Urinary sodium and chloride during renal salt retention.

One hundred ten episodes of renal salt retention (urinary sodium and/or chloride less than 10 mEq/L) were studied retrospectively to determine the significance of discordance of urinary sodium from chloride. In 16 episodes the urinary sodium exceeded chloride by at least 15 mEq/L. This disparity was associated with the necessity for urinary excretion of substantial quantities of poorly reabsorbed anions (penicillin, ketones, or diatrizoate), a rapidly falling serum bicarbonate level (due to resolving metabolic or developing respiratory alkalosis), or substantial renal insufficiency (serum creatinine greater than 3 mg/dL). In 14 of 110 episodes, urinary chloride exceeded urinary sodium by at least 15 mEq/L. These patients were more often oliguric and had a higher mean serum chloride than patients without this dissociation. In patients with oliguria, hyponatremia, or metabolic alkalosis, measurement of urinary sodium or chloride alone will, in a substantial number of cases, fail to detect renal salt retention. When evidence is sought for renal salt retention, both urinary sodium and chloride should be determined.