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<135Sensitivity1.8 (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)
Specificity100 (100 to 100)100 (100 to 100)100 (100 to 100)100 (100 to 100)100 (100 to 100)
PPV92.5 (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)
NPV86.2 (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<130Sensitivity5.3 (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)
Specificity99.9 (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)
PPV77.4 (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)
NPV96.3 (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<125Sensitivity13.1 (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)
Specificity99.9 (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)
PPV55.7 (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)
NPV99.0 (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<120Sensitivity24.9 (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)
Specificity99.8 (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)
PPV35.2 (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)
NPV99.7 (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<115Sensitivity34.3 (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)
Specificity99.8 (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)
PPV18.9 (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)
NPV99.9 (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.