1Two kinds of evidence
Sterilization cannot be verified by inspecting the product, so we monitor the process instead. Chemical indicators respond to physical conditions — temperature, time, the presence of steam or gas — and give an answer in seconds. Biological indicators contain a known population of highly resistant spores (Geobacillus stearothermophilus for steam, Bacillus atrophaeus for EO) and answer the only question that ultimately matters: did the cycle kill? They need incubation, from 24 minutes for rapid-readout systems to 24–48 hours for conventional ones.
2The six chemical indicator types
| Type | Name | What it shows | Where it is used |
|---|---|---|---|
| 1 | Process indicator | Exposure to the process | Outside every pack (tape, pouch print) |
| 2 | Specific test | Air removal / steam penetration | Bowie-Dick test packs |
| 3 | Single-variable | One critical variable | Rarely used in healthcare |
| 4 | Multi-variable | Two or more critical variables | Inside packs |
| 5 | Integrating | All critical variables, BI-correlated | Inside packs; load release |
| 6 | Emulating | All critical variables of a specific cycle | Inside packs; cycle verification |
3How they work together
- Every pack, every cycle: a Type 1 indicator outside and a Type 4, 5 or 6 indicator inside. The external indicator sorts processed from unprocessed; the internal one confirms sterilant reached the contents.
- Every day: a Bowie-Dick (Type 2) test in each pre-vacuum sterilizer.
- At least weekly, preferably daily, and with every implant load: a biological indicator in a process challenge device.
4Advantages and limitations
Chemical indicators are inexpensive, immediate and pack-specific, but they infer lethality from physical conditions. Biological indicators prove lethality directly, but their result arrives after the load has been processed and they sample only the location where they were placed. Neither replaces the other; together with physical monitoring of the sterilizer printout they form the three pillars of sterilization monitoring.
5Conclusion
Use chemical indicators for immediate, pack-by-pack confirmation and biological indicators for periodic proof of lethality. Kangde Med supplies Type 1 tapes and Type 4, 5 and 6 strips for steam, EO, plasma and formaldehyde cycles to fit this programme.
6Frequently asked questions
How often should biological indicators be run?
Most guidelines recommend at least weekly, preferably daily, for each sterilizer, and with every load containing implants.
Can a Class 5 integrator be used to release implant loads?
A Class 5 integrator can support release of non-implant loads. Implant loads should be quarantined until the biological indicator result is available, except in documented emergencies.
