Sensitivity and specificity of the breath hydrogen test for lactose intolerance
| Sensitivity (%) | 0–3 hours | 3–6 hours | 6–9 hours | 9–12 hours |
|---|---|---|---|---|
| Total | 33.7 | 56.1 | 60.2 | 63.3 |
| CC/GG | 100 | 100 | 100 | 100 |
| CT/GA | 42 | 60 | 63 | 64 |
| TT/AA | 14 | 31 | 34 | 40 |
| Specificity (%) | ||||
|---|---|---|---|---|
| Definitive diagnosis of lactose intolerance was based on a substantial improvement in the number and severity of symptoms after 12 weeks of complete exclusion of lactose from the diet, including hidden lactose. A breath test was positive if the breath hydrogen rose 20 ppm over the nadir during the time interval defined after ingesting 50 g lactose (1 g/kg for children). Sensitivity (%) = (TP×100)/(TP+FN) where TP+FN = total number of patients diagnosed clinically with lactose intolerance. Specificity (%) = (TN×100)/(TN+FP) where TN+FP = total number of patients diagnosed clinically as not having lactose intolerance. True positive (TP) = positive breath test in a patient diagnosed with lactose intolerance. True negative (TN) = negative breath test in a patient without lactose intolerance. False positive (FP) = positive breath test in a patient without lactose intolerance. False negative (FN) = negative breath test in a patient diagnosed with lactose intolerance. It is also possible to then calculate the positive (PV+) and negative (PV−) predictive values. (PV+) % = (TP×100)/(TP+FP); (PV−) % = (TN×100)/(TN+FN). The optimum time was six hours with a PV+ for all patients of 95%, and a PV− of 34%. | ||||
| Total | 96 | 88 | 84 | 80 |
| CC/GG | 100 | 100 | 100 | 100 |
| CT/GA | 100 | 88 | 88 | 77 |
| TT/AA | 93 | 87 | 81 | 81 |