Sweat Electrolytes, Cystic Fibrosis and its Diagnosis

Sample

1. At Least 100 mg of sweat is collected.
2. Sweat is collected by applying the chemical to the skin.
3. Sweat may be collected on paper after stimulation with pilocarpine and low electric current.

Precautions

1. The infant should be at least 48 hours of age.
2. A proper collection of sweat is very difficult.
3. Take care of evaporation and contamination.
4. Use gauze or filter paper which should be low in electrolytes contents.
5. Wash and dry the skin of the patient thoroughly after the stimulation and before collection, with deionized water.
6. Minimum sweat weight or volume is critical to get an accurate result.

Indications

1. This test is done to confirm the diagnosis of cystic fibrosis.
2. Sweat is tested for chloride.

Pathophysiology

1. Definition: This is inherited, an autosomal recessive disease that affects nearly all the exocrine glands in the body.
2. Cystic fibrosis is present at birth and persists throughout life.
3. The cystic fibrosis is the quite common genetic disorders of the Caucasian population.
4. Almost all exocrine glands produce an abnormal mucus that obstructs the glands and ducts and leads to tissue damage.
5. Because of this abnormal exocrine secretion in cystic fibrosis develops mucous plugs that obstruct their pancreatic ducts.
   1. The pancreatic enzymes like amylase, lipase, trypsin, and chymotrypsin cannot be expelled into the duodenum.
   2. These secretions will be either absent or a very low amount in the duodenal aspirate.
6. There are abnormal secretions in:
   1. Lung bronchi.
   2. Small intestine.
   3. Pancreatic duct.
   4. Bile ducts.
   5. Skin (sweat glands).
7. There is a wide spectrum of the disease like:
   1. Chronic obstructive pulmonary disease.
      1. There is recurrent productive cough, dyspnoea, and wheezing.
      2. There are recurrent airway infections.
   2. There may be a pancreatic deficiency (pancreatic insufficiency) is due to an abnormally viscous fluid, causing decrease amylase and lipase activity.
      1. There is decreased trypsin and chymotrypsin level.
      2. There is a decreased bicarbonate level.
      3. pancreatic insufficiency also affects glucose metabolism through delayed insulin response.
      4.  There may be recurrent pancreatitis.
   3. There may be distal intestinal obstruction syndrome.
      1. There is decreased fat absorption.
      2. There is nutritional deficiency.
   4. There are chronic liver diseases.
   5. The patient may show the effects of the disease through a reduced level of Vitamin A, carotenoids, Vitamin E,  cholesterol, and essential fatty acids.
8. In the USA 1/3 of the patients with cystic fibrosis are adults.
9. These patients have an increased risk of malignancies of the GI tract, arthropathies, and osteopenia.
10. There are electrolytes in the sweat.

Clinical presentation

1. Cystic fibrosis is suspected in a young adult if there is a history of:
   1. Chronic lung disease (Bronchiectasis).
      1. A chronic cough with sputum production.
      2. Recurrent hemoptysis.
      3. There are sinus tenderness, purulent nasal secretion, and nasal polyps.
   2. Infertility.
   3. Pancreatitis.
2. There may be abdominal pain, diarrhea, and steatorrhea.
3. Almost all men have a congenital bilateral absence of the vas deferens with azoospermia.
4. There may be the occurrence of the gallstones.
5. There may be biliary cirrhosis.

Diagnosis:

1. It depends upon:
   1. The clinical symptoms.
   2. positive sweat test of increased chloride amount.
   3. The serum concentration of immunoreactive trypsin is elevated in a newborn with cystic fibrosis.
      1. The measurement of these enzymes is the basis of the cystic fibrosis newborn screening program.
   4. Genetic analysis can b used for counseling of the families for gene carrier status.

Procedure for sweat collection:

1. Sample collected in three stages:
   1. Stimulation for the sweating by pilocarpine (This is a muscarinic alkaloid drug that can induce sweating). There is a local injection into the skin to produce sweat and is collected.
      1. This is the iontophoresis procedure.
   2. Collection of the sweat.
      1. Sweat can be collected on gauze or filter paper.
   3. Qualitative or quantitative analysis of sweat.
2. Electrode method: Electrode is applied to the skin where sweat is produced by the colorless chemical. This may take 5 minutes to collect the sweat.
   1. Electrodes are stimulated and sweat is put on the gauze or paper.
   2. This collected sample is sent to the lab.
3. There is a new method where the blood sample is not taken but sweat analyzing skin patch can be used.
4. The critical issues are:
   1. The proper collection of sweat is very difficult.
   2. Avoid evaporation and contamination of the sample.
   3. Collect a sufficient amount and minimize skin reactions.
   4. The minimum weight or volume of the sweat is critical for the sweat test.

Normal

Source 1

Sweat Chloride (iontophoresis)

• Normal = 5 to 35 meq/L
• Marginal = 30 to 70 meq/L
• Cystic fibrosis = 60 200 meq/L

Sweat Sodium ((iontophoresis)

•  Child and adult = 10 to 40 meq/L
• Child, X: = 27 meq/L
• Adult, X: = 33  meq/L
• Cystic fibrosis = 70 to 190 meq/L
  • To convert into SI unit x 1.0 = mmol/L

Source 2

Sodium values in children

• Normal = <70 meq/L
• Abnormal = >90 meq/L
• Equivocal = 70 to 90 meq/L

Chloride values in children

• Normal = <50 meq/L
• Abnormal = >60 meq/L
• Equivocal = 50 to 60 meq/L

Another source

• Normal Chloride  = 5 to 35 mmol/L (<50 meq/L)
  • Cystic fibrosis evidence:
    • Sweat Chloride = 40 to 59 mmol/L (does not confirm the diagnosis of cystic fibrosis).
    • Sweat chloride less or equal to 39 mmol/L in an infant over 6 months of age is an unlikely diagnosis of cystic fibrosis.
    • Sweat Chloride 60 or >60 mmol/L is diagnostic of cystic fibrosis.
• Normal Sodium = <70 mmol/L (<70 meq/L)
  • Cystic fibrosis = >90 mmol/L (>90 meq/L)

Sweat electrolytes increased in:

1. Cystic fibrosis of the pancreas.
   1. Sodium
      1. 50 to 140 meq / L and mean maybe 103 meq / L.
   2. Chloride
      1. Normal = 4 to 60 meq / L.
      2. In diseases is 50 to 120 meq / L.
   3. Potassium
      1. Normal mean = 9 meq / L.
      2. In the disease = mean 15 meq / L.
   4. Cystic fibrosis transmitted autosomal recessive trait.
      1. Cystic fibrosis is a disorder of mucous secretion with occlusion of exocrine glands function.
      2. This will produce sweat with very high contents of sodium and chloride.
2. Other causes than cystic fibrosis are:
   1. Addison disease (Untreated adrenal insufficiency).
   2. Pseudohypoaldosteronism.
   3. Some unusual diseases like Glucose – 6 phosphate deficiency, glycogen storage disease, and diabetes insipidus.
   4. Anorexia nervosa
   5. Atopic dermatitis.
   6. Familial cholestasis.
   7. Klinefelter syndrome.
   8. Nephrosis.
   9. Untreated hypothyroidism.
   10. Protein-calorie malnutrition.
   11. Ectodermal Dysplasia.
   12. Environmental deprivation.
   13. Nephrosis and nephrogenic diabetes inspidus.
   14. Psychosocial failure to thrive.

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