CST Diagnostics Practice Questions (20 Flashcards)

*Geobacillus stearothermophilus* is the organism of choice. It is used because it is highly resistant to moist heat but is non-pathogenic. It is a spore-forming bacterium; if the sterilization process kills these highly resistant spores, it is inferred that all other less resistant pathogens in the load have also been destroyed. **Exam Strategy:** NBSTSA frequently tests the specific names of organisms for different sterilization methods. Do not confuse this with *Bacillus atrophaeus* (used for EO and dry heat). High-yield point: *G. stearothermophilus* is also used for Hydrogen Peroxide Gas Plasma and Peracetic Acid monitoring.

A yellow color change in the **control vial** is a positive result, indicating that the spores were alive and the incubator is functioning correctly. This validates the test. If the control vial does not change color (remains purple), the test is invalid, and the results of the processed BI (the test vial) cannot be trusted. **Exam Strategy:** Don't confuse the control vial with the test vial. Test vial = should stay purple (negative/killed). Control vial = should turn yellow (positive/growth). A positive test vial means sterilization failure.

No. A Bowie-Dick test (Class 2 Chemical Indicator) only checks for **air removal** and vacuum integrity in pre-vacuum steam sterilizers to ensure no air pockets remain. It does not monitor microbial kill. A BI must still be run (daily or per load) to monitor biological lethality. **Exam Strategy:** Distinguish between Air Removal (Bowie-Dick) and Microbial Kill (BI). Note: Bowie-Dick tests are only performed on pre-vacuum cycles, never on gravity-displacement cycles. A failure indicates a leak in the vacuum system or a malfunctioning pump.

The load is rejected and considered non-sterile. Mechanical indicators (printouts, gauges, digital displays) provide the first indication of cycle failure. If the mechanical parameters for time, temperature, or pressure are not met, the load is unsterile regardless of CI results. CLINICAL REASONING: Mechanical indicators monitor the conditions inside the chamber, while CIs monitor conditions inside the packs. Both must be successful. NBSTSA FOCUS: Mechanical data is the first step in the cycle of evidence. A failure at the mechanical level supersedes any chemical indicator pass result.

Yes, the items are considered safe for use as long as the indicator reached or exceeded the pass threshold. Over-processing (exposure beyond the minimum required time/temp) does not invalidate sterility. CAUTION: While the items are sterile, the ST should visually inspect the packaging and instruments. Extreme over-exposure to heat can cause embrittlement of surgical instruments or charring/weakening of sterilization wraps, which could compromise the sterile barrier during storage. EXAM TIP: NBSTSA tests recognition of pass/fail criteria. Over-processed is a pass; Under-processed is a fail.