One kills everything including spores. The other kills nearly everything except a pile of spores. The exam needs you to know exactly which is which, and which devices get which treatment.
The short answer: Sterilization destroys all microbial life, including bacterial spores. High-level disinfection (HLD) destroys all vegetative microorganisms but cannot be relied upon to kill high numbers of bacterial spores. Critical items (sterile tissue, bloodstream) must be sterilized. Semicritical items (mucous membranes) need at least HLD. That one-spore distinction is the whole game.
Kills: all microbial life, including bacterial endospores
Methods: steam, ethylene oxide, hydrogen peroxide gas plasma, dry heat, ozone
Goes to: critical items, things entering sterile tissue or the vascular system
Proof it worked: biological indicators and cycle printouts
Kills: all vegetative microbes, except high numbers of bacterial spores
Methods: glutaraldehyde, ortho-phthalaldehyde (OPA), hydrogen peroxide liquid formulations, pasteurization
Goes to: semicritical items, things touching mucous membranes or nonintact skin
Proof it worked: chemical test strips and concentration monitoring
Bacterial endospores are the toughest microbes on the planet. They shrug off boiling, drying, and most chemicals. Sterilization methods are defined by the fact that they defeat spores; HLD methods are defined by the fact that they defeat everything except a heavy spore load. Once you lock in that sentence, half the exam questions on this topic answer themselves.
HLD sits at the top of the disinfection ladder, but the exam also tests the two rungs below it:
Notice what the bottom two rungs share with HLD: none of them are sterilization. Any item that must be sterile needs a sterilization method, never a disinfectant, no matter how "high" the level.
Our Spaulding classification guide covers this in full, but here is the decision the exam repeats in dozens of forms:
The classic trap: a question describes an endoscope and asks for the minimum acceptable reprocessing. The answer is high-level disinfection, not sterilization, because the endoscope touches mucous membranes and is therefore semicritical. The word "minimum" is the tell.
Sterilization methods live in the sterilization area: autoclaves (steam), EtO and plasma sterilizers, dry heat ovens. HLD usually lives somewhere else entirely: automated endoscope reprocessors (AERs) in the endoscopy suite or a dedicated decontamination room, where scopes are cleaned, leak-tested, soaked or cycled with an HLD chemical, rinsed, and dried. If a question asks where scopes are reprocessed, the AER and HLD chemicals are the answer, not the autoclave.
Match each item to its minimum acceptable reprocessing level. Tap an answer to check yourself.
1. A scalpel used in surgery.
Right. Anything entering sterile tissue is critical and must be sterilized. HLD is never enough for critical items.
2. A flexible endoscope used for a colonoscopy.
Right. Semicritical items need at least HLD. Sterilization is preferred where the IFU allows, but HLD is the minimum the question asked for.
3. Which process can you rely on to kill a heavy load of bacterial spores?
Right. Only sterilization promises spore kill. HLD kills most spores but not reliably at high numbers, and the lower levels do not handle spores at all.
4. Which of these is an HLD method, not a sterilization method?
Right. OPA is a liquid high-level disinfectant. Gas plasma and dry heat are sterilization methods. The word "plasma" versus "soak" is the giveaway.
Reading is good. Doing is better. Take our free CRCST practice test and see exactly where you stand across all 7 exam domains.
Take the Free Practice TestSterilization destroys all microbial life, including bacterial spores. High-level disinfection (HLD) destroys all vegetative microorganisms but does not reliably kill high numbers of bacterial endospores. HLD is the minimum acceptable level for semicritical items that contact mucous membranes, while critical items that enter sterile tissue must be sterilized.
Common liquid high-level disinfectants include glutaraldehyde, ortho-phthalaldehyde (OPA), and hydrogen peroxide-based formulations. Thermal high-level disinfection can also be achieved with pasteurization for items such as respiratory and anesthesia equipment.
High-level disinfection kills most bacterial spores but cannot be relied upon to destroy high numbers of them. That single distinction is what separates HLD from sterilization, which destroys all microbial life including spores, and it is why critical items require sterilization rather than HLD.
Flexible endoscopes are semicritical items because they contact mucous membranes, so high-level disinfection is the minimum acceptable reprocessing level. Sterilization is preferred when the device IFU allows it, and many departments now sterilize endoscopes that can tolerate a low-temperature method.
Critical items require sterilization. These are items that enter sterile tissue or the vascular system, such as surgical instruments, implants, and needles. Semicritical items require at least high-level disinfection, and noncritical items require only cleaning and low- or intermediate-level disinfection.
CRCST Exam Prep