Negative control (CONTROL −)
The standard’s wording, as the sources below reproduce it:
“Indicates a control material that is intended to verify the results in the expected negative range.”
ISO 15223-1:2021, 5.5.3 · ISO 7000-2495
What it means for you
This control is made to come out negative. Run it exactly as you would run a sample and the result must be negative — on a lateral-flow test, only the control line (C) appears and no test line (T). If it reads positive, something is wrong with the kit, the way it was stored, or the way the test was run (carry-over or contamination from a positive sample is a common cause), and results from that kit or run should not be trusted until the cause is found. Professional kits often pair it with a positive control so that both kinds of error are checked; most home tests contain neither.
Whether a device is right for you is a question for your pharmacist, nurse or doctor.
- What it looks like
- A rectangle split in two: the word CONTROL on the left and a minus sign in a small cell on the right.
- Where you see it
- Professional rapid-test kits (strep A, flu, RSV, COVID-19), laboratory immunoassay and molecular test kits, and the separate external-control kits sold for them: on the vial or swab label and in the kit’s contents list.
- Other names
- CONTROL minus; CONTROL -; negative control; neg control; ISO 7000-2495
What it does not tell you
It does not say what the control is made of or how to handle and discard it — the kit insert does — and it does not set how often controls must be run; the instructions and the laboratory’s own rules decide that.
Often confused with
Indicates a control material that is intended to verify the results in the expected positive range.
More symbols in “Letters”
Batch code (LOT)ISO 15223-1:2021, 5.1.5
Catalogue number (REF)ISO 15223-1:2021, 5.1.6
Serial number (SN)ISO 15223-1:2021, 5.1.7
Authorised representative (EC REP)ISO 15223-1:2021, 5.1.2
Model number (# in a box)ISO 15223-1:2021, 5.1.10
In vitro diagnostic medical device (IVD)ISO 15223-1:2021, 5.5.1
Control (CONTROL box)ISO 15223-1:2021, 5.5.2
Medical device (MD)ISO 15223-1:2021, 5.7.7
Unique Device Identifier (UDI)ISO 15223-1:2021, 5.7.10
Rx only (prescription device)21 CFR 801.109(b)(1)
Patient number (person with #)ISO 15223-1:2021, 5.7.1Sources
ISO 15223-1 is a paid standard, so the wording above is quoted as 3 publishers’ public documents reproduce it. Each was fetched and read on the date shown:
- NE Scientific: Master Symbol Glossary (CTF-100011 Rev 01) — Shows the CONTROL box with a minus for ISO 15223-1:2021 reference no. 5.5.3 (ISO 7000-2495): “Negative control — Indicates a control material that is intended to verify the results in the expected negative range”. Checked 2026-10-16.
- Hologic: Symbols Glossary (AW-16348 Rev. 003) — Row “Negative Control — Indicates a control material that is intended to verify the results in the expected negative range.”, ISO 15223-1:2021(E) Chapter 5.5.3, ISO 7000-2495. Checked 2026-10-16.
- QuidelOrtho: QuidelOrtho Symbol Glossary — Shows the CONTROL box with a minus cell: “Negative control — Indicates a control material that is intended to verify the results in the expected negative range”, ISO 15223-1:2016 reference no. 5.5.3, ISO 7000:2014 reference no. 2495. Checked 2026-10-16.
Plain-language parts are in our own words; quotations are the sources’ wording.