Age-Related Increase in Plasma Urea Level and Decrease in Fractional Urea Excretion: Clinical Application in the Syndrome of Inappropriate Secretion of Antidiuretic Hormone

Wim Musch; Lies Verfaillie; Guy Decaux

doi:10.2215/CJN.00320106

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Figure 1.
Relationships between plasma urea and age (top; y = 0.229x + 18.26; r = 0.62; P < 0.001) and lack of correlation between plasma creatinine and age (bottom) in 107 patients.
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Figure 2.
Relationship between fractional urea excretion (FE urea) and age (top; y = −0.226x + 55; r = −0.41; P < 0.001) and between fractional sodium excretion (FENa) and age (bottom; y = 0.0046x + 0.365; r = 0.27; P < 0.02) in 87 patients with an urinary-to-plasma creatinine ratio between 50 and 150.

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Table 1.

Comparison of daily urea and creatinine excretion in 19 young women (<40 yr) and 15 old women (>70 yr)^a

	Young Women(n = 19)	Old Women(n = 15)
Age (yr)	31 ± 7	75 ± 6
Weight (kg)	59 ± 15	64 ± 9
Diuresis (L/24 h)	1.3 ± 0.6	1.1 ± 0.7
P Na (mEq/L)	140 ± 2	141 ± 3
P urea (mg/dl)	25 ± 7	36 ± 7^b
P creat (mg/dl)	0.8 ± 0.1	0.9 ± 0.1
P UA (mg/dl)	3.9 ± 1.5	4.2 ± 1
U osm (mOsm/kg)	684 ± 238	414 ± 119^b
FENa (%)	0.7 ± 0.3	1.1 ± 0.5^c
FE urea (%)	52 ± 15	42 ± 10^d
V/CrCl (%)	0.9 ± 0.5	1.8 ± 0.7^b
CrCl (ml/min)	107 ± 26	61 ± 16^b
Urea clearance (ml/min)	57 ± 25	25 ± 8^b
Cr excretion (mg/kg 24 h)	18.9 ± 2.3	10.9 ± 1.5^b
Urea excretion (mg/kg 24 h)	270 ± 61	196 ± 50^c
Osmole excretion (mOsm/kg 24 h)	13.9 ± 5.2	6.5 ± 3.9^b

↵^a Data are means ± SD. CrCl, creatinine clearance; creat, creatinine; FE, fractional excretion; P, plasma.
↵^b P < 0.001 versus young women.
↵^c P < 0.01 versus young women.
↵^d P < 0.05 versus young women.

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Table 2.

Comparison of usual biochemical parameters of 14 young patients with SIADH, 28 young control subjects, 18 old patients with SIADH, and 36 old control subjects^a

	Young Patients with SIADH(n = 14; 5 W/9 M)	Young Control Subject(n = 28; 10 W/18 M)	Old Patients with SIADH(n = 18; 10 W/8 M)	Old Control Subjects(n = 36; 20 W/16 M)
Age (yr)	45 ± 9	43 ± 6	75 ± 5	77 ± 8
P Na (mEq/L)	126 ± 3	140 ± 2	125 ± 5	140 ± 2
P urea (mg/dl)	18 ± 8^b,^d	27 ± 7	29 ± 8	39 ± 8^c,^d
P creat (mg/dl)	0.7 ± 0.1^c	0.9 ± 0.1	0.8 ± 0.2	0.9 ± 0.2
P UA (mg/dl)	2.4 ± 0.8^c	5 ± 1.6	2.8 ± 0.9	5.4 ± 1.5^d
U osm (mOsm/kg)	498 ± 162	515 ± 212	530 ± 153	582 ± 159
FE Na (%)	0.8 ± 0.4	0.6 ± 0.2	0.7 ± 0.3	0.7 ± 0.3
FE urea (%)	58 ± 14^b,^e	46 ± 10	44 ± 15	36 ± 9^c,^e
FE UA (%)	16 ± 6^c	8 ± 4	14 ± 6	9 ± 4^f
V/CrCl × 100 (%)	1 ± 0.3	1.1 ± 0.4	1 ± 0.4	1.1 ± 0.4

↵^a Data are means ± SD. SIADH, syndrome of inappropriate secretion of antidiuretic hormone.
↵^b P < 0.01,
↵^c P < 0.001 versus young control subjects.
↵^d P < 0.001,
↵^e P < 0.02,
↵^f P < 0.01 versus old patients with SIADH.