Chloride (Blood Chloride, Cl¯ ) and Cystic Fibrosis

Sample

1. It is done on the serum or plasma of the patient.
2. Except emergency collect fasting sample because there is a slight decrease after the meal.
3. Chloride is estimated in sweat to rule out cystic fibrosis.
4. Other samples are CSF and 24 hours of urine.

Purpose of the test (Indications)

1. As a part of electrolytes, acid-base balance.
   1. It gives status for hydration.
2. For the diagnosis of cystic fibrosis.

Precautions

1. Separate serum or plasma from the cells, as a change in pH, will alter the distribution of Chloride.
2. Avoid hemolysis.
3. Serum, plasma, and urine are stable for one week at 1 to 4 °C or room temperature.
4. A frozen sample can be kept for one year.
5. Drugs that may increase the chloride level are ammonium chloride, acetazolamide, cortisones, androgens, and estrogens.
6. Drugs that may decrease the chloride level are aldosterone, corticosteroids, thiazide diuretics, and loop diuretics.

Pathophysiology

1. Chloride is the most abundant extracellular anion.
2. Chloride is the major negative electrolyte(anion) in the extracellular fluid.
   1. Chloride with sodium represents the majority of the osmotically active constituents of plasma. Thus the serum chlorides level changes in the same direction as sodium level, except few conditions. If the serum sodium is low, then serum chloride will also be low.
   2. The interstitial plasma fluid of chloride anion is 103 mmol/L.
   3. Its concentration in intracellular fluid (RBC) is 45 to 54 mmol/L.
   4. While the intracellular fluid of other tissue is only 1 mmol/L.
   5. Most physicians advise “electrolytes panel or profile,” which includes:
      1. Sodium.
      2. Potassium.
      3. Chloride.
      4. Bicarbonate.
         

         Electrolytes	Extracellular fluid (ECF) meq/L	Intracellular fluid (ICF)  meq/L
         Sodium	142	10
         Potassium	5	156
         Chloride	104	4
         Bicarbonate	24	12

3. Chloride ions in the food are absorbed entirely in the intestine.
   1. They are filtered from the plasma at the glomerular level and passively reabsorbed, along with Na⁺ in the proximal tubules.
4. Chloride interacts with sodium to maintain the osmotic pressure of blood.
5. Its main purpose is to maintain the electrical neutrality of salt with sodium.
6. Aldosterone increases the reabsorption of sodium, than Chloride maintains neutrality.
7. Chloride acts as a buffer to help in acid-base balance.
   1. The concentration of the Cl^– changes inversely with the changes in concentration of HCO₃^–.
      

      Chloride functions

7. Chloride filtered at glomerulus passively and reabsorbed at proximal tubules. Further absorption at the loop of Henle.
   1. There is a chloride pump in the ascending limb of the loop of Henle.
   2. Sodium is absorbed passively, while Chloride is absorbed actively by the pump.
   3. Excess Chloride is excreted in the urine and sweat.
      

      Chloride excretion and absorption

8. Functions :
   1. Maintenance of water balance and osmotic pressure with the help of sodium.
   2. Chloride moves into cells in exchange for bicarbonate produced in the cells.
   3. It can maintain electrical neutrality.
   4. It helps as a buffer to help in the acid-base balance.
   5. Anion-cation balance in the extracellular fluid compartment.
   6. Chloride provides electroneutrality, particularly with Na⁺.
      

      Chloride maintains electrolyte balance.

Sweat test for cystic fibrosis:

The level of sodium and chloride is higher in patients with cystic fibrosis.

For a definite diagnosis, sweat is collected. The sample should weigh >50 mg and weighing <50 mg is not adequate.

In children sweat sodium >70 meq/L and chloride >60 meq/L are abnormal and are diagnostic of cystic fibrosis.

Sign and symptoms of Hypochloremia

1. There is the loss of Cl^–, usually resulting from hyponatremia or elevated HCO3^– concentration, as in metabolic alkalosis.
   1. This will develop with vomiting and loss of HCL.
   2. Hypochloremia characterizes cystic fibrosis.
   3. Restricted use of salt or in use of diuretics is accompanied by Cl^– deficiency.
2. There is hyperstimulation of the nervous system and muscles.
3. Shallow breathing.
4. Hypotension.
5. Tetany.

Sign and symptoms of Hyperchloremia

1. This will take place when there is too much sodium or too little bicarbonate.
   1. More than a normal amount of Cl^/ can be expected with hypernatremia or metabolic acidosis.
   2. Ingestion of excessive Cl- accompanies the use of an ammonium chloride diuretic.
2. Usually, no specific symptoms are associated with chloride excess.
   1. There are lethargy and weakness.
   2. Deep breathing.

Normal

Source 1

1. Serum = 95 to 105 meq / L (98 to 106 mmol/L)
2. Urine = 110 to 250 meq/ 24 hours
3. Sweat:
   1. normal = 5 to 40 meq/L
   2. marginal value =  30 to 70 meq/L
   3. cystic fibrosis = 60 to 200 meq/L
4. CSF :
   1. Infant  = 110 to 130 meq/L
   2. Adult  =  118 to 132 meq/L
      1. These are 15% higher than those in serum.
5. Saliva without stimulation  =  5 to 20 meq/L

Other Sources 

Sample	meq/L
Serum or plasma
Cord blood	96 to 104
Premature infant	95 to 110
0 to 30 days	98 to 113
Adult	98 to 107
>90 years	98 to 111
Urine 24 hours	meq/24 hours
Infants	2 to 10
<6 years	15 to 40
Male 6 to 10 years	36 to 110
Female 6 to 10 years	18 to 74
Male 10 to 14 years	64 to 176
Female 10 to 14 years	36 to 173
Adult	110 to 250
>60 years	95 to 195
Cerebrospinal fluid	meq/L
Infant	110 to 130
Adult	118 to 132
Feces  24 hours	meq/L
	3.2 to ± 0.7
Sweat	meq/L
Normal	5 to 35
Marginal	30 to 70
Cystic fibrosis	60 to 200
Saliva	meq/L
normal without stimulation	5 to 20

Increased level(Hyperchloremia):

1. urinary tract obstruction, glomerulonephritis, renal tubular acidosis, and acute renal failure.
2. Diabetes Insipidus.
3. Salicylate intoxication.
4. Prolonged diarrhea with the loss of sodium bicarbonate.
5. Respiratory alkalosis.
6. Some cases of primary hyperparathyroidism.
7. Maybe because of excessive intake.
8. Eclampsia.
9. Cushing syndrome.
10. Renal tubular acidosis.
11. Dehydration.
12. Due to the excessive infusion of normal saline.
13. Hyperventilation.

Decreased level (Hypochloremia):

1. excessive sweating.
2. Prolonged vomiting.
3. Gastric suction.
4. Salt losing nephritis.
5. Addisonian crises.
6. Metabolic acidosis, associated with increased organic anions.
7. Aldosteronism.
8. Respiratory acidosis.
9. Water intoxication.
10. Diuretic therapy.
11. Hypokalemia.
12. Burn
13. Overhydration.

Serum electrolytes in various conditions:

Clinical condition	pH	Chloride meq/L	Sodium meq/L	Potassium meq/L	Bicarbonate meq/L
Normal	7.35 to 7.45	100 to 106	136 to 145	3.5 to 5.0	24 to 26
Diabetic acidosis	7.2	80	122	5.6	10
Severe diarrhea	7.2	96	128	3.2	12
Vomiting	7.6	94	150	3.2	38
Respiratory acidosis	7.1	80	142	5.5	30
Respiratory alkalosis	7.6	112	136	5.5	14

Critical values in serum or plasma are:

• High value = >115 meq/L.
• Low value = <80 meq/L.

 

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