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      Low Sodium Excretion in SIADH Patients with Low Diuresis

      a , a , b
      Nephron Physiology
      S. Karger AG
      Siadh and salt depletion, Diuresis, Hyponatremia, Urea, Uric acid, Natriuresis

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          It is well known that during low diuresis or low effective circulating volume, salt excretion is low. The aim of this study was to find out whether salt excretion, expressed as either urinary sodium concentration (UNa) or fractional sodium excretion (FENa), and the combined use of FENa and fractional urea excretion (FEurea) still differentiate between hyponatremic SIADH and hyponatremic salt depletion (SD) patients when diuresis is low. The relationships between UNa, FENa and diuresis, indirectly estimated by the urinary to plasma creatinine ratio (U/P creat), were studied in 42 hyponatremic SIADH patients, 21 hyponatremic SD patients and 66 normonatremic controls (CO) of similar age and sex ratio. There was no significant relationship between UNa and U/P creat either in SIADH or in SD or CO patients. FENa and U/P creat were inversely correlated, both in CO (r = –0.72; p < 0.001) and in SIADH (r = –0.68; p < 0.001). SIADH and SD patients can be fairly well differentiated from one another using FENa and U/P creat. Even with high U/P creat values, SIADH patients, despite a sharp decrease in their FENa values, presented still higher FENa values than SD patients did (mean FENa = 0.3 ± 0.2% in SIADH and 0.1 ± 0.04% in SD; p < 0.05). However, FENa values of SIADH patients with low diuresis (mean FENa = 0.3 ± 0.2% for a mean U/P creat = 191 ± 40) are indistinguishable from those of SD patients with normal urine volumes (mean FENa = 0.2 ± 0.2% for a mean U/P creat = 92 ± 30). The combined use of FENa and FEurea remains a reliable way to discriminate SD patients and SIADH patients, as far as the differential limit value for FENa is narrowed to a value of 0.15%, for hyponatremic patients with U/P creat >140. Conclusion: In SIADH, FENa values are lower than 0.5%, as soon as U/P creat exceeds a value of 180. In SD patients with U/P creat values exceeding 140, FENa is lower than 0.15% and FEurea lower than 45%.

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          Clinical assessment of extracellular fluid volume in hyponatremia.

          Assessment of the status of extracellular fluid volume is important in evaluating the cause and selecting appropriate therapy for hyponatremic disorders. Since the sensitivity and specificity of clinical assessment of extracellular fluid volume status in hyponatremic states remain unknown, 58 non-edematous patients with serum sodium less than 130 meq/liter were prospectively evaluated. Patients were judged to be either normovolemic (no response of serum sodium to saline infusion) or hypovolemic (saline infusion significantly corrected hyponatremia). Hypovolemic patients had significantly higher plasma renin activity (5.0 +/- 1.5 versus 2.5 +/- 0.5 ng/ml per three hours, p less than 0.05) and norepinephrine (1,054 +/- 252 versus 519 +/- 55 pg/ml, p less than 0.05) concentrations than did normovolemic patients. Clinical assessment correctly identified only 47 percent of hypovolemic patients and 48 percent of normovolemic patients. Thus, clinical assessment was of limited sensitivity and specificity in identifying extracellular fluid volume status in these hyponatremic patients. However, the concentration of sodium in a spot urine sample clearly separated hypovolemic (mean UNa = 18.4 +/- 3.1 meq/liter) from normovolemic (mean UNa = 72 +/- 3.7 meq/liter, p less than 0.001) hyponatremic patients.

            Author and article information

            Nephron Physiol
            Nephron Physiology
            S. Karger AG
            January 2004
            02 February 2004
            : 96
            : 1
            : p11-p18
            aDepartment of Internal Medicine, Bracops Hospital, Brussels, and bResearch Unit for the Study of Hydromineral Metabolism, Erasme University Hospital, Free University of Brussels, Brussels, Belgium
            75575 Nephron Physiol 2004;96:p11–p18
            © 2004 S. Karger AG, Basel

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            : 29 October 2003
            Page count
            Figures: 3, Tables: 1, References: 11, Pages: 1
            Self URI (application/pdf): https://www.karger.com/Article/Pdf/75575
            Self URI (text/html): https://www.karger.com/Article/FullText/75575
            Self URI (journal page): https://www.karger.com/SubjectArea/Nephrology
            Original Paper

            Cardiovascular Medicine,Nephrology
            Natriuresis,Urea,Hyponatremia,Diuresis,Uric acid,Siadh and salt depletion


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