Background Interference from opiates in the Microgenics CEDIA® Buprenorphine assay is known to produce false-positive buprenorphine screening immunoassay results necessitating confirmatory buprenorphine testing by chromatography/mass spectrometry methods. Method We reviewed data on falsely positive buprenorphine immunoassay screen (cut-off ≥ 5 µg/L) but negative for buprenorphine by gas chromatography mass spectrometry (cut-off ≥ 5 µg/L) and had a positive opiate immunoassay result (cut-off ≥ 300 µg/L). The results were collected over three months, and the data were evaluated to determine whether there is an opiate immunoassay screen concentration below which a false-positive buprenorphine result will not occur. Results We found that cross-reactivity in the CEDIA® buprenorphine immunoassay by opiates at concentrations <2000 µg/L will not cause a false-positive buprenorphine result. After changing our practice to not proceed with confirmatory buprenorphine gas chromatography mass spectrometry assay when the opiate screening concentration is below an even more conservative cut-off of <1500 µg/L, we estimate a potential cost-saving of AU$ 17,810 per year without compromising clinical care. Conclusion Samples with CEDIA® opiate immunoassay result <2000 µg/L and a positive CEDIA® buprenorphine immunoassay screen do not require confirmatory testing for buprenorphine.