HDCN Abstract:  ASN Annual Meeting -- San Diego  

Ali NM, Imbriano L, Ilamathy E, et al.

Normal Fractional Urate Excretion (FEurate) in Reset Osmostat (RO) Eliminates RO as Subgroup of SIADH.

ASN Annual Meeting -- San Diego
J Am Soc Nephrol (Nov) 20:429A 2009

Increased FEurate accompanies hyponatremia in cerebral/renal salt wasting (RSW) and SIADH. It can differentiate RSW from SIADH when serum Na is normal, being persistently increased in RSW and normal in SIADH. We report 6 hyponatremic patients with RO, who present with normal FEurate. Their ages range from 61 to 89 years and 4 are females.

Associated conditions include: hypertension, diabetes, cardiovascular disease, colon/breast carcinoma, membranous nephropathy and gout.Initial urine osm ranged from 336 to 502 mosm/kg, urine Na 43-109 mmol/l and in one patient, 119 mosm/kg and 17 mmol/l, respectively. FEurate ranged from 3.77 to 9.38% (normal < 10%) and serum urate from 2.45 to 5.7 mg/dl, 4 being hypouricemic at < 4mg/dl. All patients diluted their urines spontaneously or after water loading to 99, 119, 116, 166, 191, and 210 mosm/kg. Five of 6 patients were treated inappropriately by fluid restriction for a presumed diagnosis of SIADH.

The diagnosis of RO was established by the excretion of dilute urines, either spontaneously or after water loading. Five of 6 patients met criteria for RSW or SIADH, but the normal FEurate places these patients in a separate pathophysiologic group from RSW and SIADH. (We report normal FEurate in psychogenic polydipsia, Kidney Int. in press) RO or type B SIADH makes up 36% of all cases of SIADH. Elimination of RO as a subgroup of SIADH has practical implications, because patients with RO should not be treated or fluid restricted.

In conclusion: FEurate should be routinely determined when evaluating patients with hyponatremia and is more informative than serum urate. A normal FEurate in a hyponatremic patient strongly suggests RO. RO requires no treatment and should be eliminated as a subgroup of SIADH.

© Copyright 2009-2010 American Society of Nephrology.Reproduced with permission.
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