Department of Medicine, Winthrop-University Hospital, Mineola, New York, USA.
J Nephrol. 2012 Sep-Oct;25(5):833-8. doi: 10.5301/jn.5000074.
Reset osmostat (RO) occurs in 36% of patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH) and is not often considered when evaluating hyponatremic patients. Patients with RO are not usually treated, but recent awareness that symptoms are associated with mild hyponatremia creates a therapeutic dilemma. We encountered patients with hyponatremia, hypouricemia and high urine sodium concentration (UNa), who had normal fractional excretion (FE) of urate and excreted dilute urines that were consistent with RO. We decided to test whether a normal FEurate in nonedematous hyponatremia irrespective of UNa or serum urate would identify patients with RO.
We determined FEurate in nonedematous hyponatremic patients. A diagnosis of RO was made if urine osmolality (Uosm) was <200 mOsm/kg in a random urine. We performed a modified water-loading test in patients with a normal FEurate whose random Uosm was >200 mOsm/kg.
All nonedematous hyponatremic patients with FEurate of 4%-11% had RO, as determined by Uosm <200 mOsm/kg on a random urine collection in 8 patients, or after a modified water-loading test in 6 patients. Plasma antidiuretic hormone (ADH) in 4 patients was undetectable at <1 pg/mL during water-loading. Nine patients had baseline concentrated urine, 12 had UNa >20 mmol/L, 9 were hypouricemic, yet all had a normal FEurate. Comorbidities were similar to those reported in RO.
RO, a benign form of SIADH, occurs commonly. A normal FEurate in a nonedematous hyponatremic patient is highly suggestive of RO. Determining FEurate is superior to serum urate. The therapeutic dilemma for RO must be resolved.
重置渗透压感受器（RO）在抗利尿激素分泌不当综合征（SIADH）患者中占 36%，在评估低钠血症患者时通常不会考虑到这一点。RO 患者通常不需要治疗，但最近发现症状与轻度低钠血症有关，这就产生了一个治疗上的困境。我们遇到了一些低钠血症、低尿酸血症和高尿钠浓度（UNa）的患者，他们的尿酸分数排泄（FE）正常，且排出的尿液稀释，符合 RO 的特征。我们决定测试在非水肿性低钠血症中，无论 UNa 或血清尿酸如何，正常的 FEurate 是否可以识别 RO 患者。
我们测定了非水肿性低钠血症患者的 FEurate。如果随机尿 Uosm<200 mOsm/kg，则诊断为 RO。对于 FEurate 正常且随机 Uosm>200 mOsm/kg 的患者，我们进行了改良的水负荷试验。
8 例患者的随机尿 Uosm<200 mOsm/kg，6 例患者进行了改良水负荷试验，所有 4%至 11%的 FEurate 的非水肿性低钠血症患者均被确定为 RO。4 例患者在水负荷期间，ADH 不可检测，<1 pg/mL。9 例患者有基线浓缩尿，12 例患者有 UNa>20 mmol/L，9 例患者低尿酸血症，但所有患者的 FEurate 均正常。合并症与 RO 报道的相似。
RO 是一种良性的 SIADH，很常见。非水肿性低钠血症患者的正常 FEurate 高度提示 RO。测定 FEurate 优于血清尿酸。RO 的治疗困境必须得到解决。
