Table 1.
The proportion of fresh samples from different sources with pH ≤5.5 and the diagnostic accuracy of using this cut-off to detect gastric source overall, and in the presence or absence of prior antacid medication and confounding factors
| Sample | All | Antacid medication | No antacid medication |
All confounding factors* |
| Number with pH ≤5.5/total n (%) | ||||
| Gastric | 65/96 (68) | 30/42 (71) | 35/54 (65) | 32/44 (73) |
| Oesophageal | 59/90 (66) | 26/41 (63) | 33/49 (67) | 26/42 (62) |
| Saliva | 2/101 (2) | 2/40 (5) | 0/61 (0) | 2/43 (5) |
| Bronchial | 0/103 (0) | 0/41 (0) | 0/62 (0) | 0/45 (0) |
| Diagnostic test | Gastric pH versus all other samples (95% CI) | |||
| Sensitivity % | 68 (57, 77) | 71 (55, 84) | 65 (51, 77) | 73 (57, 85) |
| Specificity % | 79 (74, 84) | 77 (69, 84) | 81 (74, 86) | 79 (70, 85) |
| PPV % | 52 (45, 58) | 52 (42, 61) | 52 (43, 61) | 53 (44, 62) |
| NPV % | 88 (85, 91) | 89 (83, 93) | 88 (84, 91) | 90 (83, 92) |
| PLR | 3.3 (2.5, 4.2) | 3.1 (2.1, 4.5) | 3.4 (2.3, 4.9) | 4.0 (2.4, 5.7) |
| NLR | 0.4 (0.3, 0.6) | 0.4 (0.2, 0.6) | 0.4 (0.3, 0.6) | 0.4 (0.3, 0.6) |
| Overall accuracy† % | 76 (72, 81) | 76 (68, 82) | 77 (68, 82) | 77 (70, 83) |
*Confounding included antacid medication, pernicious anaemia or gastric surgery.
†Refers to the probability that the aspirate will be correctly identified.
NLR, negative likelihood ratio; NPV, negative predictive value; PLR, positive likelihood ratio; PPV, positive predictive value.