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Table 1 Sample characteristics*

From: Sensitivity of International Classification of Diseases codes for hyponatremia among commercially insured outpatients in the United States

Characteristic Laboratory Claims Indicating Hyponatremia† p||
  All Claims (n = 40,668) Negative Test‡ (n = 39,261) Positive Test§(n = 1407)  
Age, mean (SD), y 59 (15.7) 59 (15.7) 67 (12.3) < 0.001
Female sex 24,694 (60.7) 23,769 (60.5) 925 (65.7) < 0.001
Underlying conditions and comorbidities     
   Cerebrovascular disease 1874 (4.6) 1721 (4.4) 153 (10.9) < 0.001
   Chronic obstructive pulmonary disease 4279 (10.5) 4020 (10.2) 259 (18.4) < 0.001
   Congestive heart failure 2742 (6.7) 2605 (6.6) 137 (9.7) < 0.001
   Coronary heart disease 5857 (14.4) 5560 (14.2) 297 (21.1) < 0.001
   Dementia 164 (4.0) 141 (3.5) 23 (1.6) < 0.001
   Diabetes mellitus 8342 (20.5) 8102 (20.6) 240 (17.1) 0.001
   Hypertension 14,825 (36.5) 13,997 (35.7) 828 (58.8) < 0.001
   Kidney disease 1491 (3.7) 1405 (3.6) 86 (6.1) < 0.001
   Liver cirrhosis 26 (0.1) 24 (0.1) 2 (0.1) 0.24
   Metastatic carcinoma 2325 (5.7) 2246 (5.7) 79 (5.6) 0.87
   Nephritis, nephrotic syndrome, and nephrosis 1918 (4.7) 1800 (4.6) 118 (8.4) < 0.001
   Peripheral vascular disease 1613 (4.0) 1546 (3.9) 67 (4.8) 0.12
   Rheumatic disease 1291 (3.2) 1254 (3.2) 37 (2.6) 0.24
   Syndrome of inappropriate antidiuretic hormone 157 (3.9) 91 (2.3) 66 (4.7) < 0.001
Medications known to cause hyponatremia 10,492 (25.8) 10,144 (25.8) 348 (24.7) 0.35
  1. * Values are expressed as number (percentage) unless otherwise indicated.
  2. † Hyponatremia was defined as serum sodium < 136 mmol/L.
  3. ‡ A negative test was defined as the presence of an outpatient professional claim with no ICD-9-CM code for hyponatremia or the absence of any outpatient professional claims within 15 days before or after the laboratory claim indicating hyponatremia.
  4. § A positive test was defined as the presence of an outpatient professional claim with a primary or secondary ICD-9-CM diagnosis code of hyponatremia observed within 15 days before or after the laboratory claim indicating hyponatremia.
  5. || p-Values for the comparison between the positive and negative test groups.