CRCST Exam PrepThe short answer: Flexible endoscopes are heat-sensitive semicritical items, so they get high-level disinfection (HLD) instead of steam sterilization. The reprocessing sequence is: 1) pre-clean at point of use, 2) leak test before any immersion, 3) manual cleaning with brushing of every channel, 4) visual inspection, 5) high-level disinfection or sterilization per the IFU (manual soak or AER), 6) rinse with sterile water, 7) dry with alcohol flush plus forced air, and 8) store hanging vertically with detachable parts removed. Manual cleaning is never skipped, the AER never replaces it, and every step is documented.
Why endoscopes get their own rulebook
A flexible endoscope is a long, narrow, heat-sensitive bundle of lenses, fibers, and tiny channels that blood, mucus, and tissue love to hide in. Steam sterilization would destroy it, so it cannot follow the normal instrument path. Under the Spaulding classification, scopes that contact intact mucous membranes are semicritical items, which means high-level disinfection is the minimum requirement. The exam wants you to connect those two facts: heat-sensitive plus semicritical equals HLD, performed exactly per the scope manufacturer's and the chemical manufacturer's instructions for use. Our Spaulding classification guide covers the full critical, semicritical, noncritical framework.
The 8 steps, in order
The exam loves sequence questions on this topic. Learn the order, not just the steps. Cover the list below, recite it, then check yourself.
- Pre-clean at the point of use. Starts immediately after the procedure, in the procedure room. Wipe down the exterior of the insertion tube, flush and suction enzymatic detergent through all channels, then place the scope in a closed container marked as biohazardous for transport to decontamination. Dried soil is dramatically harder to remove, so this step exists to beat the clock.
- Leak test, before any immersion. Done every single time, after pre-cleaning and before the scope touches cleaning liquid. Pressurize the scope and watch for escaping bubbles. If fluid gets inside a leaking scope during cleaning, the scope is ruined. A failed leak test means the scope is pulled from service and sent for repair immediately. Never clean, disinfect, or use a leaking scope.
- Manual cleaning. Immerse the scope and clean it with an enzymatic detergent per the IFU. Brush every accessible channel with the correctly sized brush, passing the brush completely through the channel until no debris remains. Flush and irrigate all channels, then rinse. This step is never optional and never skipped, even when an AER will be used later.
- Visual inspection. Inspect the scope for cleanliness and damage before it moves on. If it is not clean, it does not advance. A scope that is not clean cannot be disinfected reliably, because residual soil shields microbes from the disinfectant.
- High-level disinfection or sterilization. Perform HLD with a liquid chemical germicide (such as glutaraldehyde, OPA, peracetic acid, or hydrogen peroxide based products) at the concentration, temperature, and contact time the chemical manufacturer specifies, or run the validated AER cycle per the scope IFU. Check the chemical's minimum effective concentration with test strips before use. Keep the scope fully immersed with all channels filled, no air pockets.
- Rinse with sterile water. After HLD, rinse the scope and flush every channel with sterile water to remove all chemical residue. Leftover disinfectant can injure the next patient's tissues, so this rinse is thorough, not symbolic.
- Dry completely. Flush the channels with 70% isopropyl alcohol, then follow with forced air, and dry the exterior. This step is an exam favorite: residual moisture allows bacteria to multiply inside the channels during storage, undoing the disinfection you just performed.
- Store correctly and document. Hang the scope vertically in a clean, well-ventilated cabinet with all valves, caps, and detachable parts removed, so air circulates and moisture drains. Never coil tightly or leave scopes in transport cases. Record the scope identifier, patient, date and time, reprocessing personnel, HLD chemical lot and test results, and AER cycle data where applicable.
HLD chemicals: what the exam tests
| Chemical family | Exam facts |
|---|---|
| Glutaraldehyde | Classic HLD agent. Requires thorough rinsing after use. Test strips verify minimum effective concentration before each use. |
| OPA (ortho-phthalaldehyde) | Faster contact times than glutaraldehyde. Stains skin and some materials gray, a favorite exam detail. |
| Peracetic acid | Potent oxidizer used in some automated systems. Corrosive at high concentrations, so systems control exposure. |
| Hydrogen peroxide based | Used in liquid and automated formats. Concentration, temperature, and contact time all come from the manufacturer's IFU, never from memory. |
The universal rule across all of them: concentration, temperature, and contact time come from the chemical manufacturer's instructions, and MEC test strips confirm the solution is still effective. Expired or diluted chemistry disinfects nothing.
The AER: what it does and does not do
An automated endoscope reprocessor standardizes the HLD step, and many models also leak test, rinse, and dry. What the AER does not do is clean. Manual cleaning with channel brushing happens before the scope ever goes into the AER, every time. The exam's favorite AER trap is a scenario where someone skips manual cleaning because the machine will handle it. That is always the wrong answer. The AER is also validated for specific scopes and chemistries, so scope compatibility and the manufacturer's IFU still govern everything.
Drying and storage: the quiet point-losers
Steps 7 and 8 look boring, which is exactly why the exam tests them. A scope that is disinfected but stored wet can grow bacteria in its channels during storage. A scope stored coiled with valves attached traps moisture and damages the insertion tube. A scope laid in a transport case is neither ventilated nor protected. The correct picture: alcohol flush, forced air, dry exterior, hang vertically in a ventilated cabinet, valves and caps detached and stored separately. If a question asks what went wrong with a scope that passed HLD but still caused an infection, look at drying and storage first.
How the exam turns endoscopes into a trap
- "Leak test after the scope is fully immersed." Wrong. Leak test comes before immersion, every time. Immersing a leaking scope destroys it.
- "Skip manual cleaning, the AER does it." Wrong. The AER disinfects a manually cleaned scope. Brushing every channel is never skipped.
- "Flush channels with saline during pre-cleaning." Wrong. Saline is corrosive to scope components. Use the enzymatic detergent per the IFU.
- "Rinse with tap water after HLD." Wrong. Final rinse uses sterile water to remove chemical residue without reintroducing microbes.
- "Store the scope coiled in its case with valves attached." Wrong. Hang vertically, ventilated cabinet, detachable parts removed.
- "HLD contact time was shortened because the department was busy." Wrong. Time, temperature, and concentration come from the manufacturer's IFU. Chemistry does not negotiate.
- "The tech used steam sterilization on the flexible scope." Wrong. Heat-sensitive scopes cannot tolerate steam. HLD is the standard method per the IFU.