What a diagnostic test kit has to tell you

A document with a fixed running order

Labeling accompanying a diagnostic product, such as a package insert, has to state a listed set of information in one place, in a format and order the regulation specifies.

There are fifteen items. Two exceptions are written into the same sentence: where information is not applicable, and where a standard for a particular product class says otherwise.

Two shortened versions are allowed. Labeling for a multiple-purpose instrument used for diagnostic purposes, not committed to specific procedures or systems, may carry only five of the fifteen. Labeling for a reagent intended as a replacement in a diagnostic system may be limited to what identifies the reagent and describes its proper use in that system.

The reason the order is fixed is that it makes documents comparable. Two inserts from two makers put the same kind of statement in the same place.

The same part carries a manufacturing rule in one line. Diagnostic products are to be manufactured in accordance with the good manufacturing practice requirements that apply to devices generally, which puts them under the same quality system as any other device.

What the test is and how it works

The first six items establish the object and its mechanism.

The names come first, proprietary and established. Then the intended use or uses of the product, and the type of procedure, with qualitative or quantitative given as the examples.

The third item is a summary and explanation of the test. It asks for a short history of the methodology with pertinent references, and, in the regulation's own words, a balanced statement of the special merits and limitations of this method or product. Where the labeling refers to another procedure, citations are included and any differences and their effect on results are explained.

The fourth is the chemical, physical, physiological or biological principles of the procedure, explained concisely with the reactions and techniques involved.

The fifth covers reagents in detail. It asks for a declaration of each reactive ingredient, and for biological material, the source and a measure of its activity. It asks for a statement identifying any catalytic or nonreactive ingredients, such as buffers, preservatives and stabilizers. And it asks for reconstitution instructions, storage instructions, any purification or treatment required, and physical, biological or chemical indications of instability or deterioration.

The sixth covers instruments, from use and installation through principles of operation, performance characteristics and specifications, operating instructions, calibration procedures, operational precautions and limitations, hazards, and service and maintenance information.

The specimen, the steps, and the arithmetic

Items seven through nine are about running the test and turning it into a number.

Specimen collection and preparation has four parts. Special precautions about collection, including special preparation of the patient as it bears on the validity of the test. Additives and preservatives needed to maintain specimen integrity. Known interfering substances. And recommended storage, handling or shipping instructions for maintaining specimen stability.

The procedure item asks for a step-by-step outline from reception of the specimen to obtaining results. Six things sit inside it. A list of all materials provided. A list of all materials required but not provided, with sizes, numbers, types and quality. The amounts of reagent, the times and the temperatures involved. A statement of how stable the final reaction material is, and the window in which it has to be measured. Details of calibration, including the reference material and the highest and lowest measurable values. And the quality control procedures and materials required, with what counts as satisfactory limits of performance.

The results item asks the maker to show its working. Explain the procedure for calculating the value of the unknown, explain each component of the formula, include a step-by-step sample calculation, and express values to the appropriate number of significant figures.

Where a test does not produce a number, the requirement adapts rather than disappearing. The regulation asks for an adequate description of expected results wherever the test provides other than quantitative results.

The four items that decide what a number is worth

Items ten through thirteen are where a careful reader should start, because they bound everything above them.

Limitation of the procedure requires a statement of the limitations, and of known extrinsic factors or interfering substances affecting results. Where further testing, more specific or more sensitive, is indicated whenever certain results are obtained, the need for that additional test has to be stated.

Expected values requires the range or ranges of expected values as obtained from studies of various populations. It also requires the maker to indicate how the range was established and to identify the population it was established on.

Specific performance characteristics requires information describing accuracy, precision, specificity and sensitivity. Those figures are related to a generally accepted method, using biological specimens from normal and abnormal populations, with a statement summarizing the data behind them.

A bibliography of pertinent references keyed to the text follows. The final two items are the name and place of business of the manufacturer, packer or distributor, and the date of issuance of the last revision of the labeling, identified as such.

That last date is small and useful. It is how a reader tells a current insert from an old one sitting in a box.

The summary item also governs comparisons to other methods. Where the labeling refers to another procedure, appropriate literature citations are included, and the labeling has to explain the nature of any differences from the original and their effect on results.

The kit sold to a person rather than a laboratory

One category of diagnostic product is written for a lay purchaser, and it gets its own labeling paragraph in language appropriate for the intended users.

The category is over-the-counter test sample collection systems for drugs of abuse testing. The labeling has to give adequate instructions for specimen collection and handling, and for preparation and mailing of the specimen to the laboratory.

It has to describe an identification system ensuring specimens are not mixed up or misidentified at the laboratory, and that user anonymity is maintained.

It has to state the intended use, including what drugs are to be identified, a quantitative description of the performance characteristics for those drugs in terms understandable to lay users, and the detection period. It has to state that confirmatory testing will be conducted on all samples that initially test positive.

And it has to give adequate instructions on how to obtain results from a person who can explain their meaning. That includes the probability of false positive and false negative results, and how to contact a trained health professional for interpretation or follow-up counseling.

These are restricted devices, and the restriction reaches the laboratory. Sample testing has to be performed in a laboratory using screening tests recognized by the agency as accurate and reliable for those specimens. That laboratory has to have, and be recognized as having, adequate capability to reliably perform the screening and confirmatory tests. Its capability includes examining the biological specimens for possible adulteration.

Sources

Each document below is named as it names itself, with the date printed on that document rather than the day it was read.

1. 21 CFR 809.10 paragraph (b) — Labeling accompanying an in vitro diagnostic product, read in full for the fifteen items, their fixed format and order, the two shortened versions, and the detailed sub-requirements for reagents, instruments, specimens, procedure, results, limitations, expected values and performance characteristics — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
2. 21 CFR 809.10 paragraph (f) — Labeling for over-the-counter test sample collection systems for drugs of abuse testing, read for the seven lay-language requirements including the anonymity system, the detection period, confirmatory testing and the false positive and false negative disclosure — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
3. 21 CFR 809.40 — Restrictions on the sale, distribution, and use of OTC test sample collection systems for drugs of abuse testing, including the requirements placed on the laboratory that performs the testing — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026
4. 21 CFR 809.20 — General requirements for manufacturers and producers of in vitro diagnostic products, requiring manufacture in accordance with the good manufacturing practice requirements of part 820 — Office of the Federal Register, Electronic Code of Federal Regulations, September 2026