The sweat test is diagnostic of cystic fibrosis. It is induced by intra-dermal injection of pilocarpine.
In cystic fibrosis, the chloride concentration if greater than 60 mmol/l and the sodium concentration is greater than 70 mmol/l. Sodium concentration is greater than chloride concentration in the sweat.
The mass of sweat should be greater than 100mg for an interpretable result. The test is rarely performed before three weeks of age in full term infants, as they fail to produce sweat fast enough, even in response to pilocarpine. However, if enough sweat can be produced it remains a reliable test, regardless of the age.
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