Effect of environmental conditions on the performance of fentanyl field detection tests

•Trace fentanyl detection in laminar flow immunoassays and colorimetric tests.•Low resolution between positive and negative results for laminar flow immunoassays.•Elevated temperatures cause false negatives in laminar flow immunoassays.•Elevated temperatures cause false positives in colorimetric tests.•The incorporation of a blank will better inform field test results.