Testing the Tests

DanceSafe is a nonprofit harm reduction organization that provides test kits and fentanyl test strips.  We've been working with them to evaluate some of the commercially available fentanyl test strips on the market.  Here is an example of early results from this collaboration.  

1). Fentanyl test strips

We compared three types of FTS.  In the top row are WHPM's Fen10 strips, lot F122221036, exp 2/28/25.  The middle row are BTNX 20ng/ml strips, lot DOA2204278, exp 04/11/2024.  The bottom row are BTNX 20ng/ml strips lot D805010, exp 05/12/20 (these strips expired in 2020 & were sitting unopened in a box in a harm reduction organization's storeroom).

The substances we tested are methadone (used to treat opioid addiction), lidocaine, levamisole, and procaine (all common cocaine cutting agents), and diphenhydramine (a common cutting agent in injectable opioids). Each substance was a pure compound dissolved at 10 mg/ml in DI water. 

In the photo below,  two red lines should be read as a negative result, even if one of the line is a lot weaker than the other.  A single red line indicates that fentanyl is present. Since there wasn't any fentanyl in any of these solutions, the positive test results are all false positives.  

Fentanyl test strips with 10 mg/ml solutions of methadone, lidocaine, levamisole, procaine, and diphenhydramine.A green check mark indicates a clear negative result, a green check-minus shows a negative result where one line is very faint, and a red X means the result was a false positive.  

2). Xylazine test strips

We compared two types of new xylazine test strips, BTNX DXYL-S11 lot XYL 2303001-S and WHPM/Dancesafe lot F0420230055.  The results, and photos of the strips, are available in a spreadsheet here. 

To summarize, we found that both types of xylazine test strips can detect xylazine at concentrations at or above 2,000 nanograms/mL.

Diphenhydramine, which is a common cut in heroin, did not interfere, and fentanyl did not interfere. These strips should be pretty reliable for testing injectable opioids.

A lot of other drugs, including ketamine, levamisole, and lidocaine, can cause false positives.  For example, lidocaine can give a false positive at concentrations near 10 mg/mL or higher, so samples should be prepared so that any potential lidocaine present is at a significantly lower concentration.  Because some of the interferants are common cutting agents in non-opioid drugs, these test strips should generally not be used to check for xylazine in drugs other than opioids unless you have access to a backup analysis method.