There sodium concentration in urine it is dosed in the laboratory to evaluate the body’s ability to conserve and eliminate this precious mineral. Sodium is in fact essential for maintaining the body’s water balance, but also for ensuring the conduction of nerve impulses and muscular and cardiac contraction.
The sodium content in urine is defined, in medical terms, sodiuria or natruria. Its values are mainly linked to renal activity and dietary intake: under normal conditions, most of the sodium introduced with food (around 90%) is eliminated in the urine. Consequently, in conditions of correct renal function and good health, Sodiuria values are proportional to dietary sodium intake. So sodium concentrations in urine collected for 24 hours can be measured for evaluate the amount of sodium introduced daily by the patient.
Understanding how much salt we are consuming is important for the doctor in order to adjust the dietary plan in the case of low-sodium diets (such as those prescribed in cases of hypertension or osteoporosis) and to understand the patient’s degree of compliance with the dietary indications already prescribed.
|Sodiuria (mmol)||Dietary sodium (mg)||Edible salt (g)|
The sodium value in urine is reported in millimoles (mmol) or milliequivalents (mEq): keep in mind that one mmol or one mEq of sodium corresponds to 23 mg of sodium. As stated, a sodium diuria of 100 mEq in the urine collected during 24 hours corresponds to a dietary intake of sodium equal to 2300 mg, which in turn is equivalent to 5.8 grams of table salt (bearing in mind that one gram of sodium chloride 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 breaks down in all those cases in which the elimination of sodium through sweating (significant physical exercise, hot-humid climates), feces (diarrhea) or urine (intake of diuretics, renal failure, some endocrine diseases) increases. .
To have more clues about the problem affecting the patient, it is very important to measure the sodium concentration, i.e. the concentration of sodium in the blood, together. For example, if you notice low sodium concentrations in the blood and high sodium levels, the patient’s kidney is likely letting out excessive amounts of sodium (due to kidney problems or the hormones that regulate their activity). If, however, the sodium concentrations in the urine and blood appear low, presumably the problem is not at the kidney level (e.g. diarrhea, persistent vomiting, sweating…).
- 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 various foods, then 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; as a result, the amount of excess electrolyte is excreted by the kidneys in the urine, so that the sodium concentration in the blood (naemia) remains within narrow limits.
- The control of sodium levels 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 that arise in these control mechanisms.
Because It Is Measured
The sodium concentration in the urine is measured to evaluate the patient’s kidney function and fluid, electrolyte and acid-base balance.
The measurement of sodium levels can be performed both as part of a regular routine medical check-up and in the monitoring of patients suffering from kidney disease. This test is also used to understand if a hypertensive subject introduces too much salt in the diet or if the imbalance derives from a significant loss of the element.
Urinary sodium testing may be ordered when blood electrolyte levels (natremia) are abnormal, as a diagnostic aid or to monitor treatment.
Urine sodium concentration can be assessed in association with:
The sodium values in urine considered normal are 50-250 mEq/24h (milliEquivalents in 24 hours).
Note: the reference interval of the test may change depending on the equipment used in the analysis laboratory. For this reason, it is preferable to consult the ranges reported directly on the report. It should also be remembered that the results of the analyzes must be evaluated as a whole by the general practitioner who knows the medical history of his patient.
High Urine Sodium – Causes
High levels of sodium in the urine (hypernatriuria) may be due to:
- Excessive sodium intake in the diet
- Excessive use of diuretics
- Acute renal failure
- Chronic kidney disease with salt loss
- Inappropriate ADH (vasopressin) secretion syndrome
- Adrenal insufficiency ( mineralocorticoid deficiency )
- Addison’s disease
- Renal tubular acidosis
- Metabolic and respiratory alkalosis
- Diabetic coma
Low Urine Sodium – Causes
The concentration of sodium in the urine may be reduced (hyponaturia) in the following cases:
- Reduced sodium intake through diet, fasting
- Congestive heart failure
- Cushing’s syndrome
- Excessive losses: vomiting, diarrhea, burns , profuse sweating, fistulas , mucoviscidosis, dehydration in general
- Physiological water retention in the premenstrual period
- Surgery ( stress syndrome )
- Reduced glomerular filtration
The test involves the collection of urine emitted during an entire day (for example: from 8 in the morning to 8 the next), in the same container and without the addition of additives.
Biological Factors Of Preanalytical Variability
The sodium concentration in urine is influenced by hydration status and nutrition , as well as the circadian rhythm . In particular, the fraction of sodium excretion during the night is equal to approximately one fifth of the daytime peak value, therefore indicating a wide variation in sodium excretion in urine throughout the day. For this reason, 24-hour urine collection is necessary.
Biological Factors Of Preanalytical 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 approximately one fifth of the daytime peak value, therefore indicating a wide variation in sodium excretion in urine throughout the day. For this reason, 24-hour urine collection is necessary.
Interpretation Of Results
If your test result is higher than normal, it may mean that your kidneys or liver are not working properly and are not using the sodium in your 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, salt-losing nephritis, tubulointerstitial pathologies, renal tubular acidosis, diuretic therapy, diabetes mellitus and syndrome of inappropriate antidiuretic hormone secretion.
High levels of sodium in the urine may physiologically depend on excessive food intake or post-menstrual diuresis.
The concentration of sodium in the urine may be lower than normal in the case of poor dietary intake, increased extra-urinary losses (due to excessive sweating or persistent diarrhea), heart failure, adrenocortical hyperfunction and nephrosis.