Decaux GT: Low Creatininuria due to Hyponatremia Is Reversible in Many Patients. Nephron DOI 10.1159/000519049
Low urinary creatinine excretion (hypocreatininuria) and low serum creatinine are often observed in euvolemic hyponatremia (due to the syndrome of inappropriate anti-diuretic hormone release; SIADH). This is presumably due to sarcopenia accompanying the state of chronic SIADH. This pathophysiological state is also often accompanied by low solute excretion, which can magnify the effect of a urinary dilution defect on water retention.
In a very nice study, Decaux elaborated on the clinical and biochemical process underlying hypocreatininuria and low solute excretion accompanying acute and chronic euvolemic hyponatremia. Urinary creatinine excretion and solute excretion were measured in patients with hyponatremia early and late, before and after the correction of hyponatremia. This was compared to similar data in normal volunteers with hyponatremia induced by dDAVP administration.
Patients with chronic hyponatremia (>1 month) had marked hypocreatininuria and this reversed after prolonged correction of hyponatremia. Solute excretion followed a similar path. Normal individual with induced acute hyponatremia did not show a reduction in creatinine excretion.
These studies suggest that the changes in creatinine and solute excretion that accompany chronic euvolemic hyponatremia (SIADH) are likely the consequence of muscle loss (sarcopenia) perhaps related to a sedentary lifestyle. They are quite reversible phenomena. Acute hyponatremia has no such effect and the reduction in creatinine excretion is delayed by months after the onset of chronic hyponatremia. The administration or oral urea for treatment of chronic euvolemic hyponatremia (SIADH) confounds the interpretation of the changes in solute excretion.
This very nice study, simple in design and execution, provides a good explanation for the finding of low creatinine excretion in chronic euvolemic hyponatremia.