Table 4.
Sensitivity analyses
| Hyponatraemic serum sodium value recorded in the LABKA research database (mmol/L) | Primary analysis (including all admissions for all patients in the study period), % (95% CI) | Sensitivity analyses |
||||
|---|---|---|---|---|---|---|
| Requiring at least one serum sodium measurement during hospitalisation, % (95% CI) | Requiring >1 serum sodium measurement during hospitalisation, % (95% CI) | ICD-10 algorithm restricted to code E87.1A and P74.2B, % (95% CI) | Restricting to first admission per patient in the study period, % (95% CI) | |||
| Overall | ||||||
| Na<135 | Sensitivity | 1.8 (1.7 to 1.8) | 1.8 (1.7 to 1.8) | 1.9 (1.8 to 2.0) | 0.7 (0.6 to 0.7) | 1.7 (1.7 to 1.9) |
| Specificity | 100 (100 to 100) | 100 (100 to 100) | 100 (100 to 100) | 100 (100 to 100) | 100 (100 to 100) | |
| PPV | 92.5 (91.8 to 93.1) | 95.4 (94.8 to 95.9) | 95.8 (95.2 to 96.3) | 94.6 (93.6 to 95.6) | 93.5 (92.0 to 94.7) | |
| NPV | 86.2 (86.2 to 86.2) | 76.9 (76.8 to 77.0) | 74.7 (74.6 to 74.8) | 86.1 (86.0 to 86.1) | 91.6 (91.6 to 91.7) | |
| Cut-off points for increasing severity of hyponatraemia | ||||||
| Na<130 | Sensitivity | 5.3 (5.2 to 5.5) | 5.3 (5.2 to 5.5) | 5.6 (5.4 to 5.7) | 2.1 (2.0 to 2.2) | 6.3 (5.9 to 6.7) |
| Specificity | 99.9 (99.9 to 99.9) | 99.9 (99.9 to 99.9) | 99.9 (99.9 to 99.9) | 100 (100 to 100) | 100 (100 to 100) | |
| PPV | 77.4 (76.3 to 78.5) | 79.8 (78.7 to 80.9) | 80.5 (79.4 to 81.6) | 83.0 (81.4 to 84.6) | 82.2 (80.7 to 84.8) | |
| NPV | 96.3 (96.3 to 96.3) | 93.8 (93.8 to 93.9) | 93.0 (93.0 to 93.1) | 96.2 (96.2 to 96.2) | 97.9 (97.9 to 98.0) | |
| Na<125 | Sensitivity | 13.1 (12.7 to 13.6) | 13.1 (12.7 to 13.6) | 13.6 (13.1 to 14.0) | 5.4 (5.1 to 5.7) | 15.6 (14.6 to 16.6) |
| Specificity | 99.9 (99.9 to 99.9) | 99.8 (99.8 to 99.8) | 99.8 (99.8 to 99.8) | 100 (100 to 100) | 99.9 (99.9 to 99.9) | |
| PPV | 55.7 (54.5 to 57.0) | 57.5 (56.2 to 58.8) | 57.9 (56.5 to 59.2) | 62.5 (60.4 to 64.5) | 62.3 (59.6 to 64.8) | |
| NPV | 99.0 (99.0 to 99.0) | 98.3 (98.3 to 98.4) | 98.1 (98.1 to 98.1) | 98.9 (98.9 to 98.9) | 99.4 (99.4 to 99.4) | |
| Na<120 | Sensitivity | 24.9 (24.0 to 25.9) | 24.9 (24.0 to 25.8) | 25.4 (24.5 to 26.4) | 6.3 (5.8 to 6.9) | 29.3 (27.3 to 31.3) |
| Specificity | 99.8 (99.8 to 99.8) | 99.7 (99.7 to 99.7) | 99.7 (99.7 to 99.7) | 100 (100 to 100) | 99.9 (99.9 to 99.9) | |
| PPV | 35.2 (34.0 to 36.5) | 36.3 (35.1 to 37.6) | 36.3 (35.0 to 37.6) | 50.6 (47.5 to 53.7) | 43.7 (41.0 to 46.4) | |
| NPV | 99.7 (99.7 to 99.7) | 99.5 (99.5 to 99.5) | 99.5 (99.4 to 99.5) | 99.6 (99.6 to 99.7) | 99.8 (99.8 to 99.8) | |
| Na<115 | Sensitivity | 34.3 (32.6 to 35.9) | 34.2 (32.6 to 35.9) | 34.9 (33.1 to 36.6) | 9.3 (8.3 to 10.3) | 38.8 (35.5 to 42.1) |
| Specificity | 99.8 (99.8 to 99.8) | 99.7 (99.6 to 99.7) | 99.6 (99.6 to 99.6) | 100 (100 to 100) | 99.9 (99.9 to 99.9) | |
| PPV | 18.9 (17.9 to 20.0) | 19.5 (18.5 to 20.6) | 19.5 (18.4 to 20.6) | 28.8 (26.1 to 31.7) | 24.2 (22.0 to 26.6) | |
| NPV | 99.9 (99.9 to 99.9) | 99.8 (99.8 to 99.8) | 99.8 (99.8 to 99.8) | 99.9 (99.9 to 99.9) | 99.9 (99.9 to 99.9) | |
ICD-10, International Classification of Diseases, 10th revision; NPV, negative predictive value; PPV, positive predictive value.