Reading a test kit label: panels, substances, cutoffs and expiration

Two kits on the same shelf can look almost identical and still screen for different things, at different levels, for different users. The details that matter are almost all printed somewhere on the box or in the leaflet inside. Here's where to look and what it means.

Why labels follow a pattern

In the United States, the labeling of in vitro diagnostic products, which includes drug screening tests, is governed by an FDA regulation, 21 CFR 809.10. Among other things it requires the label to state the product's intended use, a lot or control number, storage instructions and, for reagents, an expiration date based on those storage instructions. The accompanying insert must also describe known limitations, such as interfering substances, and the test's performance characteristics. Knowing this tells you what you should expect to find.

1. Intended use: who is this test for?

Start with the intended use statement. It tells you whether a test is meant for consumers at home (often called over-the-counter or OTC) or for professionals. Look also for the words "For In Vitro Diagnostic Use", which the regulation requires. A prescription-only device carries an "Rx only" statement. FDA notes that tests meant only for employment and insurance testing should say so in their labeling.

If a kit is labeled for professional use, it was designed with trained users in mind. That's worth knowing before relying on it at home.

2. Panels: count them, then read them

"Panel" usually means one substance or substance class the device screens for. A 5-panel test screens for five; a 12-panel for twelve. The number tells you how many, not which. Two "12-panel" products can cover different lists.

Read the actual list of substances, usually given as names with abbreviations (for example THC for marijuana, COC for cocaine). FDA's home-test page lists the kinds of substances home tests may screen for, including marijuana, cocaine, opiates, methamphetamine, amphetamines, PCP, benzodiazepines, barbiturates, methadone, tricyclic antidepressants, ecstasy and oxycodone. No single kit necessarily covers all of them, and a substance not on your kit's list isn't being tested at all. If you need a kit to screen for a particular substance, fentanyl for example, confirm that it is explicitly named on the label. Never assume a higher panel count covers it.

3. Cutoffs: the level that triggers a positive

Each substance on the list should have a cutoff, usually given in nanograms per milliliter (ng/mL). The cutoff is the concentration at which the test is designed to read positive. Below it, the test is designed to read negative.

As a real example, an FDA decision summary for one home test (510(k) number K050936) lists cutoffs of 50 ng/mL for marijuana (THC) and 300 ng/mL for cocaine. Other products can use different cutoffs for the same substance. When comparing kits, compare cutoffs substance by substance, not just panel counts. Our article on presumptive positive and negative results explains what a cutoff means for interpreting a result.

4. Limitations: the section most people skip

The insert's limitations section is where the manufacturer lists known interfering substances and other factors that affect results. It's worth reading slowly. FDA notes more generally that foods, drinks and both prescription and over-the-counter medicines can affect home results, and it specifically flags that some over-the-counter medicines can produce the same result as amphetamines. If someone takes regular medication, a pharmacist can help check the list.

5. Performance claims: read the study, not the slogan

The insert should describe the test's performance characteristics and summarize the data behind them. Be wary of a bare "99% accurate" on the front of a box with nothing behind it. FDA states plainly that no drug test of this type is 100% accurate. A meaningful claim tells you what was measured, how and with what samples.

6. Regulatory status: "cleared" isn't "approved"

Home drug screening devices such as the one in decision summary K050936 reached the U.S. market through FDA's 510(k) pathway, in which a manufacturer shows the device is substantially equivalent to one already legally on the market. FDA's own wording is that it "clears" such devices. Treat a box that says "FDA approved" with care, and if a status matters to you, check it. FDA's over-the-counter test database and its 510(k) database can be searched by test or manufacturer name.

7. Lot number, storage and expiration

• Expiration date: FDA lists degraded chemicals, from improper storage or use after the expiration date, among the reasons a test can give a negative result when a drug is present. Check the date when you buy and again before you use the kit.
• Storage: the expiration date only holds if the stated storage instructions are followed. If the box says to keep it within a temperature range, a hot car or a damp bathroom cabinet may not qualify.
• Lot number: keep the box or note the lot number until the result is settled. If you think a test malfunctioned, FDA encourages voluntary reports through its MedWatch program.

8. Instructions and timing

FDA advises reading the instructions before collecting a sample, because results have to be read within a set number of minutes. The instructions tell you how long to wait, what a valid result looks like and how to read each line. Designs vary, and on some tests a line means negative.

A quick label checklist

• Intended use matches how you'll use it (home or professional).
• The substances you need are listed by name, not just counted.
• A cutoff is given for each substance.
• The limitations section is there, and you've read it.
• Any accuracy claim is explained with data.
• The expiration date gives you enough time, and you can store it as directed.
• You know whether laboratory confirmation is included or must be arranged separately.

The random scheduling and accountability service is free. Test kits and any laboratory testing are purchased separately. P in the Cup is a scheduling and accountability service whose app is launching soon. It doesn't sell or administer tests, and we currently do not earn affiliate commissions. For a broader overview of kit types, see our test kit guide.