Indicator tape vs indicator strips: what each one proves
Why CSSDs use Class 1 indicator tape outside packs and Class 4, 5 or 6 strips inside — what each proves, how to choose by process, and how to record them.
In short: indicator tape goes on the outside of a pack and only shows that the pack has been processed. Indicator strips go inside the pack and show whether the conditions that reached the inside met the indicator’s stated values. Most CSSD policies use both: tape (Class 1) on every wrapped pack and a strip (Class 4, 5 or 6) inside.
Side by side
| Indicator tape | Indicator strip | |
|---|---|---|
| ISO 11140-1 class | Class 1 — process indicator | Class 4, 5 or 6 |
| Where it goes | Outside the pack, closing the wrap | Inside the pack, at the hardest point for the sterilant to reach |
| What it shows | The pack has been through a sterilization process | Critical variables were met inside the pack |
| When it is read | Before storage and before issue | When the pack is opened at the point of use |
| Process-specific | Yes — steam, EO and plasma tapes differ | Yes — and Class 6 is specific to one cycle |
Why tape alone is not enough
Tape reacts quickly on the surface. A wrapped tray can show fully changed tape while the centre of the tray never saw adequate steam — for example, after poor air removal or an overloaded chamber. Only an indicator inside the pack shows what happened there.
Why a strip alone is not enough
A strip inside a pack cannot be seen until the pack is opened. Without tape or a printed process indicator outside, a processed pack and an unprocessed pack look the same on the shelf, which is how unprocessed items get issued by mistake.
Choosing the class of strip
- Class 4 — responds to two or more variables; widely used for routine in-pack monitoring, including plasma and EO.
- Class 5 — responds to all critical variables of steam, with performance set against a biological indicator.
- Class 6 — responds to all critical variables of one specific cycle, such as 134 °C for 3.5 minutes; choose the one that matches your validated cycle.
For a full comparison of all six classes, see chemical indicator classes explained.
Matching tape and strips to the process
| Process | Outside | Inside |
|---|---|---|
| Steam 121 °C / 134 °C | Steam indicator tape | Steam strips, Class 4, 5 or 6 |
| Ethylene oxide | EO indicator tape | EO in-pack indicator |
| H₂O₂ plasma | Plasma indicator tape | Plasma strips, Class 4 |
Reading and recording
Compare the strip against the reference colour printed on it. A strip that has not reached the reference colour is a fail: do not use the contents, quarantine the pack and report it, and check the rest of the load. Record results in the load record so each pack can be traced to its cycle.