Urinary sodium

The urinary sodium it is a type of analysis that measures how much sodium (Na) is deleted in a certain time interval in urine. It is a useful test to understand the nature of alterations in the quantity of mineral salts and liquids in our body, as inhypernatremia (excess sodium in the blood) andhyponatremia (sodium deficiency in the blood).

Sodium is a mineral salt very important for our body. Sodium (chemical symbol Na) together with others electrolytes as the potassium (K), the chlorine (CL), the magnesium (Mg) and it bicarbonate ion (HCO3-), contributes to the most important functions of our body, including the transmission of nerve impulses, muscle contraction and the correct absorption of substances in the cells.

Sodium is eliminated at the level of the kidneys: in physiological conditions it is filtered at the glomerular level and reabsorbed mainly (for about 70%) at the level of the proximal convoluted tubule (passive resorption) and of the loop of Henle (exchange with Cl ions).

Resorption is induced in the distal convoluted tubule from aldosterone in response hypovolemia (effective reduction in the volume of body fluids) and hyponatremia on juxtaglomerular apparatus secreting a hormone called renin.
Another hormone, L'angiotensinogen (a protein a-globulin formed by 12 amino acids) by the effect of renin, is transformed into angiotensin I (formed by 10 amino acids). Angiotensin I is in turn transformed into angiotensin II (formed by 8 residual amoniacides) due to the ACE (angiotensin converting enzyme, an enzyme that converts angiotensin).

The sodium excreted should normally correspond to the amount of sodium introduced with diet or intravenous infusions.

Normal values of urinary sodium

Normal urinary sodium values are usually between 50-200 mEq in 24-hour urine (50-200 mmol / 24 h).

Increased values of urinary sodium

  • Increased urinary excretion
    • diuretic therapy
    • Addison's disease
    • hypoaldosteronism
    • chronic nephropathies with acidosis
    • diabetic coma
    • acute renal failure (polyuric phase)
  • SIAD (syndrome of inappropriate antidiuretic hormone secretion, called ADH or vasopressin)
  • Dehydration

Decreased values of urinary sodium

    • Reduced introduction
      • Increased gastrointestinal loss, vomiting, diarrhea, fistulae, malabsorption
      • external branches
      • ion exchange resins
    • Increased skin loss
    • profuse sweating
    • extensive mucoviscidosis burns
    • Thoracentesis and paracentesis
    • Hemorrhages
    • Bartter's syndrome
    • Heart failure
    • M. of Cushing
    • Aldosteronism

      Urinary sodium in the most common pathologies

      Problem Cause of the problem Urinary sodium
      Hypovolemia (effective reduction of circulating blood volume) Extrarenal sodium loss Na less than 10 mEq / l


      Acute oliguria (drastic and rapid reduction in the amount of urine produced)
      Prerenal hyperazotemia Na less than 10 mEq / l
      Acute tubular necrosis Na greater than 30 mEq / l
      Hyponatremia (reduction in blood sodium values) Severe depletion of body fluids (and therefore of blood volume) Na less than 10 mEq / l


      Adrenergic insufficiency (inadequate production of catecholamines in response to stress) Urinary sodium greater than the amount of sodium introduced in the diet
      SIAD (syndrome of inappropriate antidiuretic hormone secretion or ADH) Urinary sodium greater than that resulting from dietary intake





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