What does a positive EIA (Enzyme Immunoassay) but negative LC-MS/MS (Liquid Chromatography-Mass Spectrometry/Mass Spectrometry) result for buprenorphine and norbuprenorphine indicate?

Understanding Positive EIA with Negative LC-MS/MS for Buprenorphine and Norbuprenorphine

Direct Answer

A positive buprenorphine EIA with negative LC-MS/MS for both buprenorphine and norbuprenorphine indicates a false-positive result caused by cross-reactivity with another substance, not actual buprenorphine use. 1, 2

Why This Occurs

Immunoassay Limitations

• EIA screening tests are presumptive only and have inherent limitations in specificity due to cross-reactivity with structurally similar compounds. 1
• Standard immunoassays can generate false-positives from medications or substances that share structural similarities with buprenorphine, even when the actual drug is absent. 1, 2
• LC-MS/MS is the definitive confirmatory method that can positively identify specific substances and differentiate buprenorphine from interfering compounds. 3, 1

Known Causes of False-Positive Buprenorphine Results

• Amisulpride and sulpiride (antipsychotic medications) cause false-positive buprenorphine results on CEDIA immunoassays despite having very low cross-reactivity (0.003% and 0.002% respectively), because these drugs reach high urinary concentrations relative to the low buprenorphine cutoff. 4
• Other opioids including morphine, codeine, and dihydrocodeine can cross-react with certain buprenorphine immunoassays, particularly older CEDIA assays. 2, 4
• The specific EIA platform matters significantly—newer Lin-Zhi buprenorphine EIA demonstrates superior specificity (100%) compared to CEDIA (75%), with CEDIA generating 27 false-positives in one study, most occurring in patients positive for other opioids. 2

Clinical Interpretation Algorithm

Step 1: Obtain Complete Medication History

• Document all prescription medications, over-the-counter drugs, and supplements before interpreting results. 1, 5
• Specifically ask about antipsychotic medications (amisulpride, sulpiride) and other opioids. 4
• Include this medication list on the laboratory request form. 3

Step 2: Recognize the Discordance Pattern

• When EIA is positive but LC-MS/MS is negative for both parent drug and metabolite, this definitively rules out buprenorphine use. 1, 6, 7
• LC-MS/MS has detection limits typically less than 1 ng/mL and can detect buprenorphine, norbuprenorphine, and their glucuronide conjugates with high sensitivity. 6, 7, 8
• The absence of norbuprenorphine (the primary metabolite) on LC-MS/MS further confirms no buprenorphine exposure occurred. 6, 7

Step 3: Document as False-Positive

• Never make consequential clinical decisions (such as discharging patients from care, child custody implications, or legal actions) based solely on immunoassay results without confirmation. 1, 5
• Clearly document that confirmatory testing was negative, indicating the initial screening was a false-positive. 1
• Reassure the patient and document that no buprenorphine use occurred. 1

Critical Pitfalls to Avoid

Do Not Assume EIA Results Are Definitive

• Immunoassay screening tests are susceptible to cross-reactions and must be confirmed by an independent chemical technique like LC-MS/MS when results are unexpected or will impact patient management. 1, 9
• The positive predictive value of screening tests depends heavily on the pretest probability—testing low-risk populations increases false-positive rates. 5

Do Not Dismiss or Penalize the Patient

• The CDC explicitly warns against dismissing patients from care, making punitive decisions, or assuming medication diversion based on drug test results, as this could represent patient abandonment. 9
• Urine drug testing results can be subject to misinterpretation and might be associated with practices that harm patients, including stigmatization and inappropriate termination from care. 9

Understand Platform-Specific Differences

• Different immunoassay platforms have vastly different specificities—CEDIA demonstrated only 75% specificity compared to 100% for newer EIA platforms in head-to-head comparisons. 2
• CEDIA also demonstrated interference from structurally unrelated drugs like chloroquine and hydroxychloroquine. 2

When to Suspect Actual Interference

• Review for antipsychotic medications (amisulpride, sulpiride) which are not always listed as potential sources of interference on assay data sheets. 4
• Consider other opioids the patient may be taking, as these frequently cause cross-reactivity on older buprenorphine assays. 2, 4
• Discuss unexpected results with laboratory personnel or toxicologists before making clinical decisions. 1, 5