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Electrolytes:- Part 2 – Sodium (Na+), Blood and Serum

November 28, 2023Chemical pathologyLab Tests

Table of Contents

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  • Sodium (Na+)
      • What sample for Sodium (Na+) is needed?
      • What precautions will you take for the estimation of Sodium (Na+)?
      • What are the Indications for Sodium (Na+)?
      • How will you describe the Pathophysiology of Sodium (Na+)?
      • What are the sources of  Sodium (Na+)?
      • What is the role of kidneys in Sodium (Na+) absorption?
      • What is the Distribution of the Sodium (Na+) in the body?
      • What are the Functions of the Sodium (Na+)?
      • How will the body maintain the sodium (Na+ ) level?
      • How will you describe the Active transport of Sodium (Na+)?
      • What are the Signs/Symptoms of Hyponatremia?
      • What are the Signs/Symptoms of Hypernatremia?
      • What is the NORMAL level of Sodium (Na+)?
      • What are the Causes of Hypernatremia (Increased serum Sodium (Na+)?
      • What are the causes of Hyponatremia (Decreased serum Sodium (Na+)?
      • How will you describe Hyponatremia (Sodium (Na+) when the patient is hypovolemic?
      • How will you define Pseudohyponatremia?
        • Define Critical value when the patient needs an immediate intervention.
      • Questions and answers:

Sodium (Na+)

What sample for Sodium (Na+) is needed?

  1. This test is done on the patient’s serum.
    1. A random sample can be taken.
  2. Heparinized plasma and whole blood without sodium heparin may be used.
  3. Twenty-four hours of urine samples 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.

What precautions will you take for the estimation of Sodium (Na+)?

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

What are the Indications for Sodium (Na+)?

  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.
  4. It is estimated to diagnose and treatment of dehydration and overhydration.

How will you describe the Pathophysiology of Sodium (Na+)?

  1. Sodium is the major cation of the extracellular fluid. It has a major influence on plasma osmolality.
    1. It is adjusted by the anti-diuretic hormone (ADH) and thirst receptors to maintain plasma volume and osmolality.
    2. Aldosterone causes tubular reabsorption of Sodium.
    3. Changes in the serum sodium reflect changes in water balance rather than sodium balance.
  2. Sodium has an important action from a quantitative standpoint because of its influence on electric neutrality.

What are the sources of  Sodium (Na+)?

  1. The average adult body contains 80 grams of Sodium.
    1. 35 grams is present in the extracellular fluid.
    2. The average person takes 3 grams of Sodium daily in salt forms 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 8 to 15 grams of NaCl, completely absorbed in the gastrointestinal tract.
Sodium (Na+) important facts

Sodium (Na+) important facts

Sodium (Na+): Sodium and Potassium distribution

Sodium (Na+): Sodium and Potassium distribution

  1. Sodium is the most common cation of the blood by almost 90%.

What is the role of kidneys in Sodium (Na+) absorption?

  1. 100% of Sodium is filtered through the glomerulus.
  2. 70% to 80% is reabsorbed in proximal tubules (water and chloride).
  3. 20% to 25% is reabsorbed in the loop of Henle (with water and chloride).
  4. Kidneys are the body’s main regulator of sodium, which excretes the excess.
Sodium (Na+): Sodium absorption and role of kidneys

Sodium (Na+): Sodium absorption and the role of kidneys

What is the Distribution of the Sodium (Na+) in the body?

  1. The sodium level is the reverse of Potassium.
  2. Sodium 140 meq/L extracellular and 5 meq/L intracellular.
  3. Because Sodium is actively pumped out of the cells, the concentration of the Na+ is a reflection of the Intracellular volume.
Sodium (Na+): Sodium distribution in intracellular and extracellular space

Sodium (Na+): Sodium distribution in intracellular and extracellular space

What are the Functions of the Sodium (Na+)?

  1. Sodium is a major component of extracellular osmolality. It is almost half the osmolality of the plasma.
    1. So, Sodium’s main function is maintaining osmotic pressure and acid-base balance.
  2. Sodium also helps to transmit nerve impulses.
    1. Sodium works with potassium and calcium to maintain 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 cellular chemical reactions and membrane transport.
  3. The body can maintain Sodium very well except for a few pathological conditions.

How will the body maintain the sodium (Na+ ) level?

  1. Maintenance of sodium level depends upon the following:
    1. Renal blood flow.
    2. Carbonic anhydrase activity.
    3. Aldosterone.
  2. Other steroid hormones can control through:
    1. Anterior pituitary gland.
    2. Renin enzyme secretion.
    3. Antidiuretic hormone ( ADH ).
    4. Vasopressin secretion.
  3. Sodium is a result of the balance between dietary intake and renal excretion.
  4. Aldosterone acts by:
    1. Stimulating the Kidney to conserve Sodium.
    2. And Decrease renal loss of Sodium.
  5. Antidiuretic harmone (ADH) controls:
    1. Reabsorption of water at distal tubules.
    2. .This will be affected by the concentration or dilution of Sodium.
  6. Physiologically, Sodium and water are interlinked.
    1. Increased free body water = Sodium diluted, Na+ concentration decreases, Kidney conserves Sodium and excretes water.
    2. Decreased free water = Serum sodium will rise, and now the Kidney will conserve water. Na+ level became normal.

How will you describe the Active transport of Sodium (Na+)?

  1. This is found in most cells, especially muscles and nerves.
  2. The excitable tissue has a high Na+, K+, and ATPase concentration.
  3. With the help of the ATPase enzyme in the cell membrane, three molecules of Na+ go out, while only two molecules of K+ go in.
  4. So, the inside is negatively charged.
Sodium (Na+): Sodium and Potassium active transport

Sodium (Na+): Sodium and Potassium active transport

Sodium (Na+): Sodium transport is active process

Sodium (Na+): Sodium transport is an active process

What are the Signs/Symptoms of Hyponatremia?

  1. When the level is <125 meq/L (<135 mmol/L).
    1. <120 meq/L is severe hyponatremia.
    2. The patient will feel weak.
  2. When Level <115 meq/L.
    1. The patient will have confusion and lethargy.
    2. May progress to a stupor and coma.
  3. There is a decreased glomerular filtrate rate, as seen in congestive heart failure.
    1. 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.

What are the Signs/Symptoms of Hypernatremia?

  1. >160 meq/L is the critical value for the patients.
    1. The patient will have dry mucous membranes.
    2. Thirst.
    3. Agitation and restlessness.
    4. Hyperreflexia.
    5. Mania and convulsion.
  2. There is increased excretion of Sodium in the urine.
  3. It is seen in the following conditions:
    1. Hypoaldosteronism.
    2. Adrenal failure.
    3. Diuretic therapy.
    4. Salt-losing nephritis.
    5. Physiologically increased intake of salt.

What is the NORMAL level of Sodium (Na+)?

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)
Saliva  meq/L
Without stimulation 6.5  to 21.7
After stimulation 43 to 46
CSF 136 to 150
Amniotic fluid meq/L
28 weeks 124 to `48
48 weeks 115 to 139
  • To convert into SI units x 1.0 = mmol/L

Source 2

  • Adult Sodium = 136 to 145 meq /L
  • Infants Sodium = 133 to 142 meq /L.
    • Premature infants = 132 to 140 meq/L.
  • Urine  Sodium      = 40 to 220 meq/day with an average sodium intake of around 8 to 15 grams/day.
    • (varies with dietary intake).
  • CSF Sodium = 136 to 150 meq/L.
  • Feces Sodium = Mean value is <10 meq/day.

What are the Causes of Hypernatremia (Increased serum Sodium (Na+)?

  1. Hypernatremia clinically may have a presentation of:
    1. Hypovolemic patients who have hypotension, tachycardia, and poor skin turgor.
    2. Euvolumic patients have normal blood pressure, normal pulse, skin turgor, and no edema.
    3. Hypervolemic patients show edema.
  2. Dehydration.
  3. Insufficient water intake.
  4. Hormones causes are:
    1. Primary aldosteronism (Adrenal insufficiency).
    2. Adrenal hyperplasia.
    3. Cushing’s syndrome.
    4. Diabetes insipidus.
    5. Steroid therapy.
  5. Coma.
  6. Excessive Sodium in intravenous therapy.
  7. Skin losses like excessive sweating and burns.
  8. Vomiting.
  9. Extensive thermal burns.
  10. Loss from GI tract.
  11. Use of diuretics.
  12. Pulmonary losses like hyperventilation.

What are the causes of Hyponatremia (Decreased serum Sodium (Na+)?

  1. Hyponatremia patients may have clinical presentations like;
    1. Hypovolemic patients will have hypotension, tachycardia, and poor skin turgor.
    2. Euvolumic patients will have normal blood pressure, normal pulse, skin turgor, and no edema.
    3. Hypervolumic patients will have edema.
  2. Deficient dietary intake.
  3. Decreased Sodium in the I/V therapy.
  4. Diuretics.
  5. Chronic renal insufficiency.
  6. Aspiration of pleural or peritoneal fluids.
  7. Excessive water intake.
  8. Congestive heart failure.
  9. Ascites.
  10. Pleural effusion.
  11. Ectopic secretion of ADH.
  12. Pyloric obstruction.
  13. Malabsorption syndrome.
  14. Diabetic acidosis.
  15. Hypothyroidism.
  16. Nephrotic syndrome.
  17. Absolute loss of Sodium from the body:
    1. Prolonged vomiting.
    2. Excessive sweating.
    3. Prolonged diarrhea.

How will you describe Hyponatremia (Sodium (Na+) when the patient is hypovolemic?

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

How will you define Pseudohyponatremia?

  1. This condition is usually caused by an excess of lipids in the serum. Serum sodium ions are not dissolved in the lipids.
    1. Hyperglycemia
    2. Hyperlipidemia
    3. Hyperproteinemia

Sodium (Na+)  level in blood and urine in various conditions:

Various clinical conditions Sodium (Na+) level in the blood  Sodium (Na+) level in urine
Diarrhea Decreased Decreased
Dehydration Increased Increased
Malabsorption Decreased Decreased
Starvation Normal Normal or Increased
Excessive sweating Decreased Decreased
Pyloric obstruction Decreased Decreased
Congestive heart failure Normal or decreased Decreased
Pulmonary emphysema Normal Decreased
Acute renal failure Decreased Decreased
Chronic renal failure Decreased Increased
Renal tubular acidosis Decreased Increased
Primary aldosteronismm Increased Decreased
Adrenal cortical insufficiency Decreased Increased
Diabetic acidosis Decreased Increased
Diabetes inspidus Normal or increased Normal
Thiazide diuretics Decreased Increased
Mercurial diuretics Decreased Increased
Diamox (Acetazolamide) Decreased Increased

Define Critical value when the patient needs an immediate intervention.

  1. Na+ <120 meq/L. The patient will have weaknesses and neurologic symptoms.
  2. Na+ >160 meq/L. This may cause heart failure.
  • Too rapid a correction of hyponatremia can lead to central pontine myelin-lysis.
  • The too-slow correction will lead to cerebral edema.

Questions and answers:

Question 1: What are the critical values of serum Sodium?
Show answer
The critical values are 1. <120 meq/L 2. >160 meq/L.
Question 2: What is the explanation of the pseudohyponatremia?
Show answer
Pseudohyponatremia is defined as the excess of lipids in the blood.

Note: Please see more details on Serum electrolytes.


Possible References Used
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