Table 3.
The diagnostic accuracy of the modified and standard pH stick tests for all gastric samples compared with non-gastric samples tested at the pH≤5.5, including the absence or presence antacid medication
| Diagnostic test | pH stick | All | Antacid medication | No antacid medication |
All confounding factors* |
| Gastric pH≤5.5 versus all other samples (95% CI) | |||||
| Sensitivity % | Standard | 68 (57 to 77) | 71 (55 to 84) | 65 (51 to 77) | 73 (57 to 85) |
| Modified | 66 (56 to 75) | 67 (51 to 80) | 65 (51 to 78) | 68 (52 to 81) | |
| Specificity % | Standard | 79 (74 to 84) | 77 (69 to 84) | 84 (74 to 86) | 79 (70 to 85) |
| Modified | 81 (76 to 85) | 81 (72 to 87) | 81 (70 to 87) | 82 (74 to 88) | |
| PPV % | Standard | 52 (45 to 58) | 52 (42 to 61) | 53 (44 to 62) | 53 (44 to 62) |
| Modified | 53 (46 to 59) | 55 (44 to 65) | 57 (46 to 67) | 57 (46 to 67) | |
| NPV % | Standard | 88 (85 to 91) | 89 (83 to 93) | 90 (84 to 93) | 90 (84 to 93) |
| Modified | 88 (84 to 90) | 87 (81 to 91) | 88 (83 to 92) | 88 (83 to 92) | |
| PLR | Standard | 3.3 (2.5 to 4.2) | 3.1 (2.1 to 4.5) | 4.0 (2.7 to 5.9) | 3.4 (2.3 to 4.9) |
| Modified | 3.4 (2.6 to 4.5) | 3.4 (2.2 to 5.2) | 3.4 (2.5 to 4.2) | 4.0 (2.4 to 5.7) | |
| NLR | Standard | 0.4 (0.3 to 0.5) | 0.4 (0.2 to 0.6) | 0.4 (0.3 to 0.6) | 0.4 (0.2 to 0.6) |
| Modified | 0.4 (0.3 to 0.6) | 0.4 (0.3 to 0.6) | 0.4 (0.3 to 0.6) | 0.4 (0.3 to 0.6) | |
| Overall agreement % |
Standard | 76 (72 to 81) | 76 (68 to 82) | 77 (71 to 82) | 77 (70 to 83) |
| Modified | 77 (73 to 81) | 77 (70 to 83) | 77 (71 to 83) | 78 (71 to 84) | |
*Confounding factors included antacid medication, pernicious anaemia and/or gastric surgery.
NLR, negative likelihood ratio; NPV, negative predictive value; PLR, positive likelihood ratio; PPV, positive predictive value.