How much sweat is needed for an accurate diagnosis of cystic fibrosis (CF)?

Updated: Oct 30, 2018
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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Answer

For reliable results, collect at least 50 mg or, preferably, 100 mg of sweat, a quantity that may be difficult to obtain from young infants. This test can be inaccurate in very young infants or if an inadequate volume is collected. [34] Never pool sweat from multiple sites to obtain the required quantity because the rate of sweating determines electrolyte content.

Current macroduct collection methods allow adequate analysis with smaller volumes of sweat. If a macroduct coil is used for collection, then sweat must be stimulated with a disposable Pilogel electrode using the Webster Sweat Inducer for 5 minutes. After 30 minutes, the minimum acceptable sample is 15 µL.


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