8	83.9	100.0
		≥9	82.8	100.0
		≥10	78.5	100.0
		≥11	71.0	100.0
LCMSMS urine cotinine	≥100	≥2	100.0	34.1
		≥3	97.8	72.0
		≥4	96.7	89.0
		≥5	94.4	97.6
		≥6	92.2	97.6
		≥7	88.9	98.8
		≥8	86.7	100.0
		≥9	85.6	100.0
		≥10	81.1	100.0
		≥11	73.3	100.0
LCMSMS saliva cotinine	≥0.2	≥2	99.1	41.5
		≥3	91.6	80.0
		≥4	84.1	90.8
		≥5	79.4	96.9
		≥6	77.6	96.9
		≥7	73.8	96.9
		≥8	72.0	98.5
		≥9	71.0	98.5
		≥10	67.3	98.5
		≥11	60.7	98.5
LCMSMS saliva cotinine	≥10	≥2	100.0	33.7
		≥3	98.9	72.3
		≥4	97.8	89.2
		≥5	94.4	96.4
		≥6	92.1	96.4
		≥7	88.8	97.6
		≥8	86.5	98.8
		≥9	85.4	98.8
		≥10	80.9	98.8
		≥11	73.0	98.8

Sensitivity and specificity at cut-offs ≥2–11 parts per million (p.p.m.). NA: not applicable.