Specimen collection: Two FDA patches are applied to the back or upper arm for up to 7 days.
Validity checking of sweat patch should include:
(1) measurement of lactic acid concentration
(2) check for an unusual color
(3) check for a difference in color between patch A and patch B
(4) check for an unusual odor
(5) review of analytical results for evidence of an adulterant (failure to recover internal standards, unusual test reactions, damage to laboratory equipment)
(6) screening for and identification of an interfering substance or adulterant
where:
• Lactic acid is to be measured on the sweat patch, but how this information is used is not stated.
A specimen is considered adulterated if:
(1) an adulterant is identified at a level above the threshold concentration
A specimen is considered invalid if:
(1) a problem is found with the specimen
(1a) patch A has a different physical appearance than patch B
(1b) there is interference with an immunoassay for drugs on two separate aliquots
(1c) there is interference with a confirmatory test on at least two separate aliquots
(1d) there is an interfering substance that may damage laboratory equipment
(2) the interfering compound is not positively identified
