Table 1:
Characteristics of eligible individuals with and without hyponatremia as evidenced by recorded serum sodium levels.
| Total | Not hyponatremic during hospitalization | Hyponatremic during hospitalization | ||
|---|---|---|---|---|
| Variable | Category | N = 1 813 356 | N = 1 393 886 | N = 419 470 |
| Age category | 18–49 years | 233 118 (12.9) | 207 197 (14.9) | 25 921 (6.2) |
| 50–64 years | 269 105 (14.8) | 224 005 (16.1) | 45 100 (10.8) | |
| 65–79 years | 657 411 (36.3) | 509 665 (36.6) | 147 746 (35.2) | |
| ≥80 years | 653 722 (36.1) | 453 019 (32.5) | 200 703 (47.8) | |
| Male | 953 378 (52.6) | 717 572 (51.5) | 235 806 (56.2) | |
| Minimum sodium concentration on admission day (mmol/l) | 139 [136–141] | 140 [138–142] | 134 [131–137] | |
| Minimum sodium concentration during hospitalization (mmol/l) | 138 [135–140] | 139 [137–141] | 132 [129–133] | |
| Minimum sodium concentration after admission day (mmol/l) | 138 [135–140] | 139 [137–141] | 132 [130–134] | |
| Maximum sodium concentration on admission day (mmol/l) | 139 [137–141] | 140 [138–142] | 134 [132–138] | |
| Maximum sodium concentration during hospitalization (mmol/l) | 141 [139–143] | 141 [140–143] | 139 [136–141] | |
| Maximum sodium concentration after admission day (mmol/l) | 141 [139–143] | 141 [140–143] | 139 [136–141] | |
| Number of days with sodium measurement per week | 2.0 [1.2–3.0] | 2.0 [1.2–2.9] | 2.2 [1.4–3.0] | |
| Admission-precipitating diagnosis | Infectious disease | 40 562 (2.2) | 28 302 (2.0) | 12 260 (2.9) |
| based on ICD-10 code | Malignancy | 335 296 (18.5) | 258 669 (18.6) | 76 627 (18.3) |
| Blood disorders | 15 052 (0.8) | 10 451 (0.7) | 4601 (1.1) | |
| Endocrinological | 65 466 (3.6) | 42 244 (3.0) | 23 222 (5.5) | |
| Mental disorders | 7785 (0.4) | 6790 (0.5) | 995 (0.2) | |
| Neurological | 43 666 (2.4) | 36 206 (2.6) | 7460 (1.8) | |
| Ophthalmological | 5791 (0.3) | 5481 (0.4) | 310 (0.1) | |
| Otological | 16 750 (0.9) | 15 902 (1.1) | 848 (0.2) | |
| Cardiovascular | 361 762 (19.9) | 286 766 (20.6) | 74 996 (17.9) | |
| Respiratory | 149 954 (8.3) | 96 660 (6.9) | 53 294 (12.7) | |
| Digestive | 237 913 (13.1) | 182 506 (13.1) | 55 407 (13.2) | |
| Dermatological | 18 510 (1.0) | 13 323 (1.0) | 5187 (1.2) | |
| Musculoskeletal | 90 913 (5.0) | 77 695 (5.6) | 13 218 (3.2) | |
| Genitourinary | 121 383 (6.7) | 90 617 (6.5) | 30 766 (7.3) | |
| Pregnancy | 39 033 (2.2) | 33 086 (2.4) | 5947 (1.4) | |
| Perinatal | 50 (0.0) | 41 (0.0) | 9 (0.0) | |
| Congenital | 2866 (0.2) | 2552 (0.2) | 314 (0.1) | |
| Symptoms/signs | 21 432 (1.2) | 15 391 (1.1) | 6041 (1.4) | |
| Injury/poisoning | 200 981 (11.1) | 164 344 (11.8) | 36 637 (8.7) | |
| New diseases | 36 591 (2.0) | 25 543 (1.8) | 11 048 (2.6) | |
| External causes | 4 (0.0) | 3 (0.0) | 1 (0.0) | |
| Examinations | 1596 (0.1) | 1314 (0.1) | 282 (0.1) | |
| BMI (kg/m2) | 22.2 [19.9–24.6] | 22.4 [20.1–24.8] | 21.2 [19.0–23.7] | |
| BMI category | <18.5 kg/m2 | 191 684 (10.6) | 127 515 (9.1) | 64 169 (15.3) |
| 18.5–<25 kg/m2 | 943 232 (52.0) | 736 387 (52.8) | 206 845 (49.3) | |
| ≥25 kg/m2 | 325 582 (18.0) | 274 479 (19.7) | 51 103 (12.2) | |
| Missing | 352 858 (19.5) | 255 505 (18.3) | 97 353 (23.2) | |
| Smoking history | Non-smoker | 1 150 678 (63.5) | 886 579 (63.6) | 264 099 (63.0) |
| Current/past smoker | 460 159 (25.4) | 358 062 (25.7) | 102 097 (24.3) | |
| Missing | 202 519 (11.2) | 149 245 (10.7) | 53 274 (12.7) | |
| Consciousness level | Alert | 1 548 278 (85.4) | 1 222 968 (87.7) | 325 310 (77.6) |
| Not clear | 265 078 (14.6) | 170 918 (12.3) | 94 160 (22.4) | |
| Charlson comorbidity index | 0 [0–2] | 0 [0–1] | 0 [0–2] | |
| Activities of daily living | Independent | 971 959 (53.6) | 823 292 (59.1) | 148 667 (35.4) |
| Dependent | 700 965 (38.7) | 472 774 (33.9) | 228 191 (54.4) | |
| Missing | 140 432 (7.7) | 97 820 (7.0) | 42 612 (10.2) | |
| Unscheduled admission | 1 087 416 (60.0) | 772 877 (55.4) | 314 539 (75.0) | |
| Ambulance use | 502 607 (27.7) | 348 248 (25.0) | 154 359 (36.8) | |
| In-hospital death | 112 226 (6.2) | 54 680 (3.9) | 57 546 (13.7) | |
Data are presented N (%) for categorical variables and median [1st–3rd quartile] for continuous variables.
BMI, body mass index; ICD-10, the International Classification of Diseases, Tenth Revision