Table 1

Sample characteristics*

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

* Values are expressed as number (percentage) unless otherwise indicated.

† Hyponatremia was defined as serum sodium < 136 mmol/L.

‡ 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.

§ 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.

|| p-Values for the comparison between the positive and negative test groups.

Shea et al. BMC Nephrology 2008 9:5   doi:10.1186/1471-2369-9-5