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  1. This test is done on the serum of the patient.
    1. A random sample can be taken.
  2. Heparinized plasma and whole blood without sodium heparin may be used.
  3. 24 hours urine sample may be collected without the addition of preservatives.
    1. Can store the serum or urine at 2° C to 4 °C.
  4. Other samples can be:
    1. Feces.
    2. Sweat.
    3. Gastrointestinal fluids.


  1. Avoid hemolysis (Although it does not cause much difference in serum or plasma sodium values).
  2. Lipemic serum needs to be ultracentrifuged unless sodium is measured by the direction-selective electrodes.


  1. This is the routine workup of the patient.
  2. This is done to evaluate electrolytes and acid-base balance.
  3. To evaluate water intoxication, water balance, and dehydration.


  1. Sodium is the major cation of the extracellular fluid.
  2. The average adult contains 80 grams of sodium.
    1. 35 grams is present in the extracellular fluid.
    2. On daily basis, the average person takes 3 grams of sodium in the salt form like chloride, sulfate, or other salts.
      1. Also, excrete the same amount of 3 grams per day.
      2. Dietary need of sodium = 90 to 250 meq//day.
    3. The normal daily diet contains NaCl 8 to 15 grams which are completely absorbed in the gastrointestinal tract.

  1. Sodium is a most common cation of the blood by almost 90%.
    1. 100% of sodium is filtered through the glomerulus.
    2. 70 to 80% is reabsorbed in proximal tubules (with water and chloride).
    3. 20 to 25% is reabsorbed in the loop of Henle (with water and chloride).
    4. Kidneys are the main regulator of the sodium in the body which excretes the excess.

  1. The sodium level is the reverse of Potassium that sodium is 140 meq/L extracellular and 5 meq/L intracellular.

  1. Sodium is a major component of the extracellular osmolality. it is almost half the osmolality of the plasma.
    1. So Sodium main function is to maintain osmotic pressure and acid-base balance.
  2. Sodium also helps to transmit nerve impulses.
    1. Sodium work with potassium and calcium to maintain the neuromuscular irritability for the conduction of nerve impulses.
    2. Sodium helps in the acid-base balance through sodium bicarbonate and sodium phosphate.
    3. Sodium takes part in the cellular chemical reactions, and membrane transport. 
  3. The body can maintain the sodium level very well except few pathological conditions.
  4. Maintenance of sodium level depends upon:
    1. Renal blood flow.
    2. Carbonic anhydrase activity.
    3. Aldosterone.
    4. Other steroids hormones control through:
      1. Anterior pituitary gland.
      2. Renin enzyme secretion.
      3. Antidiuretic hormone ( ADH ).
      4. vasopressin secretion.
  5. Sodium is a result of a balance between dietary intake and renal excretion.
  6. Aldosterone acts by:
    1. stimulating the kidney to conserve the sodium.
    2. And Decrease the renal loss.
  7. ADH controls:
    1. Reabsorption of water at distal tubules.
    2. .This will effect by concentration or dilution of sodium.
  8. Physiologically Sodium and water are interlinked.
    1. Increased free body water = Sodium diluted   Na concentration decreases  Kidney conserve sodium and excrete water.
    2. Decreased free water = serum sodium will rise now kidney will conserve water.  Na level became normal.
  9. Active transport of sodium: This is found in most of the cells especially muscles and the nerves.
    1. The excitable tissue has a high concentration of Na+, K+, and ATPase.
    2. With the help of ATPase enzyme in the cell membrane, three molecules of Na+ goes out while only two molecules of K+ goes in.
    3. So inside is negatively charged.

Hyponatremia patient may have S/S :

  1. When level is <135 mmol/L ( < 125 meq/L)
    1. < 120 meq/L is severe hyponatremia.
    2. The patient will feel weakness
  2. When Level < 115 meq/L.
    1. The patient will have confusion and lethargy.
    2. May progress to stupor and coma.

Hypernatremia patient may have S/S:

  1. The patient will have dry mucous membranes.
  2. Thirst.
  3. Agitation and restless.
  4. Hyperreflexia.
  5. mania and convulsion.


  1. There is increased excretion of the sodium in the urine.
  2. It is seen in:
    1. Hypoaldosteronism.
    2. Adrenal failure.
    3. Diuretic therapy.
    4. Salt losing nephritis.
    5. Physiologically increased intake of salt.


  1. There is a decreased glomerular filtrate rate as seen in congestive heart failure.
  2. This is seen in the case of:
    1. low salt intake.
    2. There is premenstrual retention of sodium and water.
    3. Adrenocortical hyperfunction.
    4. hyperaldosteronism.


Source 1

Age meq/L
Premature cord blood 116 to 140
Premature 48 hours 128 to 148
Newborn cord blood 126 to 166
Full term 133 to 146
Infants 139 to 146
Child 138 to 145
Adult 136 to 145
>90 years 132 to 146
Urine 24 hours meq/day
  Male  Female
6 to 10 years  41 to 115  20 to 69
 10 to 14 years 63 to 177 48 to 168 
 Adult 40 to 220 
Sweat meq/L
Child and adult 10 to 40
Cystic fibrosis 70 to 190
Feces  <10          (7.8 ± 2)
Without stimulation 6.5  to 21.7
After stimulation 43 to 46
CSF 136 to 150
Amniotic fluid  
28 weeks 124 to `48
48 weeks 115 to 139

Source 2

Causes of Hypernatremia (Increased sodium) level seen in:

  1. Dehydration.
  2. insufficient water intake.
  3. Primary aldosteronism.
  4. Cushing’s syndrome.
  5. Diabetes insipidus.
  6. Coma.
  7. Excessive sodium in intravenous therapy.
  8. Excessive sweating.
  9. Vomiting.
  10. Extensive thermal burns.
  11. Loss from GI tract.

Hyponatremia (Decreased sodium) level seen in:

  1. Deficient dietary intake.
  2. decreased sodium in the I/V therapy.
  3. Diuretics.
  4. chronic renal insufficiency.
  5. Aspiration of pleural or peritoneal fluids.
  6. Excessive water intake.
  7. congestive heart failure.
  8. Ascites.
  9. Pleural effusion.
  10. Ectopic secretion of ADH.
  11. Pyloric obstruction.
  12. Malabsorption syndrome.
  13. Diabetic acidosis.
  14. Hypothyroidism.
  15. Nephrotic syndrome.
  16. Absolute loss of sodium from the body:
    1. Prolonged vomiting.
    2. Excessive sweating.
    3. Prolonged diarrhea.

Hyponatremia, when the patient is hypovolemic, may be seen in:

  1. Renal losses due to:
    1. Diuretics
    2. medullary renal disease
    3. Addison's disease
  2. External losses  due to:
    1. Gastrointestinal losses

Pseudohyponatremia may be seen in:

  1. Hyperglycemia
  2. Hyperlipidemia
  3. Hyperproteinemia

This condition is usually caused by the presence of an excess of lipids in serum. Serum sodium ions are not dissolved in the lipids.

Critical value when the patient needs an immediate intervention:

  1. Na < 120 meq/L. The patient will have weakness and neurologic symptoms.
  2. Na > 160 meq/L. This may cause heart failure.

 Note: Please see more details on Serum electrolytes

Possible References Used

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