Generality
The concentration of sodium in the urine is dosed in the laboratory to assess the body's ability to preserve and eliminate this precious mineral. Sodium is in fact essential for maintaining the body's water balance, but also for ensuring 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 diet plan in case of low-sodium dietary regimes (such as those prescribed in case of hypertension or osteoporosis) and to understand the degree of patient compliance with the prescribed dietary indications.
| Sodiuria (mmol) | Food 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): note that a mmol or mEq of sodium corresponds to 23 mg of sodium. According to what has been said, a 100 mEq sodiuria in urine collected during the 24 hours corresponds to a sodium dietary intake of 2300 mg, in turn equivalent to 5.8 grams of cooking salt (bearing in mind that one gram of chloride of sodium provides 0.4 grams of sodium).
As anticipated, under normal conditions, natruria values reflect the dietary intake of sodium, since most of the mineral is eliminated in the urine. This relationship is lacking in all those cases in which the elimination of sodium increases through sweating (important physical exercise, hot-humid climates), faeces (diarrhea) or urine (diuretic intake, renal failure, some endocrine diseases) .
To get more clues about the problem that afflicts the patient, the combined dosage of sodium or blood sodium 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 excessive amounts of sodium (due to kidney problems or hormones that regulate its activity). If on the other hand the sodium concentrations in the urine and blood appear low, presumably the problem is not renal (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 through the diet, through added table salt (sodium chloride or NaCl) but also through different foods, so it is absorbed in the final part of the small intestine and eliminated through urine, feces and sweating.
- The sodium concentration 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 (sodium) remains within narrow limits.
- The control of sodemia occurs through the action of some hormones (including aldosterone and antidiuretic hormone) and the stimulation of thirst. In most cases, abnormal sodium concentrations are due to problems arising at the level of these control mechanisms.
Why do you measure
The sodium concentration in the urine is measured to assess renal function and the patient's hydro-electrolyte and acid-base balance.
The dosage of sodiuria can be performed both as part of a regular routine medical check and in monitoring the patient suffering from kidney disease. This test is also used to understand if a hypertensive subject introduces too much salt with the diet or if the imbalance derives from an important loss of the element.
Related parameters
The urinary sodium test can be prescribed when the electrolyte levels in the blood (natriemia) are abnormal, as a diagnostic support or in monitoring the treatment.
The concentration of sodium in urine can be evaluated in association with:
- Chloride and potassium in serum and urine;
- Creatinine;
- Serum and urinary osmolality;
- Cortisol.
Normal values
The sodium values in urine considered normal are 50-250 mEq / 24h (milliEquivalenti in 24 hours).
Note : the examination reference interval may change depending on the instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges listed directly on the report. It should also be remembered that the results of the analyzes must be assessed as a whole by the general practitioner who knows the patient's medical history.
Sodium in High Urine - Causes
High sodium levels in urine (hypernatriuria) may be due to:
- Excessive introduction of sodium with the diet
- Excessive use of diuretics
- Acute renal failure
- Chronic nephropathies with salt loss
- Syndrome of inappropriate ADH secretion (vasopressin)
- Adrenal insufficiency (mineralocorticoid deficiency)
- Addison's disease
- Renal tubular acidosis
- Metabolic and respiratory alkalosis
- Diabetic coma
Sodium in Urine Low - Causes
The concentration of sodium in the urine may be reduced (hyponatruria) in case:
- Reduced introduction of sodium with diet, fasting
- hemorrhage
- Cirrhosis
- Congestive heart failure
- nephrosis
- Aldosteronism
- Cushing syndrome
- Excessive losses: vomiting, diarrhea, burns, profuse sweating, fistulas, mucoviscidosis, dehydration in general
- Peritonitis
- Pancreatitis
- Physiological water retention in the premenstrual period
- Surgery (stress syndrome)
- Reduced glomerular filtration
How to measure it
Sodium in urine is measured on a sample of urine collected within 24 hours.
Preparation
The examination includes the collection of urine emitted during a whole day (for example: from 8 am to 8 am on the following day), in the same container and without the addition of additives.
Biological factors of pre-analytical variability
The concentration of sodium in the urine is influenced by the state of hydration and nutrition, as well as by the circadian rhythm. In particular, the fraction of sodium excretion during the night is equal to about one fifth of the value of the diurnal peak, thus indicating a wide variation of sodium excretion with urine during the day. For this reason, 24-hour urine collection is required.
Interpretation of Results
Ipernatruria
If the test result is above the normal value, it could mean that the kidneys or liver are not functioning properly and do not use sodium in the blood as they should. This alteration must be kept under control, as it could lead to heart failure.
The causes of hypernatriuria are multiple and include: adrenal insufficiency, nephritis with loss of salts, tubulo-interstitial pathologies, renal tubular acidosis, diuretic therapy, diabetes mellitus and syndrome of inappropriate antidiuretic hormone secretion.
Elevated sodium levels in urine may physiologically depend on excessive dietary intake or post-menstrual diuresis.
Iponatruria
The concentration of sodium in the urine may be lower than the norm in the case of poor dietary intake, increased extra-urinary losses (due to excessive sweating or persistent diarrhea), heart failure, adrenocortical hyperfunction and nephrosis.
