Electricity in Sweat Analysis: Purpose and Mechanism
The sweat electrolyte test, also known as the sweat chloride test, is a non-invasive and effective method used to diagnose Cystic Fibrosis (CF) in infants and children. This test involves stimulating sweat production and measuring the concentration of chloride ions in the sweat.
Procedure and Preparation
Before the test, the child's skin is cleaned and dried. No specific fasting or medication restrictions are usually required, but the child should be well-hydrated to produce sufficient sweat. A weak electric current drives pilocarpine, a sweat-inducing drug, into the skin through iontophoresis for about 5 minutes, causing localized sweating. Sweat is then collected on a special absorbent pad or via a device over 30 minutes. The sweat is analyzed in a laboratory to measure the chloride concentration.
During the Test
The iontophoresis process is generally painless and quick but may cause mild tingling or warmth. Sweat collection takes 30 minutes, requiring the child to stay still. The entire test can take about 1 hour.
Interpreting the Results
Elevated sweat chloride levels (>60 mEq/L) indicate CF. Values less than 30 mEq/L are normal, but intermediate values may require further testing.
When is the Test Required?
Doctors may order the sweat electrolyte test for an infant or child if they present with symptoms that could indicate CF, if the infant had a positive CF screening test, or if parents test positive as a genetic carrier.
This test is the current gold standard for CF diagnosis following newborn screening or if symptoms suggest CF. Recent advances have been made in wearable sensors for real-time sweat chloride monitoring, but these do not yet replace the clinical test.
The majority of infants over 48 hours old can undergo the test, but it is typically scheduled before the age of 4 weeks when doctors suspect an infant may have CF. The sweat electrolyte test is a crucial tool in the diagnosis and management of CF, providing valuable insights for further diagnostic steps.
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