Generality
The concentration of sodium in the urine is measured in the laboratory to assess the body's ability to conserve and eliminate this precious mineral. Sodium is in fact essential to maintain the body's water balance, but also to ensure the conduction of nerve impulses and muscle and heart contraction.
Understanding how much salt we are consuming is important, for the doctor, in order to adjust the food plan in case of low-sodium dietary regimens (such as those prescribed in case of hypertension or osteoporosis) and to understand the degree of compliance of the patient with the dietary indications already prescribed.
Dietary sodium (mg)
Food salt (g)
51
1200
3,0
65
1500
3,8
100
2300
5,8
120
2760
7,02
174
4000
10,0
200
4600
11,7
The sodium value in urine is reported in millimoles (mmol) or milliequivalents (mEq): it should be noted that one mmol or one mEq of sodium correspond to 23 mg of sodium. As stated above, a sodium of 100 mEq in the urine collected during 24 hours corresponds to a dietary sodium intake of 2300 mg, in turn equivalent to 5.8 grams of table salt (bearing in mind that one gram of sodium provides 0.4 grams of sodium).
As anticipated, in normal conditions, the values of natruria reflect the dietary intake of sodium, since most of the mineral is eliminated in the urine. This relationship is no longer valid in all those cases in which the elimination of sodium through sweating increases. (important exercise, hot and humid climates), stools (diarrhea) or urine (taking diuretics, kidney failure, some endocrine diseases).
To get more clues about the problem that afflicts the patient, the joint dosage of sodemia, or the concentration of sodium in the blood, is very important. For example, if low concentrations of sodium in the blood and high levels of sodiuria are noted, the patient's kidney is likely to miss out on excessive amounts of sodium (due to kidney problems or the hormones that regulate its activity). sodium concentrations in urine and blood appear low, presumably the problem is not in the kidney (eg diarrhea, persistent vomiting, sweating ...).
What's this
- Sodiuria (or natruria) is the concentration of sodium in the urine. This electrolyte participates in numerous physiological processes and regulates fundamental functions, such as, for example, the water balance of the entire organism.
- Sodium is introduced with the diet, through added table salt (sodium chloride or NaCl) but also through various foods, then it is absorbed in the final tract of the small intestine and eliminated through urine, faeces and sweating.
- The concentration of sodium must always remain constant in the body; consequently, the amount of excess electrolyte is excreted by the kidneys in the urine, so that the concentration of sodium in the blood (sodemia) remains within narrow limits.
- Sodemia is controlled by the action of certain hormones (including aldosterone and antidiuretic hormone) and by stimulating thirst. In most cases, abnormal sodium concentrations are due to problems that arise at the level of these control mechanisms.
Because it is measured
The sodium concentration in urine is measured to evaluate the kidney function and the hydro-electrolyte and acid-base balance of the patient.
The dosage of sodiuria can be performed both in the context of a regular routine medical check-up and in the monitoring of the patient suffering from kidney diseases. This test is also used to understand if a hypertensive subject introduces too much salt with the diet or if imbalance results from a major loss of the element.
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