In the second half of 2023, Delaware became the first U.S. state to fund a meaningful pilot of combined fentanyl-xylazine drug-checking strips at scale, distributing them through state-supported harm reduction channels. Several other states have run smaller pilots since. The combined strip is now a standing line item in some procurement conversations and a contested experiment in others. After roughly a year of field data, it is worth pulling apart what the combined format actually does and where it falls short of two single strips.
The premise of a combined strip
A combined fentanyl-xylazine strip carries two test lines on a single substrate, one tuned to fentanyl and one tuned to xylazine. A single sample, a single buffer, a single read window. The premise is that the user gets two answers for the operational cost of one test, which should reduce the per-screen consumable burden, simplify training, and increase the rate at which both analytes are actually tested when the program prioritizes one or the other.
That premise survives field testing, with caveats. The combined strip does in fact cut the consumable line items in half. It does in fact reduce the number of separate decisions a user has to make in a moment when their attention is elsewhere. The caveats are about specification, sensitivity, and the operational consequences of a strip that produces two simultaneous answers that the user has to interpret together.
What the Delaware pilot actually showed
Three findings have emerged from the Delaware-style pilots and from the academic comparison work that followed. We summarize them carefully, since the underlying study designs vary and the manufacturers tested differ.
Sensitivity is acceptable but format-dependent. Combined strips from reputable manufacturers report fentanyl and xylazine sensitivity within the operational range that single-target strips have produced. Some combined formats trade a small amount of per-target sensitivity for the integration. Whether that trade-off is acceptable depends on the program. For surveillance use it usually is. For a user making a real-time decision about whether to use a sample, the single-target strip's slightly tighter detection limit may be preferable.
Training is faster than two separate strips suggest. Field educators reported that users learned the combined-strip read pattern in a single session, with no significant confusion about which line corresponds to which analyte when the cassette is clearly labeled. The expectation that combined strips would be confusing did not hold up.
Specification language is harder than expected. Procurement officers writing RFPs for combined strips encountered two consistent problems: the lack of a standard regulatory category for combined drug-checking strips at the state level, and the absence of a clear apples-to-apples comparison framework with single-target strips on per-line sensitivity, interference, and shelf life.
The combined strip cleared the field-use bar quickly. The procurement-language bar took longer to clear, and in some states still has not.
Where the combined format helps the most
Two deployment contexts make the combined strip particularly valuable:
High-volume, low-complexity distribution. A vending machine, a mail-delivery program, or a bulk-distribution channel benefits from a single SKU that does the work of two. Inventory management is simpler, packaging is simpler, and the program's per-encounter cost drops.
Programs serving users new to drug checking. A first-time user encountering a single strip with one test line forms the mental model that drug checking produces a one-line yes/no answer. A combined strip with two simultaneous test lines forms the mental model that drug checking produces a multi-analyte answer. As the supply diversifies, the second mental model serves the user better.
Where two single strips remain preferable
Two contexts argue for keeping single-target strips:
Programs where one analyte is far more important than another. A program operating in a region where xylazine is the primary concern and fentanyl is already saturated may prefer to allocate budget to xylazine strips at the highest available sensitivity, rather than splitting the substrate.
Programs with regulatory or scope language tied to a specific analyte. Some state authorizations name "fentanyl test strips" specifically. Until the authorization language is updated to cover multi-analyte strips, the combined format may be operationally constrained even where it is functionally preferable.
What the next combined product should look like
The combined fentanyl-xylazine strip is a useful proof of concept. The next step, which the procurement market is now actively asking about, is a four-or-five-analyte combined strip (fentanyl, xylazine, medetomidine, nitazene, benzodiazepine on one substrate). The technical engineering is non-trivial. Five separate antibody pads on one membrane introduce sensitivity, cross-reactivity, and read-interpretation challenges that a two-analyte strip mostly avoids. To our knowledge, no commercial four-or-five-analyte multi-strip has been widely validated and scaled in the North American market as of early 2024.
That gap is where the next round of product development is heading. Our team is engaged in the multi-analyte strip work as part of broader portfolio development, and we expect that the engineering questions will resolve faster than the regulatory and procurement-language questions. The lessons from the Delaware pilot apply in advance: the field will adopt the combined format readily once the chemistry is solid, and the procurement language will need to catch up.
What procurement officers should ask
For a state or county RFP that includes combined strips, three questions cover most of the decision:
- What is the limit of detection per analyte on the combined strip, compared to the single-target strip from the same manufacturer.
- What is the documented cross-reactivity between the two test lines.
- What is the lot-to-lot consistency, particularly on the secondary analyte where production tolerances are most likely to drift.
The Delaware pilot's most useful lesson may be the simplest: ask the manufacturer for the comparison data, in writing, before the contract is signed. The answers separate the products that are ready for the field from the ones that are not.