Urine Analysis: Part 15 – Urine Sodium (Na+), Spot test, or 24 Hours Urine Sodium

November 19, 2020Lab TestsUrine Analysis

Sample

1. Can collect the random sample.
2. Collect 24 hours urine sample.
3. Urine container should be refrigerated or put on the ice.

Precautions

1. Discard the first sample and collect all other samples for 24 hours.
   1. Add the last sample to the container.
2. During collection refrigerate the samples.
3. Dietary intake of sodium salt increases the sodium level.
4. Drugs like antidiuretics increases are antibiotics, steroids, laxatives, and cough medicines.
   1. Drugs that may decrease sodium level are diuretics (furosemide, Lasix) and steroids.
   2. The increased level may be seen after caffeine, diuretics, dehydration, dopamine, and postmenstrual diuresis increased sodium intake and vomiting.
   3. The decreased sodium level is associated with corticosteroids, and propanolol, in over-hydration and stress diuresis.

Indications

1. This test evaluates fluid and electrolytes abnormalities (acid-base balance).
2. It is done to monitor the treatment.
3. Advice for diagnosing adrenal diseases.
4. Advice for the diagnosis of renal diseases.

Pathophysiology

1. Sodium is the primary regulator for retaining or excretion of the water and regulating the acid-base balance.
   1. Sodium is a major cation of the extracellular fluid.
   2. Sodium has the ability to maintain the acid-base balance by combining with the chloride and bicarbonate.
   3. it helps in the neuromuscular function.
2. Sodium is responsible for almost 50% of the osmotic strength of the plasma.
   1. It helps to maintain the osmotic pressure of the extracellular fluid.
3. The daily diet contains 8 to 15 grams (130 to 260mmol) per day.
   1. Body requirement is only 1 to 2 mmol and excess is excreted in the urine by the kidney.

Sodium Absorption and Excretion by the kidney

4. Aldosterone stimulates kidneys, decreases renal losses, and increases reabsorption.
   1. ADH control reabsorption of water at distal tubules affects Na⁺ level by dilution of urine.
   2. Na⁺ promotes normal electrolytes balance in the I/C and E/C fluids in the association of K⁺ under the influence of the Aldosterone hormone.
      1. This hormone promotes the 1:1 exchange of sodium for potassium or hydrogen ions.

Aldosterone role in Sodium metabolism

5. A natriuretic hormone produced in response to increase Na⁺ decreases reabsorption and increase Na⁺ losses.
6. Sodium transport is an active process.

Sodium and ATP role

Sodium distribution

1. In the case hyponatremia, when blood Na⁺ level is low, if it is due to inadequate intake then urine Na+ will be also low.
   1. In the case of renal dysfunction, like a chronic renal failure then urine Na⁺ will be high and serum Na⁺ will be low.
2. Maintenance of the normal urine Na+ depends upon:
   1. Dietary intake.
   2. .The kidney’s ability to excrete the Na⁺.
   3. Effect of the aldosterone produced by the adrenal glands.
      1. It causes increased reabsorption of the Na+ in distal tubules and leads to a lower level in urine Na⁺.
   4. The antidiuretic hormone which is secreted by the posterior pituitary gland.
      1. ADH controls the reabsorption of the water in the collecting ducts, causing its return to the bloodstream.
      2. It causes decreased water in the urine and an increase in the urine Na⁺.
   5. There is diurnal variation in the excretion of the Na+, this is more in the daytime than during the night.

The basis of the test:

1. This test evaluates the Na⁺ balance in the body by determining 24 hours urinary Na⁺.
2. Measurement of Na⁺ in urine gives information like :
   1. Acute renal failure.
   2. adrenal disturbances.
   3. Acid-base balance.
   4. Evaluate patients with volume depletion.
3. In acute renal failure:
   1. Raised Na⁺ level indicates Acute tubular necrosis.
   2. Low Na⁺ level  indicate prerenal azotemia.

Normal

Source 1

Conversion factor for SI unit = x 1.0 = mmol/day.

Source 2

• 24 hours urinary sodium
  • Adult = 40 to 220 meq/day (40 to 220 mmol/24 hours).
  • Child = 41 to 115 meq/24 hours (41 to 115 mmol/day).
• Random urinary sodium = > 20 meq/L.
  • Values are diet-dependent.

Another source

• 15 to 250 meq/L/day (15 to 250 mmol/L/day).
  • It depends on hydration and the intake of dietary NA⁺.

Increase urine Sodium is seen in:

1. Diuretic therapy.
2. Dehydration.
3. Adrenocortical deficiency.
4. Diabetic Ketoacidosis.
5. Chronic renal failure.
6. Excessive use of Na⁺ in the diet.
7. Hypothyroidism.
8. Toxemia of pregnancy.
9. Syndrome of inappropriate ADH secretion.

Decreased urinary sodium is seen in:

1. Congestive heart failure.
2. Diarrhea.
3. Cushing’s syndrome.
4. Malabsorption.
5. Aldosteronism (Hyperaldosteronism).
6. Inadequate sodium intake.
7. Renal diseases like kidney failure or chronic renal diseases.
8. A liver disease like cirrhosis.
9. Diaphoresis.
10. Pulmonary emphysema.
11. Inadequate intake of sodium.