Sweat Electrolytes, Cystic Fibrosis and its Diagnosis
Sample
- At Least 100 mg of sweat is collected.
- Sweat is collected by applying the chemical to the skin.
- Sweat may be collected on paper after stimulation with pilocarpine and low electric current.
Precautions
- The infant should be at least 48 hours of age.
- A proper collection of sweat is very difficult.
- Take care of evaporation and contamination.
- Use gauze or filter paper which should be low in electrolytes contents.
- Wash and dry the skin of the patient thoroughly after the stimulation and before collection, with deionized water.
- Minimum sweat weight or volume is critical to get an accurate result.
Indications
- This test is done to confirm the diagnosis of cystic fibrosis.
- Sweat is tested for chloride.
Pathophysiology
- Definition: This is inherited, an autosomal recessive disease that affects nearly all the exocrine glands in the body.
- Cystic fibrosis is present at birth and persists throughout life.
- The cystic fibrosis is the quite common genetic disorders of the Caucasian population.
- Almost all exocrine glands produce an abnormal mucus that obstructs the glands and ducts and leads to tissue damage.
- Because of this abnormal exocrine secretion in cystic fibrosis develops mucous plugs that obstruct their pancreatic ducts.
- The pancreatic enzymes like amylase, lipase, trypsin, and chymotrypsin cannot be expelled into the duodenum.
- These secretions will be either absent or a very low amount in the duodenal aspirate.
- There are abnormal secretions in:
- Lung bronchi.
- Small intestine.
- Pancreatic duct.
- Bile ducts.
- Skin (sweat glands).
- There is a wide spectrum of the disease like:
- Chronic obstructive pulmonary disease.
- There is recurrent productive cough, dyspnoea, and wheezing.
- There are recurrent airway infections.
- There may be a pancreatic deficiency (pancreatic insufficiency) is due to an abnormally viscous fluid, causing decrease amylase and lipase activity.
- There is decreased trypsin and chymotrypsin level.
- There is a decreased bicarbonate level.
- pancreatic insufficiency also affects glucose metabolism through delayed insulin response.
- There may be recurrent pancreatitis.
- There may be distal intestinal obstruction syndrome.
- There is decreased fat absorption.
- There is nutritional deficiency.
- There are chronic liver diseases.
- The patient may show the effects of the disease through a reduced level of Vitamin A, carotenoids, Vitamin E, cholesterol, and essential fatty acids.
- Chronic obstructive pulmonary disease.
- In the USA 1/3 of the patients with cystic fibrosis are adults.
- These patients have an increased risk of malignancies of the GI tract, arthropathies, and osteopenia.
- There are electrolytes in the sweat.
Clinical presentation
- Cystic fibrosis is suspected in a young adult if there is a history of:
- Chronic lung disease (Bronchiectasis).
- A chronic cough with sputum production.
- Recurrent hemoptysis.
- There are sinus tenderness, purulent nasal secretion, and nasal polyps.
- Infertility.
- Pancreatitis.
- Chronic lung disease (Bronchiectasis).
- There may be abdominal pain, diarrhea, and steatorrhea.
- Almost all men have a congenital bilateral absence of the vas deferens with azoospermia.
- There may be the occurrence of the gallstones.
- There may be biliary cirrhosis.
Diagnosis:
- It depends upon:
- The clinical symptoms.
- positive sweat test of increased chloride amount.
- The serum concentration of immunoreactive trypsin is elevated in a newborn with cystic fibrosis.
- The measurement of these enzymes is the basis of the cystic fibrosis newborn screening program.
- Genetic analysis can b used for counseling of the families for gene carrier status.
Procedure for sweat collection:
- Sample collected in three stages:
- 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.
- This is the iontophoresis procedure.
- Collection of the sweat.
- Sweat can be collected on gauze or filter paper.
- Qualitative or quantitative analysis of sweat.
- 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.
- 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.
- Electrodes are stimulated and sweat is put on the gauze or paper.
- This collected sample is sent to the lab.
- There is a new method where the blood sample is not taken but sweat analyzing skin patch can be used.
- The critical issues are:
- The proper collection of sweat is very difficult.
- Avoid evaporation and contamination of the sample.
- Collect a sufficient amount and minimize skin reactions.
- 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.
- Cystic fibrosis evidence:
- Normal Sodium = <70 mmol/L (<70 meq/L)
- Cystic fibrosis = >90 mmol/L (>90 meq/L)
Sweat electrolytes increased in:
- Cystic fibrosis of the pancreas.
- Sodium
- 50 to 140 meq / L and mean maybe 103 meq / L.
- Chloride
- Normal = 4 to 60 meq / L.
- In diseases is 50 to 120 meq / L.
- Potassium
- Normal mean = 9 meq / L.
- In the disease = mean 15 meq / L.
- Cystic fibrosis transmitted autosomal recessive trait.
- Cystic fibrosis is a disorder of mucous secretion with occlusion of exocrine glands function.
- This will produce sweat with very high contents of sodium and chloride.
- Sodium
- Other causes than cystic fibrosis are:
- Addison disease (Untreated adrenal insufficiency).
- Pseudohypoaldosteronism.
- Some unusual diseases like Glucose – 6 phosphate deficiency, glycogen storage disease, and diabetes insipidus.
- Anorexia nervosa
- Atopic dermatitis.
- Familial cholestasis.
- Klinefelter syndrome.
- Nephrosis.
- Untreated hypothyroidism.
- Protein-calorie malnutrition.
- Ectodermal Dysplasia.
- Environmental deprivation.
- Nephrosis and nephrogenic diabetes inspidus.
- Psychosocial failure to thrive.